Ask Umbra: Is it bad to leave a window open when the heat is on?

Q. Dear Umbra,

When I was in college, I had a friend who thought she was eco-conscious, but she used to crank the heat and then leave the windows open for “fresh air.” Years later, I dated a woman who lived in a building where the heaters were stuck on high and the windows were all open. Fast-forward to now: My wife likes to have the radiators on with the windows open … for the ventilation. While this seems obviously a waste of money and bad for the environment, I don’t have the facts to show her why it is so bad. Can you help?

Ann
Seattle

Mmmm, fresh air. Photo: Lori L. StalteriA. Dearest Ann,

I wonder what Window Deity you angered in a previous life, that you should be so shadowed by friends and partners who live in this extravagant way.

You’re right that cranking the heat and opening the windows makes very little sense. I can say with 100 percent certainty that your wife is wasting energy and money.

The basic idea of a heating system is to put warm air into a space until that space reaches a certain temperature, recognized and governed by the (programmable, we hope) thermostat. If the warm air is wafting out into the cold, as warm air is wont to do, the system will keep cranking away, merrily burning oil or gas or what-have-you. I checked with Max Sherman at the Lawrence Berkeley National Laboratory, who confirms that this habit will certainly increase your heating costs, in some cases even doubling them. One of the key things we should all do to make our dwellings more energy-efficient is seal up leaks; open a window or two, and all that work is for naught.

You say ventilation is the primary concern. Sherman also happens to be an indoor-air-quality expert, and he says windows are not a good choice for ventilation, except during very mild weather. He and other experts recommend instead a simple system such as an exhaust fan, or something more convoluted like a heat-recovery ventilator (HRV). These HRVs are nifty whole-house systems that ventilate your space and also capture and reuse the energy from your heated air. While they can cost a lot to purchase and install — $2,000 or $3,000 — they cut down on heating costs enough to pay for themselves in a few years, so they can be a good option for homeowners.

For others, especially renters who don’t have thermostats in their apartments, opening a window can feel like the only alternative to roasting. But there are a few other ways to beat the heat:

1. Talk to your landlord. Explain your situation — preferably with some other sweltering residents in tow — and be sure to mention that lowering the heat or giving the system a much-needed tune-up could save the landlord money. In general, each degree lower on a thermostat can save 3 percent on energy use. Sounds eensy, but it adds up.
2. Be wise about appliances. Small, unused appliances that are plugged in generate heat. They also happen to waste 5 to 10 percent of your home energy. Unplug them! And if you’re lucky enough to have heat-generating biggies like a dishwasher or washing machine, use them in the early morning or late at night.
3. Use CFLs. Besides being energy efficient, they produce 70 percent less heat than incandescent bulbs.
4. Befriend some houseplants. They won’t cool you down, but our leafy friends are good at improving indoor air quality. Get some that like tropical temperatures, if you must. And know you’re breathing cleaner air.
5. Wear a bikini. If nothing else, Ann, this last tip could make your window arguments a little more entertaining.

One final suggestion: This handy tool illustrates your home energy costs, after you tell it lots of things, and might also help make your case. Good luck.

Itsy-bitsily,

Umbra