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So I seem to be having trouble with my power bills (they've often been near $400 while other people in my area with a similar sized house usually get around $140), and I've isolated the issue to my air conditioner (I shut the AC off during the day one day and saw that my power utilization instantly went down, we have smart-grid so the power company reports on an hourly basis on a website).

At first I started sealing just about everything I could think of (made sure my doors closed tighter, sealed off my fireplace, and used foam insulation just about everywhere I could think of) to get a tighter air seal.

I also had my AC system serviced (they added about 3/4lb of Freon and cleaned the evaporator coils), and replaced my filters and cleaned the coils on the compressor outside.

In spite of this, I'm keeping my house temperature around 80 degrees (it's usually 92-97 outside right now), and it's making very little difference that I can see during the heat of the day. My ecobee3 is reporting that the system runs nearly non-stop in the afternoon.

The HVAC tech tells me that the system is doing just about as much as it can do, and what I have is what I have. My house is 2,100 square feet and I have a 4 ton unit, which he tells me is appropriately sized. I use the older R-22 style coolant as well (unit is about 12 years old).

Is there anything else that can be done to help with these high power bills? I know my attic is pretty hot during the day, and when the AC first turns on, it feels like the heater is turned on. I've thought about putting a fan and some duct-work up there to try and build a cheap ventilation system to try and cool it down some, but I'm not sure how much that would do.

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  • You're concerned about the heat in the attic; is it just that the heat is conducted down into the house, or do you have A/C components in the attic?
    – Daniel Griscom
    Commented Jun 28, 2016 at 15:47
  • I'm surprised that other people have a power bill as low as $140 when you regularly see 97 degree days, around here they'd be paying closer to $200 - $250. Are those houses similar in age as yours? New houses tend to be much better insulated than older ones. If your AC ducts have little or no insulation (especially the ones in the hot attic), insulating the ducts can make a big difference. Energy efficient window treatments (heat blocking drapes or blinds, etc) can also help by reducing the amount of heating from the sun.
    – Johnny
    Commented Jun 28, 2016 at 15:59
  • Insulate, insulate, insulate, seal, and consider upgrading to a newer more energy efficient AC. Also consider your windows compared to other peoples whose bill you are comparing, energy efficiency of window can be a huge factor. Also consider shades blinds etc.
    – Tyson
    Commented Jun 28, 2016 at 16:00
  • Most utilities offer "budget" plans, where the cost is spread more evenly throughout the year. I know that doesn't solve the problem, but it could help manage the costs in the mean time.
    – Tester101
    Commented Jun 28, 2016 at 16:05
  • Windows (as @Tyson says). If your neighbours have more shade over their windows, shut the curtains during the day, or face the other way with their big windows, the difference can be huge.
    – Chris H
    Commented Jun 28, 2016 at 16:25

1 Answer 1

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If the company that serviced your A/C is not able to give you the answer you are looking for, I would recommend trying another company to get more opinions. I would recommend you ask them to measure the air coming out of the A/C to make sure its at least around 30 degrees cooler than the ambient temperature. For example if it is 90 degrees outside, then the air coming through the ducts by the AC unit should be 60 degrees. If the difference is much lower than that, then your system might be working extra hard to achieve your desired temperature, keeping your monthly bill higher than normal.

It is hard to know for sure without looking at your unit, and your setup, but here are some reasons why your A/C bill can be out of control:

  1. Your house has poor insulation
  2. The thermostat switch is always on (can you find times during the day to not have it on? such as when you are at work?)
  3. Faulty AC Ducts such as blockages, disconnects, holes, etc.
  4. Inefficient AC Unit due to lack of routine maintenance
  5. Very Old AC Unit. As an AC unit ages so does its efficiency.
  6. Faulty thermostats
  7. Low refrigerant charge
  8. Refrigerant flow-related problem
  9. Bad compressor valves
  10. Dirty air filters
  11. Poorly insulated house, or air leaks
  12. Duct work that was not properly sized
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  • +1, but some of the things you're remarking on the OP mentioned addressing in the question and in the comments. That being said, and plucking from your answer, I'd emphasize points #1 (poor insulation), #3 (duct issues, particularly really old and/or uninsulated ducts), #11 (a leaky, unsealed attic) and #12 (issues with the duct design). Also.....this made me wonder, is it possible for the return air design to be the lone culpret?
    – elrobis
    Commented Jun 12, 2017 at 17:24

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