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Replacing single-pane windows - keep storm windows?

Replacing single-pane windows - keep storm windows?

Old 01-12-12, 08:33 AM
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Question Replacing single-pane windows - keep storm windows?

I currently have single-pane windows plus storm windows. Eventually I need to replace the single-pane windows with double-pane for energy savings and comfort. When I do that, should I keep the storm windows or just get rid of them? I'm partially thinking I should just keep them, since they're already in place and it affords an extra layer of protection/insulation. On the other hand, they're inconvenient for cleaning, and I'm not sure how much insulation they really provide.

Old 01-12-12, 08:53 AM
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Your single pane windows are essentially double pane because of the two layers. Replacing windows to improve your energy efficiency, IMO, should be reserved for last and if possible, combined with other improvements. The majority of people who go for the windows first are disappointed in the improvements, unless they are like my wife and just wanted new windows in the first place.

New windows come in two forms, "new construction" and "replacement" style. New construction comes with a completely new frame, but requires that you mess with the outside and inside trim. Replacement windows are ordered to fit inside your existing frames and trim, thus a bit smaller than what you have and although easier, it fails to improve the installation (their perimeter) which is often where a lot of the air leakage is coming from.

Some basic numbers. Windows are approximately 20% of your total heat loss. Switch to new double pane windows without the storms and maybe a 25% reduction in what was going out that way. That's 25% of 20% for a net savings of 5% in total heat loss, with a simple payback often in the range of 20 years. Leave the old storms and a little bit better. Window sales people can often come up with much better numbers, I wonder why?

I was replacing my siding, so the opportunity to replace the windows made sense and it made the wife happy. They look nice, they tilt for cleaning, and they were installed with foam all around so no extra leakage. Net result is they will save money and I don't plan on moving so long term is just fine for me.

Old 01-12-12, 09:11 AM
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I've installed windows for over 20 yrs, and the first thing I will say is that I am not convinced that a double paned window will in ALL CASES out perform a single paned window that has a single paned storm window. (which essentially is an unsealed double pane window, as Bud mentioned) I have seen too many instances where people NEVER had any issues with fogging or condensation, but after they replaced their windows they had a little- which was a surprise because prior to replacing their windows, they had none. This isn't the case in EVERY house I've worked in, but it was true in some. What this tells me is that in some cases- perhaps especially in humid houses- storm windows can be a real benefit to have.

If you get new construction windows, you would not be able to reuse your existing storm windows. But if you get replacement windows that go into your existing jambs, as Bud mentioned, IMO the storm window "wouldn't hurt" as far as giving you a warmer window is concerned. Triple glass is always better than double or single glass. The storm window will provide a buffer for your main window, which will raise the interior glass temperature of your main window, making it feel a little warmer. It can also help with air infiltration on windy days since it will slow the air speed before it gets to your main window. There are potential problems though.

1). you can get fogging between the new window and the storm window. Someone recently was complaining about that in another thread here. Moisture can get trapped between the storm and the window- especially if you caulk your storm windows on (which I never recommend doing).

2). your storm windows will be impossible to remove from the inside. Depending on what type of new window you have, they may also be impossible or at least difficult to clean. In that case, you would have to unscrew the storm window to clean it.

3). if the windows are in direct sunlight, there can be excessive heat buildup in the summer months, which "might" shorten the life of your IGU (insulating glass units- the sealed double paned glass part of your window). Some mfg's may not warranty their double-paned windows if storm windows are installed over them, you would have to ask them specifically for that warranty information.

It's very interesting to take one of those digital laser thermometers and take glass readings on a cold day. On a double pane window, the warmest part of the glass will always be "center of glass". This is because on an IGU, the perimeter, or edge is coldest. It's thermally conductive, meaning most of your heat loss occurs on the edge of the IGU as heat radiates from one side of the glass to the other via the spacer material that touches both pieces of glass.

This is why they have developed "warm edge technology" (the word warm being relative, of course) using less conductive materials so that heat loss is minimized. So when you get your new windows, try and ensure that the IGU's will use some type of warm edge spacer material. Swiggle, Intercept, Super Spacer, are some name brands you can look for. They are all superior to plain old aluminum, steel or other metallic spacers.

So after your new windows are installed, it would be very easy for you to actually take some "center of glass" temperature readings with and without a storm window installed. (if you can buy or borrow a laser thermometer... a cheap one is about $20 online) Just keep in mind some of the drawbacks mentioned above.
Old 01-13-12, 05:36 AM
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Besides all the good and useful information above, I have a question and a possible problem. You didn't mention the type (double hung, slider, etc.) of window. The problem you might find is that you may not be able to remove the glass inserts from the storm windows for cleaning or repairing a broken glass since the replacement window shrinkes the opening. Leaving the storm windows will ruin the look of new windows.

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