Running your Air Conditioner when its 100+ Degrees Outside

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Running your Air Conditioner when its 100+ Degrees Outside

Here in Houston we just set a record for a straight 15 days in a row with daytime temperatures reaching or exceeding 100 degrees Fahrenheit. Yes it’s hot, and air conditioners are taxed to their performance limits to try to keep up with cool air demands. Here’s some things you need to know about running your AC unit in these kinds of conditions.

Should Your AC Unit be Bigger? No!

Central air conditioning systems are designed to suite the size of your home and the amount of air it needs to cool or heat. The size of the specific AC unit, the condenser, is chosen to be efficient for 98% of the typical high temperatures in your area (climate). So for that 2% extreme, like we are having this summer, your AC system may actually be undersized. But this is by design. Otherwise, if you went with a larger system that had no troubles pumping the volumes of cool air needed during these extremely hot days, your system would be quite inefficient 98% of the time. And that’s really almost all the time – not a good thing.

The larger system costs more to install and it consumes more energy to run, all costing you more money. Because it pumps more air volume it cools the house much faster. You might think this was a good thing but instead it means the system is running through off and on cycles at a much higher rate. The shorter cooling cycles means it is not quite running long enough to be pulling humidity out of your home. Removing humidity is part of how an air conditioner works. The condensing coil condenses water out of the air and the heat exchange process during that activity is what creates the cooler air. Warmer air and moisture is then exited from your home. Dryer air, even when warmer, is more comfortable for the human body as it allows our internal air conditioning, evaporation of sweat, to be more efficient. Not removing sufficient humidity from your home could also lead to mold problems.

These are some of the reasons an over-sized AC system is just an all around bad idea. But you can still make the system you have work for you in these 100+ degree conditions.

Juicing More Efficiency out of Your AC System

To make it easier for your AC system to reliably pump out cool air when it’s over 100 degrees outside you need to give it some help. We previously wrote a huge list of tips for energy savings in relation to ac usage. Apply as many of those as you can to help your cooling system cope in this heat.

In a nutshell it comes down to reducing heat gains in the home. Some of the basics are;

  • turn the thermostat up a couple degrees and be happy with 76 to 78 degree temperatures indoors
  • close off unused rooms – close doors and vents – don’t cool what you don’t use
  • shade your windows on the sunny side of the house
  • cook outdoors – enjoy the summer BBQ
  • don’t use dry cycle on dishwasher – leave door open and let them air dry
  • don’t run clothes dryer during the heat of the day
  • read more tips here

Anything you can do to keep the house cooler, even a little bit, means the AC does not need to be running as long for each cooling cycle.

AC Maintenance is KEY!

Your central air system should be getting a maintenance check up at least once a year. Ideally the AC unit should be checked before peak demand in the summer heat, to ensure it’s running at it best when you need it most. It will be running long and hard through these multiple 100+ degrees days and may even need a check up later on after all that heavy use.

If you’ve not had your system serviced yet this year, call your ac contractor (in Houston and area, that’s us) and get it done. But you might need to wait a while, we get very very busy in times like this (does everyone wait till the last minute? Seems they do).

At the very least, go check your filters. Fresh clean filters allow more cool air to flow unobstructed. If the filters are only a little bit dirty, put fresh ones in now for this extreme heat period. You can still reuse those slightly dirty filters if you wish later once the summer begins to die down.

By |2018-11-30T15:19:54+00:00August 16th, 2011||15 Comments

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  1. Lois Camper 06/13/2016 at 4:30 pm - Reply

    Its calling for 119 plus weather here in Arizona for the next couple of weeks. I have a 16 seer ac unit. What would be the ideal temperature to set it at and not make the electric company rich.

  2. Lois Camper 06/13/2016 at 4:31 pm - Reply

    What would be the ideal temperature to set my thermostat in 119 degree weather without making the electric company rich?

  3. Timmy Clark 06/21/2016 at 9:56 am - Reply

    There is no proof the larger units dont work as well or cost more. Unless over sized greatly it is not proven to cost or not dry the house.

  4. Mike Smith 07/11/2016 at 6:33 pm - Reply

    Lois, maybe 85ºF when It’s that hot??

