Kim asked a great question which I’m sure a lot of us have wondered about but been too lazy to really investigate. (That includes me. I made Otto look it up.)
Hi pretty girl,
In the midst of all of this insane heat, we have had quite a discussion here at the water cooler. Is it really cheaper to turn your A/C down during the day and have a programmable thermostat bring it back to temperature for your return? Please end this obnoxious debate. Thanks!
As someone who doesn’t have central AC, I guess I’d not thought about this too much. I have window units which I use as little as possible, and so if I’m not home, they’re off. But if you have central AC, what’s going to be the best bang for your buck?
After some searching, Otto found this great FAQ list about air conditioning. I recommend reading the whole thing just because it’s full of interesting and useful information about energy consumption and efficiency and all that good stuff.
I believe the information you need to end the water cooler debate, Kim, is in this bit:
Will I save energy by turning off my air conditioner when I leave home, or am I better off just letting it run?
If gone for four hours or more, more energy will be saved by turning off the air conditioner or turning up the thermostat.
During the day, keep windows shut and close curtains or blinds on any windows that will be exposed to sunlight.
The thermal mass of the house will probably keep the indoor temperature well below the outdoor temperature, and the house should cool quickly when the air conditioner is restarted. Use a programmable thermostat or timer to turn on the air conditioner 30 to 45 minutes before the expected arrival home. If the home is still warm upon arrival, turn on a fan to create air movement.
Moving air can make the air feel about four degrees cooler than it really is.
We also found that Mr. Electricity has discussed air conditioning as well (although, seriously, avert your eyes from his photo, because I was certain he was Weird Al Yankovic at first glance), adding this explanation:
It’s a myth that leaving the AC on while you’re away at work uses less energy than turning it on when you get home. Think about it: Heat constantly penetrates your home, and that’s what your AC removes. If you turn on the AC when you get home, then your AC has to remove the accumulated heat only once. If you leave it on during the day, your AC must repeatedly remove heat that enters your home.
You might think that there’s no difference, because your house should absorb the same amount of heat either way. Not true. With the AC off, at some point your house will be so hot that it can’t absorb any more heat. But with the AC on, your house will always be cool enough to absorb more heat — and you’ll be paying to remove that heat, over and over again.
Bottom line? Turn it off. Set it to cool the house back down before you get home, and enjoy the savings. Use your extra money to shop for deals here at Want Not! (Wow. Sorry about that. It must be a little too warm in here….)