House in Progress Diary

: Diary | Ideas | Reviews | Shop | About Us

Wood Windows and Energy Efficiency: Thermal Loss

Part One here and Part Two here. You won't want to miss them. They're cliffhangers, I promise you.

Now, let's talk about thermal loss. Although it is rather straightforward to do something about infiltration, thermal loss is where wood windows do fall short. (Even though they look great doing it.

Why though? Why do old wood windows have thermal loss? (Beware...this is where I get all geeky on you. Engineering and physics purists, yes, I know I've oversimplified this. Please correct me in the comments.)

Remember sixth grade science class when you studied thermal conduction? No? Too busy scoping out Brian Martinfinkel, eh? Passing notes? I knew it. Okay. How I can explain this...?

I know! Let's go shopping at Williams-Sonoma (hurray!) instead of working on these old windows. We're going to want to find the pots and pans which are the best at heating our food on the stove. Hmmm. Would we choose a steel pan? A ceramic pot? Glass bowls? Or a wood skillet?

Oh, right. They don't make wood skillets. Do you know why? Because wood doesn't conduct heat very well. However, metal, ceramic and glass all conduct heat. (Remember Pyrex? And, there is a tempered glass that can be heat resistant, but I'm talking about regular window glass here.)

You might want a radiator made of metal or glass, but not wood.

Conduction in heating or cooking = good!

Conduction in your window glass = bad. You don't want the heat to go through the glass and leave your house! You want the heat to stay inside where YOU are. So, you want to figure out a way to keep more heat on your side of the glass.

Now, let's walk away from the cookware and, hey! Williams-Sonoma is selling this charming GLASS drinkware from Bodum. But, but, wait a minute! You can drink ESPRESSO out of these glasses? We just learned that glass conducts heat so how could you drink piping hot espresso out of these glasses without burning your hand?

Look closely. These glasses are actually two glasses, one inside of the other, with air in between. So, when you hold the outer glass, the pocket of air is protecting you from the heat of the inner glass.*

A double-glazed window works this way as well. Air between two panes of glass keeps more heat on the inside of your house and keeps more cold out. The air in between the the panes acts like a moat. Double-glazed or even triple-glazed panes don't completely halt thermal loss, but they slow it down.

So, yes, right. If you compare a single-glazed pane with a double-glazed pane, the double-glazed pane is going to win. But is that the WHOLE story? No, it isn't.

Single-glazed wood windows are meant to be used with a storm window. They were built for that. Many of these studies only compare a wood window without a storm against a double-glazed window. And THAT isn't a fair comparison. Because a tuned-up wood window paired with a quality storm window can approach the energy efficiency of a double-glazed window. And sometimes it can achieve this efficiency for less money.

If you are interested in the study of how old wood windows performed in cold climates, you can check out this report from the National Center for Preservation Technology and Training. If you want the summary, just click down to page 81 in that report for a recap of how wood windows performed when different variables were put into play.

The gist of it is this...you can possibly save money by tuning up your old wood windows and pairing them with energy efficient storm windows. Even if you pay for lead abatement of the sashes.

Here were the pro's and con's that I came up with:

CONS

Wood windows aren't maintenance free. I would have to learn to care for them.

Our current sashes require lead abatement.

There are some panes of glass that need to be reglazed.

I would have to do the weatherstripping and insulation of the wood windows.

PRO'S

I can do the deinstallation, reglazing, weatherstripping, painting and reinstallation myself without having to deal with an outside contractor or supplier working in my house.

It's relatively cheap to restore the windows in terms of cash outlay, even with the lead abatement. An average cost of $100 - $140 per window.

Almost all of our sashes are in good shape, and any repairs are minimal (can be completed using clamps, wood glue and wood filler). Only a few storm windows would have to be replaced.

I could learn to retrofit the wood storm windows with swappable storms and screens, thus eliminating the inconvenience of taking down and storing the storms each spring.

The wood windows look a heck of a lot nicer than any replacement windows that we could afford.

I would be saving old growth wood that otherwise would have ended up in a landfill.

Our windows were already using chains instead of rope, which I like the look and performance of.

Once the windows are stripped down and tuned up, they will open and close pretty easily.

See? I told you. I'm picky with details and short on cash. Given my criteria, wood windows win for me.

"But what about vinyl replacements?" You say. "Did you consider vinyl? Because those are relatively inexpensive!"

Yes, yes I did. We can talk about those next.

Posted by jeanne on August 5, 2007 at 3:42 PM (5)

Looking for More?

	Search for more on 'wood_windows' on this site.
	Search for 'wood_windows' on on other houseblogs like this one.
	Search for 'wood_windows' on Google.
	Search for 'wood_windows' on Amazon.com.