Back in December of '09 we reviewed a couple of water heaters that we thought were pretty stylish. The American Council for an Energy Efficient Economy (ACEEE) has created a chart which looks at operating efficiencies and lifetime costs for nine different types of water heaters. We promoted two types of water heaters, one being the high-eff. electric storage, the other being a heat-pump water heater (HPWH). We were impressed by both. The ACEEE study shows the HPWH to be the most efficient unit as well as having the lowest lifetime operating cost. (N.B. that ACEEE lists $190 as annual operating cost while Ruud lists their unit as costing $234 per year. Comparisons made with the average of $212/yr). In fact, compared to a standard electric water heater, the HPWH has a payback period of a little over three and a half years. Even the high-eff. electric has a 3 year payback period over the standard electric tank. After that, though, the HPWH will be ten times cheaper to operate than the high-eff. over the standard electric tank. (Payback period calculated by taking difference of installed costs and dividing by the difference in yearly energy costs.)
Note that if you currently use an oil-fired boiler, you almost can't afford to NOT switch to a new water heater. Even a minimum efficiency electric heater will have a 4 year payback period. If gas is available in your area and you prefer it in case of an electric outage, payback period is about 3 years for a conventional gas heater. Even a HPWH will pay back in 4 years. (Payback period calculated by taking installed cost and dividing by the difference in yearly energy costs.)
Of note is that some state and federal tax credits will offset the cost of a high-efficiency water heater even further making your payback almost immediate. The federal 30% tax credit for energy efficient improvements brings the payback period of a HPWH to less than two years (20 months) compared to a standard electric tank heater.
Istockhouseplans doesn't always designate a space for a water heater within the house (and attached garages in our designs are rare). Therefore we are pleased to see that the HPWH is a high contender for cost and efficiency. These types of units can be put in crawlspaces, basements, and even outside in a milder climate. For colder climates a little attached shed on the side or back of the house would suffice fine. As always, check with your local codes, etc, etc.
Tuesday, January 3, 2012
Tuesday, December 20, 2011
Heat Load Calculator
A while back we posted a series on the mechanics of calculating the heat load of your home. At the end we promised to offer up an Excel file that is set up for you to do your own calculations without getting a headache or hand cramp
The calculator comes pre-filled with info from our Houston 2448. Everything in light yellow can be modified. The file or the rest of the cells are not locked. This should be considered open-source, AKA modify at your own risk. If you enter any values into white cells, you may destroy formulas. There are also no fail safes or error checking in here. Double check your work.
There are 7 components listed: slab, floor, walls above and below grade, windows, doors, and roof. Each of these has inputs for area and R-value. Note that windows should be input as U-value. When inputting wall area, don't take windows or doors into account. They are automatically deducted from the wall area in the calculations. Outside design temperature can be modified for the first four items; remaining values are derived from those.
All the work is shown on the following columns. The UA value, Δt and Btu/hr values are shown. Indoor temp can be changed to your desired setpoint. To the right is a little table with all sorts of nerdy calculations in it. Percent of load tells you which component is losing the most heat. Cost/hr tells you how much it costs. In the example you can see that more than half the heat loss in this house is through the walls. Of course! There is only R-15 in the walls! You can also see that increasing to R-21 doesn't do much for that factor. Increase the walls to R-30 and you can get that component down to about 1/3 of the heat load. Still high. Note that the rest of the load percentages change as you change the area or R-value of an item.
Lower down on the page is a place to take leakiness of the house into account. Input your target or measured ACH50 as well as volume of the home. You should only change the HC if you know what you're doing.
The final input is for number of bedrooms or potential bedrooms. This little calc will determine internal gains from humans. It takes the number of bedrooms and adds 1 person per ASHRAE standards. If there will only be two people living in your 3000sf house, enter one bedroom for kicks.
Total peak heating load is given near the bottom of the sheet. The final table gives an idea of how much of what types of heat is needed to keep the house comfortable. A forced air unit size and efficiency can be entered. As you can see, even this is WAY too big for the house. Even 2 1kW cadet heaters will do fine. In this case we would recommend a 500W heater in each of the bedrooms and bathrooms with a 1kW in the great room. Still a bit much but at least reasonable. Perhaps a mini-split heat pump would do for efficiency as well as adding some cooling if you are in the South.
This calculator should be used for entertainment purposes only. No guarantees about the results or performance of this tool are made or implied. If you break it, you bought it. If you find errors, please feel free to let us know. If somebody who knows javascript is bored, we would be thrilled to turn this into an online tool.
The calculator comes pre-filled with info from our Houston 2448. Everything in light yellow can be modified. The file or the rest of the cells are not locked. This should be considered open-source, AKA modify at your own risk. If you enter any values into white cells, you may destroy formulas. There are also no fail safes or error checking in here. Double check your work.
There are 7 components listed: slab, floor, walls above and below grade, windows, doors, and roof. Each of these has inputs for area and R-value. Note that windows should be input as U-value. When inputting wall area, don't take windows or doors into account. They are automatically deducted from the wall area in the calculations. Outside design temperature can be modified for the first four items; remaining values are derived from those.
All the work is shown on the following columns. The UA value, Δt and Btu/hr values are shown. Indoor temp can be changed to your desired setpoint. To the right is a little table with all sorts of nerdy calculations in it. Percent of load tells you which component is losing the most heat. Cost/hr tells you how much it costs. In the example you can see that more than half the heat loss in this house is through the walls. Of course! There is only R-15 in the walls! You can also see that increasing to R-21 doesn't do much for that factor. Increase the walls to R-30 and you can get that component down to about 1/3 of the heat load. Still high. Note that the rest of the load percentages change as you change the area or R-value of an item.
Lower down on the page is a place to take leakiness of the house into account. Input your target or measured ACH50 as well as volume of the home. You should only change the HC if you know what you're doing.
The final input is for number of bedrooms or potential bedrooms. This little calc will determine internal gains from humans. It takes the number of bedrooms and adds 1 person per ASHRAE standards. If there will only be two people living in your 3000sf house, enter one bedroom for kicks.
