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Question DetailsAsked on 9/22/2014

Is it better to run the air conditioner or open the windows?

We've had a very pleasant month of July here in Indianapolis, with temperatures regularly maxing out around 75-80 degrees, which is abnormal for this time of the year. While there's nothing better than opening up the windows to let the breeze in on a nice day, I have pretty severe allergy problems that limit the amount of time we want to have our windows open, so the A/C is usually on in our home and set to around 72.

I'm wondering where other people draw the line when it comes to running their air conditioner in the summer? Is it a last resort? Always on? Share your thoughts!

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1 Answer


My experience is most people turn it on when the heating season is over and let it run on its own - possibly with a temperature change at night using an automatic setback thermostat. Obviously, from an energy efficiency standpoint, if you can open the windows and not run a furnace or A/C, especially if you time it to trap warm or cold air when you want (open in cooler evening to cool house but close before it gets colder outside than your desired nighttime temp, and in morning to trap cool outside air in house before house starts heating up from the sun) then you will save energy. You would not believe all the money I save by never running an A/C in my home - course, I don't have one to run, either), so I saved all that capital expense and maintenance cost too !

With your allergy situation, IF you have central air (where the furnace fan provides the airflow for the A/C also, through the same ducts) then you probably don't want to leave the windows open and let all those allergens in - not only to contaminate the air, but to settle on furniture and carpeting and such and get continually kicked up into the air. However, with central air you have the option of running just the fan (may require a change in thermostats and not easily done with all units, but most newer ones it is not hard to set up) without runnign the A/C - that will recirculate the air in the house and filter it, without the energy consumed by the A/C unit possibly only cooling the air a few degrees. Some thermostats have a manual "fan" setting, some have a totally separate programmable timer function to run a fan periodically when the switch on the thermostat is set to fan.

Been a long time since I did this - but as I recall was about $350 for an HVAC tech to do it with a digital control central air and two new thermostats (2 zones), though if your thermostats are newer you may be able to use them. Who knows - read your instructions for central air system and thermostats - may already be set up to run and all you have to do is program the thermostat for the conditions when you want to do it. Toughest (and costliest) case is if you have to also run new wiring to the thermostats and they arenot right above the furnace. And of course, if you do not have central air, your A/C system may or may not be designed to run in fan-only mode, either in ducted or mini-split system- some will, some won't.

Also is done at times to remove cold or hot spots that form in the house, or to remove odors in houses with diaper age kids or a lot of open-pan cooking, by circulating the air even if the temperature is not such that the furnace or A/C has to come on.

Answered 5 years ago by LCD

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