Baro Damper with Cat III oil boiler?

jrfiero

Does one need a barometric damper with a positive pressure oil boiler?

I had an oil pro in yesterday as part of the Mass Save weatherization project, and he measured CO coming into the basement from the baro damper when my Buderus G115-5 was firing. He recommended removing the damper. I have the pipe and tape, but am trying to confirm his recommendation before I remove the damper.

The vent goes into a ~21' masonry chimney with an 8" liner.

FYI, the CO reading was 29, not enough to trigger my CO detectors elsewhere in the basement or on the floors above, but none would be better.

The system has been in place for 10 years (I've only been here one winter) and I don't think anyone has previously recommended this. The system runs like a champ, but I do occasionally notice the damper open and interior air rushing out when the boiler isn't firing.

Oh, and I searched. Couldn't come up with an answer. Sorry if I missed it.

Thanks,
Jonas

Robert O'Brien

http://www.bosch-climate.us/support-center/download-center/downloads-for-buderus-products/manuals-for-support.html

jrfiero

Thanks, I have that manual. It says "If necessary, install a barometric damper in the flue system to
maintain the underpressure in the system or to meet code requirements."

Do they make baro dampers that seal, so that positive pressure can't blow exhaust into the dwelling?

Steamhead

If you're getting products of combustion coming into the basement because the barometric doesn't completely seal when closed, there is a problem with the chimney. No barometric I've ever seen seals completely when closed.

The "positive pressure" in this boiler only exists in the firing zone. You still need draft to pull the combustion products into the chimney.

Have the chimney inspected and repaired.

jrfiero

Thanks for the response.
Not to be argumentative, but how can positive pressure "only exist in the firing zone?" Doesn't the pressure have to go out the vent?
I can see straight down to the bottom of the chimney from looking in the top, liner's all good, and it gets draft when the burner is not firing.

TDR

You may want to check to see if you have enough, combustion air. I have seen a lack out combustion air, in my home, and on some hot water boilers. Where I work we have two 400 hp boilers, and the stationary engineer, cannot understand why the overhead door has to be open.

Steamhead

Read the manual. Page 18:

"After starting the burner, set breeching draft to -0.01 to
-0.02 inches WC using a draft gauge. The overfire pressure can be positive. If necessary, install a barometric damper in the flue system to maintain the underpressure in the system or to meet code requirements. Always install the draft controller in vertical position. Use a draft gauge when making adjustments."

The "breeching" is the point where the chimney connector ("smoke pipe") connects to the boiler.

jrfiero

Thanks for the clarification.
I do have a service scheduled in a couple weeks, I'll discuss this situation with the tech.
For now I'll leave the damper as-is.

Bob Bona_4

A baro damper is used on single wall pipe. Nothing on single wall pipe is sealed- the elbow joints, the pipe seams all leak. A sealed baro wouldn't make any sense.

STEVEusaPA

I would follow the advice of Steamhead regarding chimney and TDR regarding combustion air.
Describe the entire venting from the boiler to the chimney-size, elbows, tees, distance from boiler to chimney base. Total height of chimney, diameter, interior or exterior, north facing, anything within 10 feet of the top of chimney, etc.
Take/post a pic of the piping from boiler to chimney, and an exterior pic of the top of the chimney.

Jamie Hall

Some installations -- it depends on the chimney -- have a damper on the breeching as well as a barometric damper. The damper on the breeching, together with the air shutters on the burner, controls the draught through the boiler. The barometric damper, then, serves to reduce the negative draught from the chimney which might upset the draught through the boiler.