Total peak heating load is given near the bottom of the sheet. The final table gives an idea of how much of what types of heat is needed to keep the house comfortable. A forced air unit size and efficiency can be entered. As you can see, even this is WAY too big for the house. Even 2 1kW cadet heaters will do fine. In this case we would recommend a 500W heater in each of the bedrooms and bathrooms with a 1kW in the great room. Still a bit much but at least reasonable. Perhaps a mini-split heat pump would do for efficiency as well as adding some cooling if you are in the South.
This calculator should be used for entertainment purposes only. No guarantees about the results or performance of this tool are made or implied. If you break it, you bought it. If you find errors, please feel free to let us know. If somebody who knows javascript is bored, we would be thrilled to turn this into an online tool.
Tuesday, December 13, 2011
Massive Influx of Plans
In what might be described as an heroic maneuver, we at Istockhouseplans just cleared out a bunch of backlog and loaded more than a handful of plans. The final damage? Seven in one blow! Listed below is the latest additions to the lineup:
The Wilsada A 1416A joins her brother the Wilsada 1416. This tiny house duo are each a whopping 200sf. The bed is in its own nook, the rest of the space being open save for a bathroom. Therein is the difference. Wilsada has a narrow 4x6 bath while the A is a slightly more spacious 5x5. Otherwise the plans are very similar with their multitude of windows.
The Cottage in the Grove C2042 was a joint project with our builder friend last year. We finally got around to creating the artwork and writing the text for this one. This was a narrow 1356sf house that has the most charm of any of our offerings yet. Two suites each with bathrooms and a large open downstairs space.
The Houston A 2448A steps in with a slightly larger footprint than his predecessor. The numbering belies his true width of 25'. Other than an even 1200sf, not much changed from the prior version. The roof line was modified to maintain the 16' roof plane.
Three Edgewoods were finally put on display. A few years ago we spent alot of time with the original version creating several spin offs for our builder friend. The Edgewood C C2552C and The Edgewood D C2552D offer variations on the 25'-28' wide 3 bed 2 bath story-and-a-half theme. Rounding out the triad is the The Edgewood D2 C2552D-2 mashup. Not only is it a lot of width, it's also a lot of characters in the numerical coding!
Finally is a brand new plan inspired from a century ago. The Arleta 2850 adds a third true single story full size plan to our lineup (right behind the Houstons). At only 1353sf, this little charmer is guaranteed to be a winner in the new downsized home movement. Three beds, two baths, lots of closets, and both material and energy efficiency just enforce her future position in the marketplace. We're very excited about this one and hope to see it built soon.
Check out our full catalog for all plans.
The Wilsada A 1416A joins her brother the Wilsada 1416. This tiny house duo are each a whopping 200sf. The bed is in its own nook, the rest of the space being open save for a bathroom. Therein is the difference. Wilsada has a narrow 4x6 bath while the A is a slightly more spacious 5x5. Otherwise the plans are very similar with their multitude of windows.
The Cottage in the Grove C2042 was a joint project with our builder friend last year. We finally got around to creating the artwork and writing the text for this one. This was a narrow 1356sf house that has the most charm of any of our offerings yet. Two suites each with bathrooms and a large open downstairs space.
The Houston A 2448A steps in with a slightly larger footprint than his predecessor. The numbering belies his true width of 25'. Other than an even 1200sf, not much changed from the prior version. The roof line was modified to maintain the 16' roof plane.
Three Edgewoods were finally put on display. A few years ago we spent alot of time with the original version creating several spin offs for our builder friend. The Edgewood C C2552C and The Edgewood D C2552D offer variations on the 25'-28' wide 3 bed 2 bath story-and-a-half theme. Rounding out the triad is the The Edgewood D2 C2552D-2 mashup. Not only is it a lot of width, it's also a lot of characters in the numerical coding!
Finally is a brand new plan inspired from a century ago. The Arleta 2850 adds a third true single story full size plan to our lineup (right behind the Houstons). At only 1353sf, this little charmer is guaranteed to be a winner in the new downsized home movement. Three beds, two baths, lots of closets, and both material and energy efficiency just enforce her future position in the marketplace. We're very excited about this one and hope to see it built soon.
Check out our full catalog for all plans.
Thursday, December 8, 2011
Our Technological Toolbelt
Contractors carry a toolbelt (or drive a truck) full of useful tools for building a house. We at Istockhouseplans wear a little different utility apparel. Ours is less physical and a little more electronic. In fact it weighs hardly anything at all (which makes us quite portable without an F-350).
The most important tool we use is AutoCAD LT. Without a digital drafting tool, we would be relegated to the physical tools of our forebears, that of a pencil and triangle. Though be not deceived. We have a great respect for those that still practice this dying art. AutoCAD can be a little spendy for the weekend warrior. The LT version is slowly approaching $1000 in price while the full version can be $4000 or more.
If you're just looking for a cheap tool that can still get the job done, we recommend A9CAD. This free tool has all of the functionality we need except for colortables. If we didn't have to print pretty pictures, we'd probably be using it.
DoubleCAD is another free product that has much more functionality, about as much as AutoCAD itself. The look and feel is a little different. DraftSight is another program we've found that almost perfectly replicates AutoCAD. It does tend to have a bit of a lag though.
Sometimes we'll play with 3-D imaging. Rather than pay the several thousand dollars to get the full version of AutoCAD, we've found the ever popular SketchUp from Google. Sketchup is clean, intuitive, and (like AutoCAD) has several different ways to do the same thing. We've found the basic version to be enough for our needs though we sometimes crunch the numbers to see if we could afford the $500 upgrade to Pro. Pro allows more functions including creating your own Dynamic Components. This means you don't have to create a 2x4, 2x6, 2x8, etc. You just create a joist and then before you insert, drop down menus allow you to choose width, height and length.
When you order a paper plan from us, we send the file to the printshop as pre-printed PDF sheets. They print the PDF sheets, bind them, and your plans are born. There are several ways to create a PDF. We've tried a few and the best one we've found is CutePDF. This application installs like a printer in your computer system. When you're ready to create a PDF from any program, go to print, and then select CutePDF as your printer. A myriad of paper sizes are available.
