Whats more efficient for AC and Blower Fan, lower temperature/fan auto or higher temperature fan on

air-conditioningenergy efficiencyfurnacetemperaturethermostat

This summer i want to be more efficient and save money on my AC usage because I can remember last year it was an disaster. For example, on a typical 100 degree day, the highest the temperature would read on the thermostat is about 85-86 degree around 5pm without any AC, all windows and shades closed. Last summer I set my thermostat to 81 degree and the AC will kick on right about 3pm when temp start to go above 81 degree. And then every 15 to 30 min. or so, the AC and fan will constantly turn on and off. I usually run AC for 4 hours from 3-7, then we open all windows around 8pm when nightfall.

Below are the options I can think of, which one is more efficient and cost effective?

  1. Set the thermostat at 81 degree and keep fan on for four hours.

  2. Set the thermostat at 79 degree and fan auto for 3 hours.

  3. Set the thermostat at 78 degree and fan on for 1 hour then wait another hour and turn AC back on fan on for another 1hour.

My system is Lennox G16 Q3-50 Furnace and I think a 1.5 ton ac outside.

Best Answer

Whatever you do, use the blower fan on auto only. The blower fan is ineffective for circulation compared to ceiling fans or to fans on stands or to box fans. If your ducts are in a hot attic, circulating air will pick up heat through the relatively thin insulation of the ducts. If your ducts are in the crawl space of a pier-and-beam foundation, then maybe using the blower on for circulation might do some good.

I am well into my 70s and can't stand being hot so my recommendation is to set the thermostat at 78 F and leave it there. We keep ours at 74 F and just pay what it costs. If you have standard thickness filters, change the filter once a month or two months at most. Let everyone (including the dog) enjoy life at a civilized temperature and humidity.

Where are you? What was your monthly kWh last summer, say for July?

Edit Our electric power use kWh (so you can judge the validity of my answer on your question) for two retired people who stay home a lot and don't travel much, share one automobile (~one tank of gas per month), electric kitchen range (never eat out), electric clothes dryer, gas water heater.

2016 electric power use kWh Mar 500 Apr 500 May 700 Jun 1000 Jul 1700 Aug 1950 Sep 1500 Oct 1000 Nov 700 Dec 600 2017 Jan 750 (space heating of garage for painting) Feb 500 Mar 500