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Alice writes,"What better saves energy: insulation or new windows?
Our brownstone is very drafty. We can only afford to do one energy saving application. Should we open our floors and put insulation or get new windows?
Thanks!"
As a former student of Gail Brager, UC Berkeley professor and one of the world's leading researchers in building performance, we can answer this question with confidence.
Do the windows.
Here's the funny thing: overall, you would increase the insulation value of your house the most by adding insulation. But air takes a lot of energy to heat up or cool down, so when it leaks out through drafty windows, you have to use more energy to heat more air.
As a side benefit, if you replace the windows with new ones that are both double-glazed and that have a Lo-E coating, you'll increase the thermal comfort in your house. That means the glass surface of the windows will not get as cold on the inside, so you will be able to sit close to them in the winter without feeling a chill.
In fact, air infiltration -- the building science word for drafts -- results in 33%-50% of heat loss in the average house; if yours feels drafty, it could be even higher. (PDF with more than you probably want to know about this here.) So, our advice is to go for the windows first: either replace them outright or carefully weatherstrip them and add storm windows, which might be a better choice if they are historic or in good shape otherwise. Then bank your monthly energy savings next winter and use it to insulate the house from the top down: attic, side walls, then basement.
Image from PK Energy Controls, a company that will take pictures of heat loss using an infrared camera.
This sounds like a silly question, but does the same principle apply in a hot climate with loss of cool indoor air?
view Deidre88's profile
This got me thinking: how much of an impact do shades and or curtains make in prohibiting heat loss? While probably not in the same league as double-hung windows they surely do help?
view Maryja's profile
Maryja,
That's a tough one to answer. Let me do some digging for a future post!
-jonathanb
view jonathanb - co-editor, AT/re-nest's profile
For a purely anecdotal answer to Maryja's question... it's not a coincidence that Victorian window fashions in colder climates involved heavy velvet drapes that puddled on the floor and had a lot of hoohah for a valance. All that fabric helped the room retain heat during the winter. We could feel the difference when we closed our 10' velvet IKEA drapes.
view wende in phoenix's profile
Thanks for answering the question. The windows are in bad shape so new ones are in order. Now we just need to find a reliable installer.
As to drapes, my sister in law lives in a cold rural area and using insulated drapes in the winter and it helps a lot.
view Alice42's profile
Alice--I'm in dire need of new windows as well. What brands of windows are you considering?
view dollhouse's profile
In response to Deidre, from what I know in my course study, the same is for the referce. If you have alot of hot air making it into your home, the harder your AC has to work. I'd say your first bet is to have a better seal for air. Then after that, worry more about heating load from the sun, white shades work wonders in the summer.
view shadowswimming's profile
shadowswimmings response to Deidre also kind of relates to my question about curtains retaining heat, except in reverse.
Growing up in New England we often kept the shades/curtain drawn during the day to preserve the cool air that circulated at night when we would open windows. I recall it working and do the same out here in the PNW when it occasionally gets hot but is it based in fact or just an old wives tale?
view Maryja's profile
That's a brilliant advice, I was a little bit doubtful about that but your arguments made me decide for windows. I would also love to know more about double glazing cost so I can start making plans.
view albert31's profile