The images of our plans that are posted on the website are created through a two-step process. Unfortunately the quality of jpg and png that AutoCAD spits out are unacceptable. We've found that we get much better quality from a pdf. So we'll print the pdf (as mentioned above) and then open it up and export a jpg or png from the image.
Sometimes we'll further manipulate these images to get the size and contrast we want. For this we use Irfanview. Irfanview is another free program that does a bang-up job of manipulating image files. We have used it to crop images, manipulate size and resolution, glue images together and much more.
Our images are then uploaded to Picasa Web Albums by Google. The images on our website are referenced from Picasa as static images. You can link to your images so that they are clickable or not, have a border or not, and control the size that the viewer sees.
Our blog is hosted by Blogger, another Google company. The decision to use Blogger was merely one of convenience. Rather than have several different log-ins for several different web portals, we decided to keep everything with Google that we could.
To continue the Google theme (maybe we oughta buy stock?) we use Checkout for our shopping cart, Analytics to get a look at our pageview trends, Docs to create release letters, and Maps for our mapplet.
Our website was created with Google Page Creator. We were very pleased with the look we had built. A couple of years ago Google decided to close out Page Creator in favor of a program called Sites. Our website was converted to the new look and looked just awful. So we downloaded our coding from Page Creator and had it hosted privately. This has worked well but it means that when a change needs to be made that we have to manually log in and make the coding change ourselves. A small price to pay for having that much control.
Our website is now hosted on Go Daddy. We switched to GoDaddy several years ago after reviewing their pricing structure. They really are one of the lowest price options out there. The few times we've needed their customer service we had no problems. Full disclosure: Istockhouseplans will get a little kickback if you click on and purchase products through any of the following links. If you want to get $5.99 domains, $1.99/mo web hosting, or SSL certificates, at least check them out.
(All other programs listed are of our own free will and we get no benefits whatsoever).
The most important tool we use is AutoCAD LT. Without a digital drafting tool, we would be relegated to the physical tools of our forebears, that of a pencil and triangle. Though be not deceived. We have a great respect for those that still practice this dying art. AutoCAD can be a little spendy for the weekend warrior. The LT version is slowly approaching $1000 in price while the full version can be $4000 or more.
If you're just looking for a cheap tool that can still get the job done, we recommend A9CAD. This free tool has all of the functionality we need except for colortables. If we didn't have to print pretty pictures, we'd probably be using it.
DoubleCAD is another free product that has much more functionality, about as much as AutoCAD itself. The look and feel is a little different. DraftSight is another program we've found that almost perfectly replicates AutoCAD. It does tend to have a bit of a lag though.
Sometimes we'll play with 3-D imaging. Rather than pay the several thousand dollars to get the full version of AutoCAD, we've found the ever popular SketchUp from Google. Sketchup is clean, intuitive, and (like AutoCAD) has several different ways to do the same thing. We've found the basic version to be enough for our needs though we sometimes crunch the numbers to see if we could afford the $500 upgrade to Pro. Pro allows more functions including creating your own Dynamic Components. This means you don't have to create a 2x4, 2x6, 2x8, etc. You just create a joist and then before you insert, drop down menus allow you to choose width, height and length.
When you order a paper plan from us, we send the file to the printshop as pre-printed PDF sheets. They print the PDF sheets, bind them, and your plans are born. There are several ways to create a PDF. We've tried a few and the best one we've found is CutePDF. This application installs like a printer in your computer system. When you're ready to create a PDF from any program, go to print, and then select CutePDF as your printer. A myriad of paper sizes are available.
The images of our plans that are posted on the website are created through a two-step process. Unfortunately the quality of jpg and png that AutoCAD spits out are unacceptable. We've found that we get much better quality from a pdf. So we'll print the pdf (as mentioned above) and then open it up and export a jpg or png from the image.
Sometimes we'll further manipulate these images to get the size and contrast we want. For this we use Irfanview. Irfanview is another free program that does a bang-up job of manipulating image files. We have used it to crop images, manipulate size and resolution, glue images together and much more.
Our images are then uploaded to Picasa Web Albums by Google. The images on our website are referenced from Picasa as static images. You can link to your images so that they are clickable or not, have a border or not, and control the size that the viewer sees.
Our blog is hosted by Blogger, another Google company. The decision to use Blogger was merely one of convenience. Rather than have several different log-ins for several different web portals, we decided to keep everything with Google that we could.
To continue the Google theme (maybe we oughta buy stock?) we use Checkout for our shopping cart, Analytics to get a look at our pageview trends, Docs to create release letters, and Maps for our mapplet.
Our website was created with Google Page Creator. We were very pleased with the look we had built. A couple of years ago Google decided to close out Page Creator in favor of a program called Sites. Our website was converted to the new look and looked just awful. So we downloaded our coding from Page Creator and had it hosted privately. This has worked well but it means that when a change needs to be made that we have to manually log in and make the coding change ourselves. A small price to pay for having that much control.
Our website is now hosted on Go Daddy. We switched to GoDaddy several years ago after reviewing their pricing structure. They really are one of the lowest price options out there. The few times we've needed their customer service we had no problems. Full disclosure: Istockhouseplans will get a little kickback if you click on and purchase products through any of the following links. If you want to get $5.99 domains, $1.99/mo web hosting, or SSL certificates, at least check them out.
(All other programs listed are of our own free will and we get no benefits whatsoever).
Tuesday, December 6, 2011
Energy Efficient Wall Systems
You may remember our post a couple of years ago promoting Fat Walls. In their 11/11 monthly newsletter, Energy Design Update recently reported on 15 different wall assemblies modeled through TRNSYS software. The walls were simulated in the climates typical to Atlanta, Pittsburgh, and Phoenix. Of the 15 walls, three tied in first place for an overall value of R-43. One of these walls fills a 2x6 cavity with closed cell polyurethane spray foam for a rather high price tag. The second wall involves 10" thick SIPS. The third wall is our option number four from the previously mentioned post with 2" more of foam. That is, a 2x6 wall with blow-in and 4" of outboard XPS foam. As we mentioned back when we wrote the initial post, this makes window detailing a bit of a bear. Attachment issues come into play as well. The advantage of this system is the standard wall framing and no loss of floor space inside the house.