    • JLN 07/18/2016 at 9:10 am - Reply

      Set thermostat to 85 degrees when it’s 120 degrees outside? What…are you nuts? Here in Oklahoma, where it very humid, it’s getting into the 100s with 90 percent humidity! At 105 degrees with 90 per cent humidity, setting the thermostat to 76 degrees simply does not cool down my two-story home. I have two units – one up, one down. It’s just miserable here in my home unless you sit directly in front of a fan with a wet cloth around your neck, take a shower every few hours, or in-and-out soaks in a pool (which I do not have)! Thermostat at 72 degrees is working much better for my family!

  5. tracie 07/18/2016 at 6:40 pm - Reply

    It’s been averaging 100-109 here in SoCal, I keep my ac at 78 and I’m in a tiny 1 bedroom . My bill has been 60. Well last month it was 154 now it’s 235 what can I do to help save money. We are on minimum wage and can’t afford this

    • RM 08/02/2016 at 8:52 pm - Reply

      In SoCal, to lower costs of electric bill, you have to figure out the rate plan you are on. Is it tiered? If so, the more you use, the higher the rate.

      So, the trick is to cut all nonessential electric items. Toaster (use gas stove if you have one), cfl light bulbs (use LED, can get at Home Depot for $2 each), lower fridge temp, cut tv.

      Now, for the folks who are on minimum wage, call the electric company, and tell them you are a family that makes less than enough.

      They will give you a crazy discount, since the state has a program for this, and the electric company pushes this plan. No hassles. I’d do this first.

  6. gail mulcahy 08/07/2016 at 2:17 pm - Reply

    what are bad affects to a condo if you don’t run A/C in 111 degree weather all summer? because it is a vacation property aND not used in summer mos thru October.

  7. Houtex77 08/14/2016 at 2:27 pm - Reply

    When I leave for work, I turn it up to 80. When I come home, I turn it down to 76. It takes a long time for it to cool down. Should I not turn it up that high when I leave or work? Thanks.

    • Dave Mills 08/19/2016 at 4:47 am - Reply

      Get someone to put a Thermostat with a timer in it that lets you program your Temperature setting for multiple times of day. Then set it to go to 80 degrees 1/2 hour before you leave for work and back to 76 1 hour before you come home. Viola problem solved.

      I hope this helps!

      • Houtex77 08/19/2016 at 5:23 am - Reply

        Thanks Dave, yes it helps. I never use my timer. I’ll learn.

  8. Gina Marie 06/19/2017 at 11:02 am - Reply

    I recently got a new AC unit my old one was from 1992. This one does not seem to cool as well especially in 98 degree+ weather with humidity. I put a dehumidifier in the basement and it helped a bit. But if I set the house up to 80 degrees when I leave and when I return from work back to 78 degrees it can take almost 2 hours of continuous running to cool to that temp. Is that normal. In addition when it is just cycling normally between 1 pm – 7pm it seems to run for about 45-1hour to keep 78 degrees then it is off for about 8 minutes then back to about 45 min of running. I started to use a portable AC in the main room with the thermostat just to help which has made the cycling about 13-15 min run 8 min off. The house is well insulated as it has been foamed. My question is this normal operation for an AC unit in 96-100 degree weather with humidity? The company says yes but it seems odd to me. Under normal 85-93 degree weather the unit seems to run 11-13 min off for 8 min during heat of the day.

    Thank you

  9. Dean Van Landuyt 07/31/2017 at 8:51 pm - Reply

    Thank you. This is logical, helpful, and well-written.

  10. Rhianna Hawk 10/17/2018 at 1:57 pm - Reply

    I think my AC is running a little slower than it should, and it’s good to know that the problem isn’t the AC size vs the heat. Getting a bigger system was something I was considering, but as you said, it would be inefficient most of the time if I did that, and I can see how getting it would make a problem with the humidity levels. I’ve tried your other suggestions like working with the thermostat and not running the clothes dryer, but it may be time, as you said, to get a maintenance check and ensure that there isn’t a problem causing it to slow down.

  11. Frank Shan 10/27/2018 at 3:13 am - Reply

    Thanks for your post. It helped me the lot. As I have followed all your blogs that had kept me at the best position in the industries.

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