AUSTIN, Texas — How to run your air conditioner directly impacts your electric bill.
A post on Reddit shows, “Man … I’ve been running tests and in this heat, unless I’m going to be gone for the whole day, it doesn’t make sense to turn off the AC. Just as much, if not more, power is used if I turn it off for four hours then back on when I come home later.”
THE QUESTION
“Could everyone turn their air conditioner off during the day to lower their power bill?”
THE SOURCES
THE ANSWER
No, depending on the outside temperature and since air conditioner performance and energy efficiency varies from home to home, some people may be able to save while others don’t. Even those who do save risk having other problems.
WHAT WE FOUND
The best option for an air conditioner to save money is by raising the thermostat a few degrees during the day and making other energy-conscious decisions.
“It also has to do with how efficient your air conditioner is. It has to do with how efficient and well sealed your house is, how well insulated it is. It is the way air conditioners work, if they move heat from inside of your house to outside. And if it's really hot outside and they don't have a good way, they don't have a good spot to put that heat. So it's much tougher for them to move that heat from inside to out,” said Hinson.
Pecan Street uses data, technology and research to help inform businesses and governments of ways to transition to a low-carbon energy system.
“When we do our engineering studies on this, we almost never use a single house on a single day because there's too many variables. There's temperature, sunshine and exact things that got used in the house that day. So we don't use a single house. We use hundreds of houses over the course of many days, months or years. We correct for temperature with cooling degree days and heating degree days, and all sorts of things to come up with these calculations. There's a lot of factors: the efficiency, the air conditioning unit, the efficiency of the house. It all depends,” Hinson said.
“Depending on how hot it is outside, it might take a very long time for the system to recover. Central air conditioners are not designed or should not be designed in residential applications to quickly recover the temperature in the house,” said Janowiak.
Janowiak said radiant temperature is the effective way to measure the temperature of a home.
“It potentially can take a long time to recover the temperature. But it's not just the temperature of the air that we're trying to recover. It's the walls, it's the furniture. It's everything in there. All of those surfaces will continue to give off heat,” Janowiak said.
Brandt said people could spend more energy trying to cool down a home after getting back home.
“Most people do not realize the total effect,” Brandt said.
He said an energy analysis computer program may help.
“It's situational. That's the word I want to use. So there is some merit to it, but it's not across the board in all instances,” Janowiak said.
Both Hinson and Janowiak said turning off the AC could also increase humidity in the home, which can lead to other problems like mold.
“When we see temperatures that we typically see for 80% of our summer, it's not going to run enough to get rid of the humidity. So you're trying to fix one problem, but you're creating a bigger problem on the other end. So there is a process. Air Conditioning Contractors of America has a series of design manuals, and we recommend that people follow those design things,” Janowiak said.
Janowiak suggests people invest in energy-saving improvements such as adding insulation and air sealing.
“People don't want to put money towards home improvements for things that you can't invite the neighbor over and show. All right, nobody's going to say, 'Come on out. Look, I got more insulation.' It just doesn't happen,” Janowiak said.
The Department of Energy offers a comprehensive guide on other ways to save money and energy at home.
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