damper on fan assist flue

Is this damper necessary?

It hinges easily when touched…

Its located between the furnace and the fan assist blower.

(The blower is located at the flue end where it exits the crawlspace.)

The blower has control wires that appear to be wired to shut off the unit if the blower quits.

Sept27 028.jpg

That’s commonly called a “Field control”, which is a slang term derived from the main manufacturer of such devices. It’s weighted, and used to control the over fire draft of fossil fuel burning appliances. It maintains an even draft, without regard to how many appliances are operating or how hard the wind is blowing outside.


If it’s a barometric draft damper I don’t see the weight or it’s adjustment.

**7M Field Draft Control **

For oil or coal fired residential heating applications. Designed for settings from 0.01" to 0.1". Features an infinitely variable screw adjustment. Employs side wings to control air direction with gate curvatures designed to compensate for differences inhorizontal and vertical settings. This 7M Field Draft Control is one of many top quality items in our Stove Pipe Fittings - Black department.


Thanks, this page looks like the one, see 2nd page down, rt side picture showing the supplemental air intake


That would make sense in your case, since you had a power venter on the end. Probably needed that to keep from sucking some crazy high over fire draft at the furnace. That Field control probably tilts open a wee bit when the drafter motor turns on.

Some barometric dampers have the adjustable weights on the inside of the damper.

Some you adjust by turning the whole damper so the axis is on an angle.
They work just as well as the ones with adjustable weight.
. Cookie

Thanks, I haven’t seen the other types yet.