[gumby79]

I have the same problem with short cycling we share the same component at fault and it's in the design of the Furnace.the part # is 90 - 15 F. translation 90° on reduce 15° off and F you get that one. Yes the fire is cooling off the Firebox by 15 degrees telling the system that it is safe to turn off the fan because the fire is been extinguished an adequate period of time to reduce the heat soak and chances of thermal cycling causing cracking from uneven Cooling. My furnace is a Coleman. I first discovered the problem when I Eco modded the furnace upon my arrival at the new house. I added a duct to the face that made it pull cold air from the floor instead of the hot air off the top where the air filter is. This changed the Dynamics of how the machine was operating and would cause the heater to short cycle adding a restriction to slow down the air flow rate put a bandaid on the problem. This was more efficient in that they furnace was able to maintain air flow over the heat exchanger from flame On to flame Off instead of having the fire on continuous and stopping the fan every 3 minutes for 5 minutes( this made it hard for me to sleep as the furnace is on the other side of the wall from my bed and Mobley homes they are no good for slowing down sound much less deadening any) I call it a Band-Aid because adding a restriction in front of the blower motor causes the motor to consume more watts producing heat energy he just heat so this is not the loss but the reduced service life will take a toll eventually it's already 30 years old.
Regardless of the ducting or not too cold of air cools the fire off too fast setting 55°f is too far outside the normal design parameters. I want to set it for 40° when I'm not home only enough to keep the pipes from freezing. The other type of problem I had was the bi-metal spring thermostat headstone spring amathing one too many times. And I wanted a digital programmable thermostat. So I bought a Honeywell 5 + 2 $20. This worked great so long as you didn't mind the Blasted thing coming on every 15 minutes massive downgrade from the broken by-metal. I determine the problem was the window of operation is too small on one degree below set off one degree above set basically by the time the air settles out from having been warmed and cold things suck heat out of it it's time for it to come back on. So I called Honeywell the manufacturer, who basically told me suck an egg this is what we build we're not going to give you enough specifications on the internal workings of our product for you to reverse-engineer /adjust the hysteresis setting. But I got a good technician one who was patient and could follow those path I lead. The thermostat has two settings on the backside little dip switch position A electric or gas furnace position B hydronic/ boiler. I was able to get the information from the tech that yes indeed electric and furnace are set + -1 degree. And hydronic is set + -3 so now I run my gas furnace in hydronic mode giving me a slightly wider window of soak time and a light duty automatic pulse and glide.
When I bought the house I also bought a pellet stove used from Craigslist $500. On low it will activate the blower motor on the furnace when it gets above zero outside for too many hours in the day with the stove set too low. So above 0 I start the stove in the evening and let it run through the night and turn it off in the morning ~65-85°f . Max 1/3 bag(40lbs bag. ) per day with a high above 0°f. I had 28of 50 bags (1 ton)at the start of the next heating season .
I was out of town this spring when we got a hot spell in Montana whopping 80° with the insulation value in the house I got and heat produced from three pilot lights and one refrigerator this caused the inside temperature to exceed 90 degrees and stay there for days on end,$150 bill ouch. The inside never droped below75° so it just sat there circulating the hot air with no call for heat.