A reasonable compromise might be 3" of foam. This allows the use of true 2x4 for bucking out windows while allowing 1/2" air space. Half inch furring strips can then be used over the foam for attachment as well as a rainscreen.
They also modeled a similar wall as our top choice, double 2x4, total 8" thick with 2" of outboard foam. Our results? R-40 with U-0.20 windows. Their results were R-38 with U-0.25 windows. As you should know, U-0.20 windows are slightly better than U-0.25 resulting in a slightly higher total wall R-value.
So apparently we know what we're doing!
A reasonable compromise might be 3" of foam. This allows the use of true 2x4 for bucking out windows while allowing 1/2" air space. Half inch furring strips can then be used over the foam for attachment as well as a rainscreen.
They also modeled a similar wall as our top choice, double 2x4, total 8" thick with 2" of outboard foam. Our results? R-40 with U-0.20 windows. Their results were R-38 with U-0.25 windows. As you should know, U-0.20 windows are slightly better than U-0.25 resulting in a slightly higher total wall R-value.
So apparently we know what we're doing!
Tuesday, November 22, 2011
New Tiny House Plan
We at Istockhouseplans have been busy developing a cadre of tiny house plans. Not every one makes the cut to be web-worthy. Most of them do however become inspiration for other plans. We are proud to introduce our latest plan, the Wilsada 1416.
Several things inspired this plan. One was simple lines. The plan is a simple box with one tip out and three ridges. Generous light also came into play. A sliding glass door provides entry on one side while a bank of windows opens up a view on another side. The third was tiny bathrooms. We first introduced a complete wet room in the Carver cabin series. We continue the idea in the Wilsada. Finally, we have been recently enamored with the idea of sleeping nooks. Rather than a formal bedroom, the Wilsada contains a very cozy bed nook. Visualize curtains over the opening and a little bookcase at the foot. And of course it's elevated allowing for storage underneath.
A kitchenette, sitting porch, and vaulted ceiling complete the look. Despite our generally craftsman motifs, we could easily see this one decked in white beadboard. Somewhat of an East Coast beach theme. Probably not appropriate for a mountain retreat. Or maybe that's just the kind of irony that you go for.
Several things inspired this plan. One was simple lines. The plan is a simple box with one tip out and three ridges. Generous light also came into play. A sliding glass door provides entry on one side while a bank of windows opens up a view on another side. The third was tiny bathrooms. We first introduced a complete wet room in the Carver cabin series. We continue the idea in the Wilsada. Finally, we have been recently enamored with the idea of sleeping nooks. Rather than a formal bedroom, the Wilsada contains a very cozy bed nook. Visualize curtains over the opening and a little bookcase at the foot. And of course it's elevated allowing for storage underneath.
A kitchenette, sitting porch, and vaulted ceiling complete the look. Despite our generally craftsman motifs, we could easily see this one decked in white beadboard. Somewhat of an East Coast beach theme. Probably not appropriate for a mountain retreat. Or maybe that's just the kind of irony that you go for.
Tuesday, November 8, 2011
IKEA Loves Small Homes
If you've received your copy of the 2012 IKEA catalog, you may have noticed a theme. We at Istockhouseplans were thrilled to read the phrase on the front: "A HOME DOESN'T NEED TO BE BIG, JUST SMART." Bravo IKEA, bravo!
The first couple of pages immediately show some ideas that the IKEA design team put together. They created a space for 6 friends to live in within 430 square feet. The solution consists of curtained bunkbeds at the edge with a large table in the middle. All other space is communal.
Their second challenge was a 75 square foot kitchen. IKEA was able to get an island and plenty of storage in the small space. Other layouts are shown starting on page 112. If these still aren't inspiration enough, you can go to IKEA's website and use their kitchen design software.
The next challenge was a 118 square foot living-slash-bedroom-slash-playroom. The central feature is a loft bed for the grown-ups. Another variation is shown in a 107 square foot living room that is essentially a showcase room for a chaise lounge.
The final design involves a 29 square foot bathroom - with laundry space and a spa tub. There must be some smoke and mirrors here because no good ol' 'Merican spa tub would be less than 29sf itself, right?
To see videos showcasing all of these ideas, visit IKEA-USA.com/smallspaces.
The coup de grace of all of this for us was the new Lillangen single bowl sink. One of our favorite things is to make secondary rooms (powder baths especially) as small as possible. Building code dictates some minimum sizes needed around fixtures. At some point to get smaller, the fixtures need to shrink. We can specify a smaller sink only to have the contractor turn it down because of cost. (Why are smaller appliances, fixtures, and doodads so much more expensive anyway?) IKEA's previously mentioned sink is less than 11" in depth with a side faucet (faucet sold separately). Price for the ceramic, $49.99. Price for faucets starting at $39.99. Less than $100 to reduce the size of the house, or give that space to another use.
Of course this is all good news for our line of tiny homes. If you try to design a tiny home as a mini-McMansion you will fail. But with IKEA and a little ingenuity you can make anything happen.
*Full disclosure: IKEA has no idea I wrote this blog post.
The first couple of pages immediately show some ideas that the IKEA design team put together. They created a space for 6 friends to live in within 430 square feet. The solution consists of curtained bunkbeds at the edge with a large table in the middle. All other space is communal.
Their second challenge was a 75 square foot kitchen. IKEA was able to get an island and plenty of storage in the small space. Other layouts are shown starting on page 112. If these still aren't inspiration enough, you can go to IKEA's website and use their kitchen design software.
The next challenge was a 118 square foot living-slash-bedroom-slash-playroom. The central feature is a loft bed for the grown-ups. Another variation is shown in a 107 square foot living room that is essentially a showcase room for a chaise lounge.
The final design involves a 29 square foot bathroom - with laundry space and a spa tub. There must be some smoke and mirrors here because no good ol' 'Merican spa tub would be less than 29sf itself, right?
To see videos showcasing all of these ideas, visit IKEA-USA.com/smallspaces.
