"Phil-In-Mich." wrote in message
...
"Sudy Nim" wrote in message
...
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.


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.)

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?