Quote:
Originally Posted by oil pan 4
The fan was cycling on and off?
Something is very wrong.
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It only cycles on and off when I'm trying to heat the house to a low temperature like 40*F. When it's above 60*F it's fine and doesn't cycle on and off. I also conducted some similar tests at temperatures between 50 and 60*F and didn't notice as much of an improvement in efficiency like I did at 40 to 50*F. Between 60 and 70*F the furnace just stays on without any cycling so there's no difference in efficiency by hardwiring the blower on during that time.
My take on it is that the furnace is designed to run efficiently at around 70*F. The idea being that if the air going into the furnace is 70* it will have heated up to 110* by the time it reaches the switch. But if it's 40* it will not have heated to 110* and so turns off the switch. For it to work the same the temperature difference should be the same because the air is only going to increase by about 40* or so by the time it reaches the thermoswitch.
Basically this:
House/Thermoswitch
40*/80*
50*/90*
60*/100*
70*/110*
80/120*
90/130*
So if the house is at 40* the thermoswitch should be at 80* because the air will only heat up 40* more than 40* by the time it reaches the thermoswitch.