The coup de grace of all of this for us was the new Lillangen single bowl sink. One of our favorite things is to make secondary rooms (powder baths especially) as small as possible. Building code dictates some minimum sizes needed around fixtures. At some point to get smaller, the fixtures need to shrink. We can specify a smaller sink only to have the contractor turn it down because of cost. (Why are smaller appliances, fixtures, and doodads so much more expensive anyway?) IKEA's previously mentioned sink is less than 11" in depth with a side faucet (faucet sold separately). Price for the ceramic, $49.99. Price for faucets starting at $39.99. Less than $100 to reduce the size of the house, or give that space to another use.
Of course this is all good news for our line of tiny homes. If you try to design a tiny home as a mini-McMansion you will fail. But with IKEA and a little ingenuity you can make anything happen.
*Full disclosure: IKEA has no idea I wrote this blog post.
Tuesday, October 25, 2011
Calculating Even More Heat Load
Welcome back to the third and final installment of calculating heat load. In Part I we looked at the envelope of the home. In Part II we looked at air infiltration and how it works. In this part we will look at internal loads and finally deciding what heat source to add to a home.
We realized that we should have been giving a real world example from the start. In light of that, let's do some quick review using our plan The Belmont #3232. If you recall the equations:
For air infiltration, recall the formula ΔT x ACHnat x Volume x HC = BTU/hr. Our ΔT=45°F, volume is 18432 (32x32x18), HC = 0.022, and we'll assume ACHnat to be based off of a blower door test of 5.0ACH, ergo .25.
Now for the good news! You will have several internal loads that will help to heat your house, that is, they will make this number smaller. The biggest source is the occupants. General convention assumes that there will be 2 people in the master bedroom and one person for each of the other bedrooms. The Belmont is a 4 bedroom home but practically we could assume four occupants living upstairs. Occupants put out anywhere from 200 to 300 btu/hr of heat load. We are preferential towards 275 btu/hr. For four people, this is a reduction of 1100 btu/hr. You can also figure in incandescent lights, the kitchen oven, hair dryers and other such pieces. These don't make a huge difference unless your heat load is so low that you are in PassivHaus range.
Our final result for heating this home in this scenario is 14861.52 btu/hr. Now what? Now we need a heat source. Our first choice might be the typical forced air gas furnace. A quick look at manufacturer catalogs will reveal that 40,000 btu/hr is the smallest one available. Even at a low 90% efficiency this will put out 36,000 btu/hr. But if you have an attached garage, you can always place the furnace there and lose about 40% of your heat bringing the load down to about 25,700 btu/hr. Let's not.
Another option might be electric wall heaters. Each 1kW wall heater = 3412 btu/hr. This calculates to needing 5 heaters. Reviewing this plan shows that there are up to 10 rooms that would need heat. Perhaps several 500W units would be more applicable. Don't forget to install them on an interior wall.
Another choice is a ductless heat pump. You are limited to a max of 4 heads per unit. More heads requires another unit which doubles the price. Or you could get a splitter for some of the heads and share the heat load between rooms. To outfit the Belmont 3232 you would need one head for the dining/parlor, one split head for the office/bath, another for the master and bath, one more for the auxiliary bedrooms. The kitchen, utility room and bathroom would need a 500W electric heat source.
Another option might be radiant heat. In floor hydronic heat puts out 18-25 btu/sf. Assuming 20btu, you could cover 743sf of the floor with tubing. But how do you cover 743sf in a 2000sf house? If you stick to just the walk areas you could make it happen. But unless you are doing an onsite DIY approach, this option can be super expensive.
The final choice would be to increase some insulation in the walls, try for better windows (U-0.025 is reasonable) and tighten the home to 2.0 ACH or less. Resulting calculations reduces to 10519 btu/hr. Then install an HRV in the utility room to cycle fresh air and attach a small heating unit to it.
Any other ideas?
In the very near future we'll refine our simple spreadsheet calculator and make it available for your use. The calculator does most of the math for you but we made this guide available so you'd know what's going on in the background. Happy calculating!
We realized that we should have been giving a real world example from the start. In light of that, let's do some quick review using our plan The Belmont #3232. If you recall the equations:
- Afloor x Ufloor x ΔTfloor = Btu/hr floor
- Awall x Uwall x ΔTwall = Btu/hr wall
- Aceil x Uceil x ΔTceil = Btu/hr ceil
- Awindows x Uwindows x ΔTwindows = Btu/hr windows
- Adoor x Udoor x ΔTdoor = Btu/hr door
- Floors: (32x32) x (1/38) x 25°F = 673.68 (1024sf insulated floor, R-38 in joists)
- Walls: (32x18x4 - 339.33) x (1/21*.8) x 45°F = 5262.51 (four walls minus windows, 32'L x 18'H, R-21 with framing factor)
- Ceiling: (32x32) x (1/49*.8) x 25°F = 522.45 (1024sf ceiling, R-49 with framing factor due to edge pinch)
- Windows: 339.33 x 0.30 x 45°F = 4580.96
- Doors: 40 x 0.20 x 45°F = 360
For air infiltration, recall the formula ΔT x ACHnat x Volume x HC = BTU/hr. Our ΔT=45°F, volume is 18432 (32x32x18), HC = 0.022, and we'll assume ACHnat to be based off of a blower door test of 5.0ACH, ergo .25.
- 45°F x .25 x 18432 x 0.022 = 4561.92
Now for the good news! You will have several internal loads that will help to heat your house, that is, they will make this number smaller. The biggest source is the occupants. General convention assumes that there will be 2 people in the master bedroom and one person for each of the other bedrooms. The Belmont is a 4 bedroom home but practically we could assume four occupants living upstairs. Occupants put out anywhere from 200 to 300 btu/hr of heat load. We are preferential towards 275 btu/hr. For four people, this is a reduction of 1100 btu/hr. You can also figure in incandescent lights, the kitchen oven, hair dryers and other such pieces. These don't make a huge difference unless your heat load is so low that you are in PassivHaus range.
Our final result for heating this home in this scenario is 14861.52 btu/hr. Now what? Now we need a heat source. Our first choice might be the typical forced air gas furnace. A quick look at manufacturer catalogs will reveal that 40,000 btu/hr is the smallest one available. Even at a low 90% efficiency this will put out 36,000 btu/hr. But if you have an attached garage, you can always place the furnace there and lose about 40% of your heat bringing the load down to about 25,700 btu/hr. Let's not.
