Hi my fan blower comes on and blows cold air at first then a...

Hi my fan blower comes on and blows cold air at first then about 45 seconds later the heat flames come on and then blows hot air, then after the blower shuts off it comes back on imediatly for about 10 seconds then shuts down. I recently had a new thermostat put on could this be a problem that maybe the it is the wiring because it was fine before that last year when i put the heat on

Most gas furnaces require a GAS HEAT thermostat to operate correctly. A gas heat tstat DOES NOT turn the fan on, the fan is turned on by a fan switch in the furnace which is actuated by heat or time delay. With a gas heat tstat the sequence of operation is:

1. Tstat calls for heat.
2. Gas burner lights.
3. After a time delay or when fan switch heats up, fan switch operates and fan comes on.
4. Tstat is satisfied.
5. Gas burner goes off.
6. Fan run until fan switch cools off or until time delay times out.


Sequence of operation of an electric heat tstat is:

1. Tstat calls for heat.
2. Fan comes on and gas burner lights. (Blows cool air until the heat exchanger warms up, could be 1 minute or more.)
3. Tstat is satisfied.
4. Gas burner goes off and fan goes off.
If the furnace has a heat actuated fan switch the fan will run until the fan switch cools off or until time delay times out. Fan may run at a slower speed in this case.

If an hvac company installed the thermostat, they should fix the problem at no charge to you, call them back.

With the electric heat tstat operation you describe why(what is the need for) the time delay and the fan switch. I realize that the time delay is present but why can't the fan be controlled only by the furnace fan switch. I just don't understand why the time delay should also be there. Safety? Thanks.