Furnace inducer motors

[Puddin' Man]

I've had a Heil updraft furnace installed in my little brick bungalow since 03-06. Standard-looking rig.

Sequence of ops looks like:

Tstat calls for heat inducer motor runs for a bit igniter heats up gas valve opens, burners fire igniter turns off blower kicks in

What can y'all tell me about the inducer motor? When is it supposed to run? Not run? What does it really do?

Furnaces didn't used to have inducer motors. When and why did we get inducer motors? Was it because of redesign of the heat exchangers?

In the context of design, are inducer motors really needed in modern furnaces? Or are they another bell-and-whistle that mostly just generates service /parts revenue?

Thx, Puddin'

"Blues starts to rolling ... stops at my front do'. I'm gonna change my way of living ... won't have to worry no mo'." - from "Blues Before Sunrise", Leroy Carr, maybe 1934

[John McGaw]

From what I've read the inducer motor really is necessary. The heat exchanger for the modern furnace is so convoluted and has so much drag that depending on mere hot air to start and continue the draft is not possible. Old furnaces could and did depend on the "hot air rises" principle to establish their draft but that only goes so far and not much air is going to wind up going through those little soda straw-sized passages in a modern heat exchanger unless it gets a bit of a goose.

[Don Young]

The inducer motor is what provides the draft for the burners. It reduces the heat loss out the vent which would otherwise be necessary for the draft. It is a good efficieny and safety improver, though it does add initial and service cost. It runs at the beginning of the heat cycle to purge any stray gas from the combustion area, continues to run while the burners are on, and runs for a short time after the burners go off in order to clear the fumes from the furnace.

Don Young

[The Freon Cowboy]

[Stormin Mormon]

What can y'all tell me about the inducer motor?

CY: Essential gadget.

When is it supposed to run?

CY: Starts before the ignitor, and ends about the time of the gas valve closing.

Not run?

CY: When gas valve is closed.

What does it really do?

CY: Moves flue gasses out of the heat exchanger.

Furnaces didn't used to have inducer motors. When and why did we get inducer motors?

CY: Eighties. Because the exhaust was too cold to float up the chimney.

Was it because of redesign of the heat exchangers?

CY: Only partly.

In the context of design, are inducer motors really needed in modern furnaces?

CY: Totally essential.

Or are they another bell-and-whistle that mostly just generates service /parts revenue?

CY: No.

Thx,

CY: Welcome.

Puddin'

[Stormin Mormon]

Flue gasses on new furnaces much colder. Not as much thermal lift.

[Stormin Mormon]

What he said. But he said it better.