Our guest blogger today is Capstone Mechanical of Waco, Texas. Although this article was written with air conditioning in mind, the same truths would apply to heating as well.
On a 100 degree day, does setting back your thermostat to 80 F when you leave the house really save energy? Many a wise service technician has told a homeowner that it doesn’t. This is usually under the premise that the unit is just going to have to work harder to get the temperature back to 75 F when you get home. Nobody wants to make their air conditioner work harder. That sounds expensive. I’ve heard techs say you should treat your house like your refrigerator. You don’t change the temperature on the fridge everyday so why would you do it on your house?
The reality is that the amount of air conditioning a house needs is typically directly proportional to the difference in temperature between the outside and inside of the house. For instance, if it is 100 F outside and you raise the indoor temperature set point from 75 F to 80 F then the temperature difference has been decreased by 20%. This will equate to roughly a 20% difference in the amount of air conditioning that your house will need and a decrease of the energy needed to cool the home.
But what happens when the set point is changed back to 75F? Here’s where a lot of the misunderstanding is. The air conditioning system doesn’t work “harder” in order to cool it back down to 75 F but it will run longer. For a well maintained system this is not a problem but if the unit is very old or in poor shape, the longer run time could expose a problem. This is another good reason to make sure your unit is checked by a professional before every cooling (and heating) season.
So did you save energy?
Yes, for whatever the amount of time you were able to leave the house at 80 F instead of 75 F there was a 20% reduction of energy (assuming the 100 F day). The longer you can leave it at 80 F the more total energy you’ll save.
But what about the energy it took to cool the house back down from 80 F to 75 F, didn’t that erase the energy savings? No, that energy was a fraction of what it would have taken to keep the house at 75 F while no one was home.
One thing you do need to take into account is the time it takes the air conditioning system to recover back down to 75 F. There are a lot of variables that go into this, but typically it will take from 30 minutes to an hour. This is why you need a programmable thermostat so this can all be done automatically before you come home.
So, this myth is totally busted.
Don’t be afraid to set the temperature back in your house. It could save you hundreds of dollars a year and that will more than pay for that programmable thermostat.
Thank you Capstone Mechanical for the great information! If you would like to read more, visit http://capstonemechanical.wordpress.com/. If you would like more information about programmable thermostats, the experts at P.K. Wadsworth would be happy to help you if you’re in the Cleveland area. For homeowners in the Waco, Texas area, contact http://www.capstonemechanical.com/ for more information.