Furnace Question

[Tour 931]

I’ve noticed that the furnace on both my class A and teardrop fan doesn’t operate the same way as home furnaces I’ve had. The fan starts then after a few seconds they fire up. My home furnaces fire up and then when it’s up to temperature the fan starts. Anyone know why?

 

[GlampingOn]

Hmmm.

 

[Cary Winch]

Gene,

When you say the fan on your home furnace starts up do you mean the air moving through the ducts or the inducer blower? If your furnace has an inducer blower it must start before the furnace ignites. There should be a sail switch then that verifies airflow out the exhaust to show it works and there is no obstructions. On a home furnace the output blower starts then once a temperature switch is satisfied so that the furnace is blowing warm air only.

However on a RV furnace the inducer blower and the ducting blower are on the same motor. So, the first thing that comes on is the fan blower and sets the sail switch to assure that the exhaust is clear and the exhaust blower is blowing. Then the gas turns on and ignition starts while the blower is running. The thermostat basically operates the gas on/off to get the heat out. Once the gas valve turns off and stops the flame the blower will continue to run to clear the exhaust and cool things down for short duration.

So, really to sum it up. The compactness of a RV furnace dictates a common blower motor and shaft running two blower fans, one exhaust inducer and one duct blower. They start and run together and since the inducer is needed prior to ignition that is why you get air moving before the flame lights. Where as a larger home furnace will have a smaller blower motor for the exhaust inducer on the exhaust ducting and the much larger ducting blower is separate and can/will be operated as needed.

Cary

 

[Tour 931]

Gene,

When you say the fan on your home furnace starts up do you mean the air moving through the ducts or the inducer blower? If your furnace has an inducer blower it must start before the furnace ignites. There should be a sail switch then that verifies airflow out the exhaust to show it works and there is no obstructions. On a home furnace the output blower starts then once a temperature switch is satisfied so that the furnace is blowing warm air only.

However on a RV furnace the inducer blower and the ducting blower are on the same motor. So, the first thing that comes on is the fan blower and sets the sail switch to assure that the exhaust is clear and the exhaust blower is blowing. Then the gas turns on and ignition starts while the blower is running. The thermostat basically operates the gas on/off to get the heat out. Once the gas valve turns off and stops the flame the blower will continue to run to clear the exhaust and cool things down for short duration.

So, really to sum it up. The compactness of a RV furnace dictates a common blower motor and shaft running two blower fans, one exhaust inducer and one duct blower. They start and run together and since the inducer is needed prior to ignition that is why you get air moving before the flame lights. Where as a larger home furnace will have a smaller blower motor for the exhaust inducer on the exhaust ducting and the much larger ducting blower is separate and can/will be operated as needed.

Cary

Thanks Cary that answers my question. I didn’t know about inducer exhausts.