3.20.2010
The wife and I were lucky enough to close on a mid-century modern house in Dallas last summer. The house was built in 1953 and has a pretty progressive design with lots of south facing windows with large eves so there is little or no solar gain in the summer. That combined with the large trees in the back yard helped keep our power bills below $200 for most of the summer ( $0.10 per sq ft per month). That was all fine and good until this winter which was the 8th coldest on record. A previous genius owner has switched from gas heat to electric so our once quaint electric bills peaked at $527 ($0.27per /sq ft) in February. After our first large bill in December I began to look for ways to save some money on heating. I first caulked every open crack and weather stripped all of the windows and doors. That didn't help too much so I began to look at replacement windows. The original windows are all single pane glass with every room having at least one aluminum sliding window. After some reading on the internet I discovered that single pane aluminum are the most inefficient types of frames. I looked at replacement windows but to keep the feel of the house was going to cost a ton of money. All of our windows are not of standard size and many have weird angles. This means that each replacement window would have to be custom ordered at $500 to $1000 a pop for double pane windows. I was guessing that it was going to cost $10,000 to replace all 10 of the windows in the master bedroom including instillation. That was too much for one room so I kept on searching online and found this company Window-Therm that makes these things called Advanced Energy Panels (AEP). These are window panels that add insulation over your existing windows. They cost between $50 and $130 dollars per window up to sizes 48x84".The marketing on the site says that it will increase the R factor of a typical single pane window from 1.1 to 3.4, or U-factor from 1.25 to 0.29. This sounded pretty good to me. So I ordered a few of them to try them out. The panels arrived in kits several weeks after I ordered them. I consider myself a pretty handy guy and this ended up being a sizable project taking up 10 hours over three weekends to install 10 panes. To be fair, the process would have been much faster if I had chosen to "surface mount" the panels instead of "recess mount" the panels. The surface mount is more forgiving of inaccurate measurements and does not require stops. Of course the surface mount was not as pleasing to my eye as the recess mount. Also it took a lot of time to figure out the how to get a good fit for the three panels that were rhomboid in shape (i.e. the top of the pane at a 7 degree slope) which requires some careful miter saw work and bending the corner pieces. As of today all of the panel frames are built. 6 of them have been stretched with the polyolefin film on both sides. This process was a lot easier that I thought and the panels look good. I still have a few more of the panels to stretch and I have to buy (and paint) some more stops. I wanted to get some of the panes up with dry fitted stops because a cold front was moving in toady and it was supposed to snow. After the temperature dropped I did some test readings to see how well the panels performed. Of course the true test will be the next power bill!
My tips for saving time when installing:
1. Don't use a hack saw unless you are only putting up one or two panels. Miter saw is the way to go.
2. Buy the expensive metal blade for your saw. The $5 blade didn't cut well and got so hot it melted some of the plastic bits on my new saw . I used a $14 Diablo demolition blade (#DO724DR )and it worked great.
3. For recessed mounting measure the opening and cut the frame and the stops at the same time. I didn't do this and it is now a pain to go back and re-measure everything.
4. For larger windows you will need a cross brace (mutin) as the film pulls in and bends the frame a bit. Unfortunately, you will not realize that you need a mutin until the frame is already stretched.
Sample photos:
FIGURE 01- Window Panel Strut: This is how you have to miter cut the alimunium frames. Two 90 degree elbows slide in the grooves to make a rigid corner.
FIGURE 02- Various Stages Of Completion: The middle two panels have been stretched with film and mounted with stops in place. The bottom window has no frame and no stops. The top left has just the stops. The top middle and top right have frames but the film has not been stretched and there are no stops. Notice that there is no condensation on the windows where the finished pannels are installed (middle and middle-left). If you look closely on the big middle window you can see that there is a little sag at the top of the panel. This is because I did not put in the cross brace (a.k.a mutin) that came with the kit. The film shrinks and is tight as a drum pulling in the sides. I will likely take this apart and put in the mutin later and then re-stretch the panel.
FIGURE 03- Joint: A miter saw is key for getting good cuts. I tried to use a hack saw but it was a pain and produced irregular cuts.
FIGURE 04- Wooden stops: Stops were bought at Home Depot for ~$0.59/linear foot. The stops here are dry fitted and have not yet been painted or glued down.
FIGURE 05- Recess Panel Mount: It took extra time to measure each dimension to 1/16". I measured these panels to be essentially flush with only 1/16th of space around the frame. The instructions say to leave 1/4 inch around but I felt that was too much. I suppose if the panels are completely flush with the window then any shifting over time will get transfered to the panel and this could lead to slack/wrinkles in the film. I will have to take my chances.
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1. AEP Frame temperature 59º F. Inside temperature measured at 66º F. |
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2. Original Aluminum Frame 52º F measured through the film. Note the recess mount. |
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3. Single pane glass 51º F no AEP. |
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4. Control frame measurement in another room 49º F. |
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5. Outside temperature 32º F. |
So, outside to window frame ∆ =19º F, window frame to AEP ∆ =8º F, and AEP to inside =7º F. This of course says nothing of air leaks but just conduction.