Another option might be electric wall heaters. Each 1kW wall heater = 3412 btu/hr. This calculates to needing 5 heaters. Reviewing this plan shows that there are up to 10 rooms that would need heat. Perhaps several 500W units would be more applicable. Don't forget to install them on an interior wall.
Another choice is a ductless heat pump. You are limited to a max of 4 heads per unit. More heads requires another unit which doubles the price. Or you could get a splitter for some of the heads and share the heat load between rooms. To outfit the Belmont 3232 you would need one head for the dining/parlor, one split head for the office/bath, another for the master and bath, one more for the auxiliary bedrooms. The kitchen, utility room and bathroom would need a 500W electric heat source.
Another option might be radiant heat. In floor hydronic heat puts out 18-25 btu/sf. Assuming 20btu, you could cover 743sf of the floor with tubing. But how do you cover 743sf in a 2000sf house? If you stick to just the walk areas you could make it happen. But unless you are doing an onsite DIY approach, this option can be super expensive.
The final choice would be to increase some insulation in the walls, try for better windows (U-0.025 is reasonable) and tighten the home to 2.0 ACH or less. Resulting calculations reduces to 10519 btu/hr. Then install an HRV in the utility room to cycle fresh air and attach a small heating unit to it.
Any other ideas?
In the very near future we'll refine our simple spreadsheet calculator and make it available for your use. The calculator does most of the math for you but we made this guide available so you'd know what's going on in the background. Happy calculating!
Tuesday, October 18, 2011
Calculating More Heat Load
Last week we looked at how to calculate your heat load based on the envelope of your home. This week we'll take a look at air infiltration and the effect it can have on your home. The caveat should be given that the tighter you make your home, the more you should be concerned about vapor barriers, retarders, and other management. Indoor air quality also becomes a concern. We won't address these issues in this post.
Air infiltration is not something that can be assumed or calculated. Just as a nail can't be driven by estimation, it needs a tool. The most common tool used is a blower door. This is a device that attaches into your front door frame and accepts a large industrial fan. After closing all other doors and windows, the fan is turned on (generally pointing out) until it is removing 50 cubic feet per minute (CFM) from your home. Some places in the world aim for 25 CFM. For a visual, imagine 4 regulation basketballs. This is 1 cubic foot. So turning the blower door on to 50 CFM means that you are throwing 200 basketballs out your front door every minute (or more than 3 every second!)
Why in the world would you do this? A couple of reasons. First, this is a great opportunity to walk around your house with a smoke stick and see where air is leaking in. These are places that need to be plugged. Get your caulk, foam, whatever and fill it up.
Second, since there is diagnostic equipment hooked to the blower door, a technician can determine how much air will blow through your home on a windy day. The result is a standardized answer that can be used for comparison. Generally it is in the range of 0-20 air changes per hour (ACH). This means that with the blower door running, the volume of air in your home could be changed out 20 times an hour. Every 3 minutes you're getting new air. This air is coming from outside, the attic, the crawlspace, and the attached garage.
Most newer homes fall around 6 ACH50. Older homes will be much higher. It takes some determination to lower a new home from 6 ACH50. No one accidentally builds a tight home. With some simple effort we have seen homes approach 4 ACH50. A bit more effort and change in building methods results in 2 ACH50 which is very good. The lowest we've ever seen is 0.22 ACH50. This was a home built to PassivHaus standards.
So why does this matter for energy calculations? Warm air can be blown out of your home and replaced with cool winter air through leaks. We need to calculate for this for the furnace to be able to keep up. Otherwise your home will get cooler and cooler until it equalizes with the outdoors. This could occur with a 3000sf leaky home and a 40kBTU furnace. Bad news.
Less talking, more computing. This is one single formula that has a lot of lead up. There are four numbers in the formula. The first is our friend ΔT. The second is the result of your blower door test in ACH50. We need natural ACH so divide by 20. The third is the volume of your heated area. The fourth is the convective heat transfer co-efficient (HC). This number has a general range around 0.018 to 0.022:
ΔT x ACHnat x Volume x HC = BTU/hr
Example: A 1500sf house has a blower door result of 3.5ACH50. Assume HC to be 0.022 (Marine Cold). What is the heat loss through infiltration?
Answer: ΔT from last week is still 45°F. ACHnat = ACH50/20 which is 3.5/20 = 0.175. Volume is approximately 1500sf x 9' (ceilings) = 13500cf. HC is stated. So the formula is 45 x 0.175 x 13500 x 0.022 = 2339 BTU/hr. Note that we gave a tightness that is half of typical. Were it 7 ACH50 this load would double! Don't think air tightness matters? It's the biggest factor in heat load.
Add this to your envelope load and come back next week for part three, Interior Loads!
Air infiltration is not something that can be assumed or calculated. Just as a nail can't be driven by estimation, it needs a tool. The most common tool used is a blower door. This is a device that attaches into your front door frame and accepts a large industrial fan. After closing all other doors and windows, the fan is turned on (generally pointing out) until it is removing 50 cubic feet per minute (CFM) from your home. Some places in the world aim for 25 CFM. For a visual, imagine 4 regulation basketballs. This is 1 cubic foot. So turning the blower door on to 50 CFM means that you are throwing 200 basketballs out your front door every minute (or more than 3 every second!)
Why in the world would you do this? A couple of reasons. First, this is a great opportunity to walk around your house with a smoke stick and see where air is leaking in. These are places that need to be plugged. Get your caulk, foam, whatever and fill it up.
Second, since there is diagnostic equipment hooked to the blower door, a technician can determine how much air will blow through your home on a windy day. The result is a standardized answer that can be used for comparison. Generally it is in the range of 0-20 air changes per hour (ACH). This means that with the blower door running, the volume of air in your home could be changed out 20 times an hour. Every 3 minutes you're getting new air. This air is coming from outside, the attic, the crawlspace, and the attached garage.
Most newer homes fall around 6 ACH50. Older homes will be much higher. It takes some determination to lower a new home from 6 ACH50. No one accidentally builds a tight home. With some simple effort we have seen homes approach 4 ACH50. A bit more effort and change in building methods results in 2 ACH50 which is very good. The lowest we've ever seen is 0.22 ACH50. This was a home built to PassivHaus standards.
