More furnace help.

[Fish along]

I have an older lennox furnace in my garage that runs ok and when it fires up and runs its regular cycle and shuts off a short time later the fan will come on and blow for another minute or so,any ideas what might be doing this?Thanks.

[1886]

Sounds like it is cooling off the fire box. But I’m not a plumber.

[Sooner]

My mid range house furnace does this, I was told to make sure any exhaust gases get out of the pipe and into the outside air.

[Big Grey Wolf]

Main furnace fan is suppose to stay on for a few minutes and remove all the heat from the furnace and plenum to give best high effeciency. A fan coming on after cycle does not seem normal, small fan comes on at start of cycle to clear gases out.

[Dewey Cox]

Fan switch probably needs a little adjustment, if I had to guess.