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theoldwizard1 · 11-17-14, 10:27 PM

I can only tell you approximate numbers and something to watch for.

I have a 1400 sq. ft. trilevel. It has above average insulation and double pane thermo-windows (far from "super" insulation). Tonight, the outside temp is in the 20s. The wind gusting up to about 30 mph. It takes a 2 degree drop on my digital thermostat to trigger the "call" for heat from my 85% efficient horizontal furnace. Run time is less than 10 minutes. Off time is 10-20 minutes.

When it is EXTREMELY cold (below zero) and the wind is blowing hard my furnace DOES short cycle from hitting the over-heat limit switch. According to one service person (who I agree with), this is because the furnace has to run for a longer than typical AND the horizontally mounted furnace (mounted in the crawl space) does not allow "free flow" of air out and into the house. Warm air actually has to make 2 - 90° turns before it gets into the main supply duct.

With this combination of weather occurs, the inside temp can get down to below 64 even when the thermostat is set to above 72 ! Electric heat is the only way to get the temp up to 70. OR ... put on a sweat shirt and an extra blanket on the bed.

Blower speed is at maximum. Burner pressure is at minimum.

11-17-14, 10:27 PM	#17
theoldwizard1 Apprentice EcoRenovator Join Date: Oct 2014 Location: SE MI Posts: 105 Thanks: 3 Thanked 12 Times in 9 Posts	I can only tell you approximate numbers and something to watch for. I have a 1400 sq. ft. trilevel. It has above average insulation and double pane thermo-windows (far from "super" insulation). Tonight, the outside temp is in the 20s. The wind gusting up to about 30 mph. It takes a 2 degree drop on my digital thermostat to trigger the "call" for heat from my 85% efficient horizontal furnace. Run time is less than 10 minutes. Off time is 10-20 minutes. When it is EXTREMELY cold (below zero) and the wind is blowing hard my furnace DOES short cycle from hitting the over-heat limit switch. According to one service person (who I agree with), this is because the furnace has to run for a longer than typical AND the horizontally mounted furnace (mounted in the crawl space) does not allow "free flow" of air out and into the house. Warm air actually has to make 2 - 90° turns before it gets into the main supply duct. With this combination of weather occurs, the inside temp can get down to below 64 even when the thermostat is set to above 72 ! Electric heat is the only way to get the temp up to 70. OR ... put on a sweat shirt and an extra blanket on the bed. Blower speed is at maximum. Burner pressure is at minimum.