Thread: House AC Temp
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Old 06-14-2021, 09:41 PM
John V. John V. is offline
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When I lived in Fla, I kept an analog thermometer pierced into the return box just ahead of the filter and another just after the evap coil. I would get about an 18 F differential which HVAC techs told me was what I should expect. I kept them in place so that whenever I suspected an issue, the temp differential provided the data.

Original heat pump (basically an AC unit with a reversing valve to provide heat in winter) was from 1994. I replaced it around 2007 with a much more efficient (at the time) unit. After seeing a substantial reduction in my electric bill, I realized I was stupid for limping along with a failing unit that needed freon every several months that was getting expensive (old freon) at the time.

That unit failed around 2018 just after the 10 year warranty expired (partly my fault because it actually had started acting up a year earlier but I ignored it because I forgot I had the 10 year warranty).

The 2018 unit was even higher efficiency but the utility savings were not noticeable as the percent increase in efficiency was not nearly as big as it had been in 2007.

Moral of the story, if your unit is pre-2000 and you use the AC a lot, you may find that the payback on a new unit is relatively short based on electric savings. Up north might not be as dramatic as your AC will run less often. In the '80s and '90s, living in the Chicago 'burbs, we rarely turned the AC on.

Here in the mountains now, my original to this house 1999 unit is still running fine and since we haven't yet had to run it this season, hard to justify a replacement although my plan is to replace it with a heat pump as I believe it may be cheaper for electric to run it for heat above 35 F ambient than my high efficiency condensing furnace that runs on propane at roughly $2/gal. I would run it as a "dual fuel" system to manage my utility costs to best advantage.