So why does this matter for energy calculations? Warm air can be blown out of your home and replaced with cool winter air through leaks. We need to calculate for this for the furnace to be able to keep up. Otherwise your home will get cooler and cooler until it equalizes with the outdoors. This could occur with a 3000sf leaky home and a 40kBTU furnace. Bad news.
Less talking, more computing. This is one single formula that has a lot of lead up. There are four numbers in the formula. The first is our friend ΔT. The second is the result of your blower door test in ACH50. We need natural ACH so divide by 20. The third is the volume of your heated area. The fourth is the convective heat transfer co-efficient (HC). This number has a general range around 0.018 to 0.022:
ΔT x ACHnat x Volume x HC = BTU/hr
Example: A 1500sf house has a blower door result of 3.5ACH50. Assume HC to be 0.022 (Marine Cold). What is the heat loss through infiltration?
Answer: ΔT from last week is still 45°F. ACHnat = ACH50/20 which is 3.5/20 = 0.175. Volume is approximately 1500sf x 9' (ceilings) = 13500cf. HC is stated. So the formula is 45 x 0.175 x 13500 x 0.022 = 2339 BTU/hr. Note that we gave a tightness that is half of typical. Were it 7 ACH50 this load would double! Don't think air tightness matters? It's the biggest factor in heat load.
Add this to your envelope load and come back next week for part three, Interior Loads!
Tuesday, October 11, 2011
Calculating Heat Load
How many times have you looked at a house plan or a house and wondered how much heat it was going to use per year, or need at peak times? There are several good programs out there that will allow you to do this with a few mouse clicks. Maybe you don't have access to such a program and want to make an educated guess. There are several simple calculations that you can do to figure out the answer.
What we are figuring out is the amount of heat that is lost from the house in several ways. One way is by conduction through the envelope. Another way is by convection through leaks in the house. Most factors are known but several need to be looked up. Once you know those values for your area, you can use them again and again.
Let's establish those values. First you will need to establish your highest desired indoor temperature. During winter this might be 62°F or 65°F or 68°F. We'll use 65°F for this guide. Next you'll want to establish the coldest outdoor temperature that might be experienced. For the walls this might be 20°F or 0°F or -20°F if you're in Alaska. We'll assume 20°F for this guide.
Beware however that your crawlspace and attic will have different cold temperatures. If your insulation is in the ceiling plane instead of the roof plane, your attic will enjoy the comfort of being enclosed even though it won't be insulated. Therefore in 20°F weather the attic may register at 40°F. The same situation is present in the crawl space, especially if it's vented and any walls adjacent to a garage. We'll use 40°F for these three locations.
Using these temperatures establish a difference of temperature known as ΔT (delta-T). This is simply subtracting the coldest outside temperature from the desired indoor temperature. Using our established values the walls, windows, and exterior doors will have a ΔT of 45°F and the crawl space and attic will have a ΔT of 25°F.
Next you'll need to gather the areas of each of the parts of your building envelope. This includes floors, walls, ceilings, windows, and doors. Rather than figure the exact wall area, imagine there are no windows or doors. Then when you do the window and door areas, you can subtract them from the wall area to get a more accurate reading with less calculation. If you want to be especially precise, you can note the amount of wall against the garage, second floor walls against first floor attics, etc. We'll skip that precision.
The other thing you'll need to gather is the U-value of those components. U-value is the inverse of R-value. U-value should also take into account the whole assembly and not just the insulation itself. An R-21 batt does not equal an R-21 wall. A typical R-21 wall will end up at about R-16, that is, a U-value of 1/16 or .0625. A simple true R-value conversion can be had by multiplying your insulation R-value by a factor depending on quality. For a standard average build, assume 75% of your insulation value. For good construction (24" o.c. R-30 wall for example) assume 80%. If you're using exterior foam, figure your percentage value and then add the foam. For instance, an average R-21 wall works out to about R-16 but adding 1-1/2" of XPS foam adds R-7.5 for a total of R-23.5, U-value of .0426. More precision is better but don't go crazy.
Let's put it all together:
The general equation for each element is area x u-value x ΔT. You should write down the following:
Next week: Infiltration!
What we are figuring out is the amount of heat that is lost from the house in several ways. One way is by conduction through the envelope. Another way is by convection through leaks in the house. Most factors are known but several need to be looked up. Once you know those values for your area, you can use them again and again.
Let's establish those values. First you will need to establish your highest desired indoor temperature. During winter this might be 62°F or 65°F or 68°F. We'll use 65°F for this guide. Next you'll want to establish the coldest outdoor temperature that might be experienced. For the walls this might be 20°F or 0°F or -20°F if you're in Alaska. We'll assume 20°F for this guide.
Beware however that your crawlspace and attic will have different cold temperatures. If your insulation is in the ceiling plane instead of the roof plane, your attic will enjoy the comfort of being enclosed even though it won't be insulated. Therefore in 20°F weather the attic may register at 40°F. The same situation is present in the crawl space, especially if it's vented and any walls adjacent to a garage. We'll use 40°F for these three locations.
Using these temperatures establish a difference of temperature known as ΔT (delta-T). This is simply subtracting the coldest outside temperature from the desired indoor temperature. Using our established values the walls, windows, and exterior doors will have a ΔT of 45°F and the crawl space and attic will have a ΔT of 25°F.
Next you'll need to gather the areas of each of the parts of your building envelope. This includes floors, walls, ceilings, windows, and doors. Rather than figure the exact wall area, imagine there are no windows or doors. Then when you do the window and door areas, you can subtract them from the wall area to get a more accurate reading with less calculation. If you want to be especially precise, you can note the amount of wall against the garage, second floor walls against first floor attics, etc. We'll skip that precision.
