Preamble: Single stage, mid-efficient, no pilot Carrier Furnace. Furnace installed in 2008 when the house was built. Been working well aside from a fan replacement in Nov 2021. Furnace has had a somewhat high “heat rise” for a long time. Started having new issues in December 2023 with limit switch tripping repeatedly, which was causing short cycles, and making my ecobee thermostat give me an error suggesting a filter change. Removed filter completely, AND set my adjustable furnace fan to High Speed, was previously med-high. This got rid of the limit switch problem, but I don’t want to live my life with no filter, and thought other things may be at work. Decided that I must still have too much gas going in, causing too much heat. I don’t own a manometer, which is the pro tool used to measure gas pressure. However, I felt reasonably confident I wasn’t introducing any danger by using heat rise as a proxy for pressure.
Before I started today, I had a heat rise of 85F (70-155F), that’s above the recommended range for my carrier Furnace, of 40-70F. I used CLock positions to measure adjustment screw positions.
Here’s my process, with CLock Position, change from original, and Outlet temp. (assumed inlet stayed at 70F.
No filter, fan on high
only going counterclockwise
Original, 1 o clock, heat 155
11 o'clock (-2H), 148
3 o'clock (-10h), 140
Noon, (-13H), 130
9 (-16h), 128
6 (-19h), 123
Noon (-25h) 109, (absolute minimum!)
Go back tighter to 3 (-22h), 114 (getting close!)
Fan to Med-high, no filter
Same clock, 3 as above, 113
Brand new Merv 11 filter
Still 3 as above, 115
Tighter to 7 (-18h), 125 - DONE
This gives me a heat rise of 55F, nicely within, but on the low side of, the 40-70 recommended range.
I have requested ATCO to come give a site inspection, and I may still get someone to put a manometer on the gas to make sure pressures are good, but I would suspect the right heat is made by the right pressure in most cases.
Still having some occasional errors from the Ecobee, it’s possible my messing around with the fan wires knocked one of the thermostat wires loose. I will investigate that at some point as well.
Originally Posted by ThePenIsMightier
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