My electronic air filter just died and I substituted a replacement type air filter. Is there a normal average or rule of thumb to determine if output temperature is excessive on a gas-fired furnace? I know there are devices to prevent over heating but I just wondered if this filter was blocking airflow. The output is 150°F.
I read my temp in my manual, but how do you read it on the furnace. I put a probe just above the furnace under the AC coil and found I has to hot. I believe your question is good and overlooked since higher than the range specified would shorten the exchangers life. I have a lennox condensing with a plastic coated aluminum I think, Its not known to last so I had it lowered.
I drilled a small hole into a duct at the top of the furnace and inserted a temperature probe similar to a meat thermometer. My manual gives the temperature rise but not a maximum.
Shouldn't matter. The filter is usually placed in the return plenum before the burners. So the air passing through the filter is just room temp, not the furnace temp.
The air should be twenty or so degrees hotter than the return air. Sounds like you have too little air flow.
I'd want to measure about three or four feet away from the furnace. Not right above it.
Gosh, 150 is a bit hot. Even in a large home, that might make the hot air out of the register maybe above 135 degrees.
If your furnace has a multi-speed fan, I would suspect a problem there. A fresh replacement filter not so much.
Yes, I understand that air flow volume and speed will affect the amount of heat transferred from the fire box heat exchanger, and you suspect the speed and the air volume has been reduced by the air filter. I presume the furnace fire box has a upper temperature limit control, and it is working order. Just not kicking in.
I also presume you have taken the temperature with, and without, the replacement filter in place. And the result is very little temperature difference with and without the filter. (10 minutes or so with a filter won't hurt.)
There is a design temp rise or output range, he is not talking about register output.
What are the number ranges it states, I forget but I think I was lower.
What the specified rise? What's the input air temp?
Is the input air temp + the specified rise
Thank you for your replies. The furnace is a Carrier Up-flow Gas-Fired Natural-Draft model 58GS100CB installed in 1989 with a 2½-ton air conditioner. It is located in the basement of a small tri-level, 1000 sq. ft. home near Chicago. The Temp Rise Range is rated 45-75. When installed, the multiple speed blower was pre-set with jumpers to low for heat and high for cooling.
As close as I can determine the temperatures in Fahrenheit are, basement ambient air in the room with the furnace 77° the thermostat located on the above ground level 74°. The input duct at the filter 80° and output duct to the above ground floor level 140°. The output remained within about a degree or two with or without a filter. I do not now if this is normal, as I never measured these until I replaced the electronic filter with a substitute paper type.
As the temperature is the same with and without the filter I assume the airflow is not blocked but I do not know if this is too high?
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