Oil Boiler Barometric Damper

[Jon mackay]

When looking at the barometric damper on an oil fired boiler or furnace, how would you know if the counter weight is adjusted properly?

I will make sure that it swings freely and is not obstructed, but usually I will see the damper open slightly when the system fires.

I was not sure if the colder weather (25-30 Deg. F) would stop it from opening when firing.

This particular unit had an obstruction at the bottom that prevents it from swinging out but it looked as if it were a part of the vent.

Crown Boiler mfr. in 1997
Model # BD 120 LC
120,000 BTU

Any info would be helpful..

[Garry Sorrells]

Blow on it or very sight tap on bottom.
Exterior temp should have no effect on damper operation after unit is fired and running.
Yes there is a stop at bottom.

[James Duffin]

The only way to tell is with a draft guage inserted in the flue. Just because it moves freely does not mean it is adjusted properly Typically draft measurements around -0.02" w.c. are considered "low", and around-0.06" w.c. are "high" draft levels...... but not always.

[H.G. Watson, Sr.]

Combustion analizer, draft gauge measurements from the chamber and breach, inspection, cleaning/adjustments as necessary, and testing.

[Darren Miller]

First make sure the weight is installed on the proper side
V- vertical
H- horizontal.

[Joe Arcaro]

Why do boilers need barometric dampers, and not furnaces, water heaters, etc? What is the function of the damper? What if a direct vent boiler has no damper?

[Darren Miller]

It's not the boiler; it's if the appliance is oil fired.

[H.G. Watson, Sr.]

Joe A,

Fuel oil fired appliances utilize one-way dampers to assist in draft, and avoid run-away temps in the vent or chimney from the combustion chamber running away at the burner. Most domestic/residential fuel oil fired furnaces, water heaters, boilers, etc. have them.


Should the wind be blowing or pressure differential the barometric damper properly adjusted will close, avoiding spillage.


Gas fired appliances may be draft hood (cat I) which functions as a two-way or allows spillage - or if fitted with a baro damper it too would be two way. You may also have a manifold or a firing sequencer if there are multiple appliances.


Baromeric dampers are draft assistance/modulating devices.


Other solid fuel devices may also have a damper, it may or may not be automatic.

That's not the end-all, but a simplistic generalization.


HTH