Homemade double pane windows?

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Old 11-23-19, 01:13 AM
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Homemade double pane windows?

My house is not very well insulated. The vast majority of my electric bill is heating and cooling. One part of my house is the worst for this, there is a large space in the middle with a cathedral ceiling about 1.5 stories tall, and the triangular areas at the top of the wall on each side is a window.

It's a nice window, lets in lots of light, but its the only ones left in the house that are single pane. In the summer it is constantly covered in condensation on the outside. When it gets cold my power bill is ridiculous. The windows look homemade - just 4 triangles of glass that measure about 5'x4' on the straight sides, set into wood trim.

If I go through the trouble to add a second layer of glass is it really going to save me much money? It wouldn't be hard to put an extra sheet of glass on the inside under the trim, and seal it up well. Basically like a storm window installed on the interior.

Surely this would save something, but is it worth the trouble? Obviously, you can't get a window off the shelf anywhere that fits here. It's not a terribly hard job, but high in the air - would probably need scaffolding.
 
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Old 11-23-19, 03:42 AM
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If the glass is removable [like a storm window] it should work but if it's a permanent install you'll get condensation between the 2 panes with no way to clean it. Factory double glaze units are better sealed and have a gas between the panes.
 
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Old 11-23-19, 05:06 AM
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If I go through the trouble to add a second layer of glass is it really going to save me much money?
Short answer, it will help!

Ever see those indoor storm window film kits?

I had them in my first condo that had really cheap windows and they made a big improvement to the comfort of the home.

But as noted, a factor window, with inert gas and UV coatings is going to be a huge step above just a simple double pane window!
 
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Old 11-23-19, 07:13 AM
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Hi zeezz, easy to play with some numbers to see what your savings might be. Windows are a source of heat loss, but one window is probably not responsible for "When it gets cold my power bill is ridiculous."

Your two triangles together make a 5' x 4' rectangle, or 20 ft. The equation for yearly heat loss would be.
Q = U x A x HDD x 24 If we assume a single pane of glass is r=1 and I'll use zone 6 where I live your numbers are:
Q = 1 x 20 x 7000 x 24 which equals 3.36 million btu's. If we assume 100,000 btu's yield per unit of fuel (a gallon of oil in my case) we can divide that big number by 100,000. That gives us a yearly cost of 33.6 gallons, currently about $2.50 per gallon or $84 per year. Adding a second layer would increase the r-value to 2 or cut the u-value in half. Apply that half to the above equation and the yearly cost becomes $42, a savings of $42.

Obviously this is jut back of hand estimating but it illustrated 2 things.
1. Those triangle windows are probably not a big part of your heating costs.
2. And if the extra layer of glass doubles the r-value (a common estimate) the savings are modest.

If there is currently a lot of air leakage that can be addressed without a second layer.

If you want to unscramble these numbers I can do that. 

Corrections welcome.
Bud
 
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Old 11-23-19, 07:56 AM
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Cathedral ceilings look cool but are a pain in the butt to try and keep heat where it's needed.
The hot air rises and gets trapped at the peak.
Do you have ceiling fans to try and push the heated air back down where it's needed?
 
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Old 11-23-19, 07:03 PM
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Ever see those indoor storm window film kits?
That's kind of what I was thinking about. Does that really help if the window is not drafty at all? They don't open so they are sealed quite well.

Your two triangles together make a 5' x 4' rectangle, or 20 ft. The equation for yearly heat loss would be.
Q = U x A x HDD x 24 If we assume a single pane of glass is r=1 and I'll use zone 6 where I live your numbers are:
Q = 1 x 20 x 7000 x 24 which equals 3.36 million btu's. If we assume 100,000 btu's yield per unit of fuel (a gallon of oil in my case) we can divide that big number by 100,000. That gives us a yearly cost of 33.6 gallons, currently about $2.50 per gallon or $84 per year. Adding a second layer would increase the r-value to 2 or cut the u-value in half. Apply that half to the above equation and the yearly cost becomes $42, a savings of $42.
Great information! If I just round the numbers a little bit...there are a total of 4 windows, each triangle is cut in half to make 2 triangles with a center support, so roughly 40sq ft. So if I lost 6 million BTU/year, my heat pump is 60,000 BTU so it runs 100 hours/year for the windows. That's about $90. Much less than I would have thought!

If I did something to frost the glass would that help reduce solar gain in the summer? They're up so high I can't see anything through the glass anyway. This would also hide the constant condensation. I'm in NC by a lake, so it's not uncommon to see 80-90% humidity in the summer...
 
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Old 11-23-19, 07:26 PM
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There are film coverings that can reduce the solar gain, but may work against you in winter.

Years ago it would have been common to have a storm window custom made so you could use as desired. You might talk to a window company they oftan have very experienced employees and may have some ideas.

I think the benefits of a second layer would go beyond just saving money, that would be the bonus. Eliminating or reducing the condensation and perhaps improving the comfort are both important.

One drawback for having a heat pump is you use less energy so save less, but an acceptable issue. I have a cape and being a retired energy auditor and former contractor I have gone far beyond that payback threshold because I'm doing the work by myself. But it feels good and provides this old guy some personal satisfaction.

Bud
 
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