The other thing you'll need to gather is the U-value of those components. U-value is the inverse of R-value. U-value should also take into account the whole assembly and not just the insulation itself. An R-21 batt does not equal an R-21 wall. A typical R-21 wall will end up at about R-16, that is, a U-value of 1/16 or .0625. A simple true R-value conversion can be had by multiplying your insulation R-value by a factor depending on quality. For a standard average build, assume 75% of your insulation value. For good construction (24" o.c. R-30 wall for example) assume 80%. If you're using exterior foam, figure your percentage value and then add the foam. For instance, an average R-21 wall works out to about R-16 but adding 1-1/2" of XPS foam adds R-7.5 for a total of R-23.5, U-value of .0426. More precision is better but don't go crazy.
Let's put it all together:
The general equation for each element is area x u-value x ΔT. You should write down the following:
- Afloor x Ufloor x ΔTfloor = Btu/hr floor
- Awall x Uwall x ΔTwall = Btu/hr wall
- Aceil x Uceil x ΔTceil = Btu/hr ceil
- Awindows x Uwindows x ΔTwindows = Btu/hr windows
- Adoor x Udoor x ΔTdoor = Btu/hr door
Next week: Infiltration!
Tuesday, September 27, 2011
Istockhouseplans Gets Greener
As more and more companies are beginning to do a life cycle analysis of their products, Istockhouseplans feels that this is a worthwhile study to pursue. Generally we will send you a half dozen sets of plans. Most of those will go to the permitting jurisdiction for approval; some of those you will give out to subs to do their work. What's left is a few sets around the jobsite that get muddy, or a couple extra sets that get stuck under the seat of your F-350. We've compiled this list of how you can safely, humanely, and environmentally end the life of those plans.
Other ideas? Please feel free to share in the comments. Want to employ some of these ideas yourself? Visit our plan catalog and purchase your own set.
- Recycle them in the paper bin. Duh.
- Ship them back to us for proper disposal.
- Shred them for landscaping mulch.
- Shred them for attic insulation.
- Shred them for party confetti.
- Sweep up your wood dust and roll it up into a set of plans. Smash the ends in and leave a few next to the woodstove or outdoor fireplace for the new homeowner to burn.
- If you have a nice set leftover, present them to the homeowner. Possibly even in a frame. Or take the time to mount them over the fireplace yourself. Build the frame out of scrap wood from the site.
- If a set gets too muddy to use, wrinkle it up good, re-flatten it and set it in front of an exterior door for a shoe mat.
- Cut strips to use if you run out of drywall tape.
- Separate the sheets and fold them into origami for the children who are pressing their faces into your cyclone fence.
- Let your kids color the elevations.
- Use the backs as large blank sheets for your kids to color on.
- Make holiday cards for your subs/supers/suppliers using the elevations or details as the front picture.
Other ideas? Please feel free to share in the comments. Want to employ some of these ideas yourself? Visit our plan catalog and purchase your own set.
Wednesday, September 14, 2011
Lumber Sizes
Ever notice that a 2x4 isn't really 2"x4"? What's with that? Fact is that the piece of wood started at 2"x4" but is called "rough sawn", that is it has unfinished faces. The stick is then sent through a planer to smooth the faces and reduce serious splinter casualties. About 1/4" is shaved off of each of the four faces resulting in a lesser dimension than you would expect. Besides, who would want to say "one-and-a-half by three-and-a-half"? Mind the twist at 2x8 and beyond...
Now pay attention as we mention dimension convention:
1x:
And while we're at it, how about some typical engineered wood sizes.
I-joists are created by standing a piece of OSB or plywood upright and capping it with a 2x flange. The result looks like a capital serif 'I' hence the name.
I-joist flange widths (varies by manufacturer):
LVL widths:
Glu-lam beams are created by gluing and compressing several layers of post milled dimensional lumber together. The whole beam is then planed again to create an even surface. For this reason, glu-lam beams are slightly narrower than dimensional lumber. Heights are always in multiples of 1-1/2" due to the size of the plies. Due to general engineering practice the height should always exceed the width though rare exceptions always exist.
Glu-lam widths:
Now pay attention as we mention dimension convention:
1x:
- 1x2 = .75" x 1.5"
- 1x3 = .75" x 2.5"
- 1x4 = .75" x 3.5"
- 1x6 = .75" x 5.5"
- 2x2 = 1.5" x 1.5"
- 2x3 = 1.5" x 2.5"
- 2x4 = 1.5" x 3.5"
- 2x6 = 1.5" x 5.5"
- 2x8 = 1.5" x 7.25"
- 2x10 = 1.5" x 9.25"
- 2x12 = 1.5" x 11.25"
- 2x14 = 1.5" x 13.25"
- 3x4 = 2.5" x 3.5"
- 3x6 = 2.5" x 5.5"
- 4x4 = 3.5" x 3.5"
- 4x6 = 3.5" x 5.5"
- 4x8 = 3.5" x 7.25"
- 4x10 = 3.5" x 9.25"
- 4x12 = 3.5" x 11.25"
- 4x14 = 3.5" x 13.25"
And while we're at it, how about some typical engineered wood sizes.
I-joists are created by standing a piece of OSB or plywood upright and capping it with a 2x flange. The result looks like a capital serif 'I' hence the name.
I-joist flange widths (varies by manufacturer):
- 1-3/4"
- 2"
- 2-5/16"
- 3-1/2"
- 9-1/2"
- 11-7/8"
- 14"
- 16"
- 18"
- 20"
- 22"
- 24"
LVL widths:
- 1-3/4" (2 layers)
- 2-5/8" (3 layers)
- 3-1/2" (4 layers)
- 5-1/4" (6 layers)
- 7" (8 layers)
- Any height possible though generally intended to match I-joist material. Can match dimensional as well.
Glu-lam beams are created by gluing and compressing several layers of post milled dimensional lumber together. The whole beam is then planed again to create an even surface. For this reason, glu-lam beams are slightly narrower than dimensional lumber. Heights are always in multiples of 1-1/2" due to the size of the plies. Due to general engineering practice the height should always exceed the width though rare exceptions always exist.
Glu-lam widths:
- 3-1/8"
- 5-1/8"
- 6-3/4"
- 8-3/4"
- 10-3/4"
- 6"
- 7.5"
- 9"
- 10.5"
- 12"
- 13.5"
- 15"
- 16.5"
- 18"
- 19.5"
- 21"
- etc...
Subscribe to:
Posts (Atom)
Posts
