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I have 11 square 31"x31" double-glazed windows (likely not low-e glass) that are aluminum framed without a thermal break, so the interior frame becomes almost too hot to touch in the summer and gets wet from condensation in the winter when it is cold enough.

These windows compose about 30% of my house's total window area. They are recessed into the wall by about 5" or so. Replacement of the entire assembly is complicated by the metal-sided nature of the house and quotes have been $800-1000 per window (if they will even mess with a metal-sided house).

I feel the windows are a large source of inefficiency in both the summer and winter, and the interior window does feel colder or warmer (depending on season) than ambient interior most of the time (aside from the heat transfer through the frame issue).

Rather than replace, I'm considering DIYing secondary glazing to the interior of the windows. I would cover the existing interior exposed aluminum frame with clean looking weather stripping or foam and seal a new piece of (likely wood-framed) glass to the interior with caulk. I'd probably use plain glass, but would rather use low-e glass. I have not found a supplier for single-paned low-e glass, but I've found someone that would sell me a custom-sized double-paned low-e module for around $100 each.

Questions:

  1. Is this worth the effort? Total cost for the addition of a low-e double-paned module behind each window would be somewhere around $1500. This would leave me with basically a quad-glazed window, which I'm sure is overkill, but one layer (inside of the third pane of glass) will be low-e and the additional air-gap may better insulate against heat transfer through the interior frame. Cost would probably be half that or less for regular single-paned glass.
  2. Are there problems I'm not considering? I'm specifically worried about condensation between the original window and the secondary glazing, but I'm not sure how much of a problem this will be as the gap will be pretty much air-tight.

Window

Frame close-up

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  • Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer.
    – Community Bot
    Nov 3 '21 at 15:34
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    "Is it worth it?" is an opinion based question and those are specifically off-topic. To me, $1500 for all windows vs $1600-2000 for two windows is definitely worth a shot, however, you're still questioning it. i.e. difference of opinion and there is no "right" answer. Either that or I'm reading it wrong and it's $1500/window so the answer is "no way!", but you're still considering it. Still a difference of opinion with no "right" answer.
    – FreeMan
    Nov 3 '21 at 16:03
  • I'd just replace the windows. You wont see a return on the cost unless you live there forever but think of the comfort you'll have from it. Nov 3 '21 at 17:41
  • Welcome, Arif. Please take the tour so you know how to use this site.
    – isherwood
    Nov 3 '21 at 18:29
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This likely won't work as you hope. Home-built glazing is highly prone to leaks, which means you'll have moisture, dust, and eventually mold in your windows. You'll put all that effort and expense into the project and be unhappy in a year or two. It was ok back when everything was single-pane, but not for multi-pane situations.

I'd either bite the bullet and update your windows properly (which should add value to your home, where hodge-podge won't), or order full replacement custom glazing for the existing windows (which won't help with the aluminum's conduction, but you could maybe insulate that with some covering material).

We're into the realm of opinion here, but a refinance at low interest to cover the cost of proper replacement is probably a good investment on this rapidly roasting planet, should you not have the capital to lay out. Buyers want efficiency for both the economy and ecology of it.

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I’ve been to a seminar where the Department of Energy showed that most of the heat loss and heat gain was through the roof, not walls. They can do calculations showing how most energy (and cost) you’d save if you added 6” of attic insulation or the same amount (cost) on replacing windows. The attic insulation has a payback of 2-3 years, while window replacement took 24 years or more.

You don’t seem to be complaining about the indoor temperatures, but my point is that replacing or repairing windows is very expensive and will take a long payback period to recover your cost.

Your complaint seems to be about the frames. The frames do not contribute much to the heat loss or heat gain. Rather, it’s a comfort issue when you touch them or when they develop condensation.

I’d spend my money on isolating the frames from the exterior environment. You could add storm windows on the exterior of the windows at a reasonable cost.

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  • The attic is getting insulated (radiant barrier + blown insulation) in a few weeks, and I think that's going to make a sizable difference given that it gets up to 40 degrees above ambient in there and bakes the hvac system. The indoor temps can be a problem on the second floor, where the 4 ton AC may have to run constantly in peak summer to maintain temps. In direct sun, these frames get to be extremely hot - like hot enough that I can't keep my finger on them for very long. It just seems that a lot of heat is getting translated around the window. It seems very atypical.
    – Arif
    Nov 3 '21 at 21:18
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If you want a low-budget fix you could always add some low-e window tint to the existing glass. This will stop much of the heat that comes in with sunlight.

For the window frames, they would need some insulation, and one idea would be something like a Plasti-Dip spray. Its not much, but the layer of vinyl would help some of the conductivity issues and could control condensation a bit in the winter.

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A friend had a big double-glazed unit that failed which then developed condensation inside.

We drilled 2 small holes (about 1/8" or approx 3mm) in diagonal corners then made a small pump to draw air out through one of the holes. Dried air through a filter box filled with those dessicants that come with new electrical things was connected to the other hole.

Within a week the unit was condensation free - plugged the holes (used blutack as it comes off easily) and kept the bits - about every 2 or 3 years…

Given you will be relying on the wall surround for a seal you might want to plan ahead.

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  • Ok, great, I expected at least a 1/4" hole. Could probably even get a bottle of nitrogen to ensure you fill it (mostly) with clean dry air. Thanks for the tips!
    – JPhi1618
    Nov 3 '21 at 19:25

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