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I have wooden, single-pane (1/8" glass), double-hung windows on my house which have held up well considering they are nearly 70 years old. But, I don't want to put a lot of money into the house and I'm also good with my hands and have tools. I'm able to cut precise strips of wood like poplar and also paint them and have my own brad nailer etc.

I live in Central Texas where the temps can go up to 105deg F and down to 20deg F. Sometimes within 24 hours :)

My questions are:

  • Overall what is the feasibility of converting these single pane windows to double-pane windows? From a labor standpoint this is really not that hard. Nor expensive!
  • If I did this what would the optimal air gap be?
  • What type of "glass" should I use and would more exotic glasses really make a difference?
  • What percentage savings might I realize? (I guess measured in energy flow per hour given a specific temperature gradient)
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    Are you assuming that double pane windows are simply two pieces of glass next to each other? Because it's two pieces of glass that are sealed and have an inert gas between them. You can't make double paned windows on your own. – JPhi1618 Feb 28 '18 at 17:14
  • we don't have enough info to be precise: heat flow mechanics is a very complex subject. briefly: 1. doable. 2. more is better. 3. up to you, more expensive glass+filler gasses do increase R value. 4. impossible to say; EPA estimates are that 50-70% of an avg home's heat is lost through single-pane windows. – dandavis Feb 28 '18 at 17:17
  • since you live in a hot climate, you would do well to start with a tinting treatment on south-facing windows to reduce AC usage rather that increase heat retention with thicker windows. – dandavis Feb 28 '18 at 17:18
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    For the cost of the materials you'd buy to do this you can purchase vinyl replacement windows that will perform vastly better than what you'd build, and you may get lucky and have standard fitment. – isherwood Feb 28 '18 at 17:21
  • I agree with isherwood and jphil1618 you could add a piece of glass but it would probably end up with condensation between the glass panes. When I lived in Ohio we had a house with exterior storm windows that I replaced with double pane windows, that made a huge difference in our winter heating bill the next couple of years I did not notice AC two much because we only had a window unit. But I would consider remodel double pane, less work than making some custom trim and nailing and they will improve the value of your home if done correctly (it sounds like you have the skills to do it right) – Ed Beal Feb 28 '18 at 23:26
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I have done what you are looking to do with your windows, but with one big difference. It was an exterior door that was 1 3/4" thick. A considerable bit more room to add insulated glass to. Your glass cost will be considerable, and as others mention, they will need to be assembled by a glass company.

To recut the seat for the glass, I used my router set to the new depth and a flush bearing guide, so I could use the original edge that the windows set inside to act as the guide for the flush cutting router bit. After that I still had to cut out the radiused corners left by the router bit with a chisel so the glass would seat in all the way. After all that trouble there was just a marginal amount of room to set the beading after the glass was in place with the sealant. Quite the pain, IMO but it got done. There were only 9 pieces of glass to redo, it was a 9 lite door, glass only on the upper half.

If it were me, even if I had all the time in the world, for what you are looking to do, I would get window kits that replace the counterbalances of what ever the nature you have, whether it be springs, strings or sash cord with weights inside the jamb.

Several window producers make these kits to for standard sized windows and they slip right in... kinda. Remove the interior window stop and old jamb liners if you have them and the sash along with them or if you have sash weights they can be removed after the window sash are removed, there is an access to get them out. Insulate the cavity after you get the weights out.

To install can go a few different ways depending where you get them from, The ones I seen from Marvin, a few clips are installed to hold the jamb liners in, the liners are set in place and the sash tilted into the opening. My description is an over simplification, but I hope it gets the idea across.

One last note, I would do this only if you window jambs are in tip-top shape. Sills are typically the weak spot here.

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I've done this myself and I can relay my experiences. Doing this over the average of the two years I looked at about 10% difference in my heating bill. I replaced the windows with 1/4 glass with a 1/2 inch gap. My method was to use the original wood molding to rest the first replacement window on. I used glazing fasteners and then filled all gaps with silicon caulk. This was after insuring that the wooden window frame was is good shape and free from rot, defects, and loose joints. ANY air that pass through will be a problem for more reasons than just your bills.

After setting the first pane I surrounded that pane with 1/2 by 1/2 inch oak stained the same as the interior of the windows.I set this trim in a bed of wet silicone at the corner of the first pane of glass and brad nailed it into the window frame. I then set the second pane of glass using fasteners and silicone. It has worked really well except for one window where the joint failed and allowed moisture into the air space between the two. One moisture is in there you'll have to undo all the work and start over. Like wise only the interior window will be easily replaceable, if something breaks the exterior pane you'll likewise have to tear it all apart. For me its worth it.

I have a 118 year old home and I like my old double pane windows. Aluminum windows on this house would be a crime.

  • Paragraph breaks are your friend. Walls of text are not. – The Evil Greebo Aug 2 '18 at 13:08

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