What is a Barometric Damper?

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What is a Barometric Damper?

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numerouno

I am a building engineer and entered the HVAC trade in 1985. I have been the primary operator of a small water boiler for about 6 mos., I estimate the size of the building at about 40k sq. ft. I don't know the BTUs of the boiler but it is about 5'x6'x4'. It is an induced-draft fire-eye. What I see is that some 60 years ago, the "Field" brand barometric damper was installed upside down. Whaaaat?!!! I guess nobody cares. Just seems silly. My client has deferred a lot of building maintenance already. Why fix it now? To make it more confusing, the "Field" brand decal was placed upside down on the damper. All I can figure is that the installer could read, but didn't know squat about barometric dampers. Don't they put the decals on at the factory?

Mad Dog_2

Great explanation Ray. I think it's safe to say most, average installers, install them only because they have to. They put it in and walk away without understanding how they work. Mad Dog

Steamhead

You sure it's upside down? Some Field designs look that way but are actually correct. Take a pic of yours and post it, and we'll be able to tell you for sure.

billtwocase

If it was installed upside down, it would be open all the time

maxtech

340kw gas fired hotwater boiler chimney dia 250mm but horizontzl height 40 mtr how can we calculate id fan forthis flow rate of flue gas 109kg/hr flue gas temp 167 C

JohnNY

Thanks for this, Ray. I love to read your articles.

RayWohlfarth

Thanks for the feedback guys. I shake my head every day at some of the stuff you see installed. I have seen people wire them closed or somehow the weights disappear.

Mark Eatherton

Great article Ray. When people don't understand how they work, they either put way too much weight on them, or as you noted, wire them shut. They do this to keep carbon monoxide from "leaking" out.

Thanks for continuing to educate our industry.

ME

RayWohlfarth

Thanks Mark Hope all is well

hot_rod

Nice understandable article, Ray thanks.

Here is another approach that the European pellet boiler industry uses. A much higher quality stainless steel assembly, tight gasket seal, and of course $$.

RayWohlfarth

Bob Thats a nice looking unit. I still can figure out why its ok to have a stop on a fuel oil barometric but not a natural gas. It has to allow spillage. Wasn't sure what they were thinking when then wrote that code

ChrisJ

RayWohlfarth said:

Bob Thats a nice looking unit. I still can figure out why its ok to have a stop on a fuel oil barometric but not a natural gas. It has to allow spillage. Wasn't sure what they were thinking when then wrote that code

With an atmospheric appliance you have two options with a downdraft or blocked flue.

1: Allow the damper to swing open and vent combustion products with 0 or close to 0 PPM CO into the room. The spill switch then has time to react and shut the burner down.

2: Do not allow the damper to swing open which will starve the burner of O2 and cause it to still spill into the room, only now with a ton of CO because it's starving for air.

The double swing barometric is far safer. It allows the burner to operate normally during a blocked fuel or down draft situation just as a drafthood does. Allowing combustion products out into the room and fresh air into the burner.

RayWohlfarth

Thanks for the lesson Chris

ChrisJ

RayWohlfarth said:

Thanks for the lesson Chris

Just returning a little of what I've learned on HeatingHelp over the years.

Mark Eatherton

ChrisJ said:

RayWohlfarth said:

Bob Thats a nice looking unit. I still can figure out why its ok to have a stop on a fuel oil barometric but not a natural gas. It has to allow spillage. Wasn't sure what they were thinking when then wrote that code

With an atmospheric appliance you have two options with a downdraft or blocked flue.

1: Allow the damper to swing open and vent combustion products with 0 or close to 0 PPM CO into the room. The spill switch then has time to react and shut the burner down.

2: Do not allow the damper to swing open which will starve the burner of O2 and cause it to still spill into the room, only now with a ton of CO because it's starving for air.

The double swing barometric is far safer. It allows the burner to operate normally during a blocked fuel or down draft situation just as a drafthood does. Allowing combustion products out into the room and fresh air into the burner.

Chris, In my 40 years of spelunking around boiler rooms, I've witnessed a zero CO condition in the flue gas stream once. And I have no explanation for why it was at zero. Plus, the flue gas would be heavily laden with carbon dioxide, which will cause a flame to burn incompletely, causing a huge increase in the CO being spilled into the room.

I am curious as to wether you actually read this somewhere, or if it is conjecture on your part.

I agree with Ray's point, why is it OK to do on an oil boiler, but not on a gas fire appliance?

Make no sense.

ME

ChrisJ

> @Mark Eatherton said:
> Bob Thats a nice looking unit. I still can figure out why its ok to have a stop on a fuel oil barometric but not a natural gas. It has to allow spillage. Wasn't sure what they were thinking when then wrote that code
>
>
> With an atmospheric appliance you have two options with a downdraft or blocked flue.
>
> 1: Allow the damper to swing open and vent combustion products with 0 or close to 0 PPM CO into the room. The spill switch then has time to react and shut the burner down.
>
> 2: Do not allow the damper to swing open which will starve the burner of O2 and cause it to still spill into the room, only now with a ton of CO because it's starving for air.
>
> The double swing barometric is far safer. It allows the burner to operate normally during a blocked fuel or down draft situation just as a drafthood does. Allowing combustion products out into the room and fresh air into the burner.
>
>
>
> Chris, In my 40 years of spelunking around boiler rooms, I've witnessed a zero CO condition in the flue gas stream once. And I have no explanation for why it was at zero. Plus, the flue gas would be heavily laden with carbon dioxide, which will cause a flame to burn incompletely, causing a huge increase in the CO being spilled into the room.
>
> I am curious as to wether you actually read this somewhere, or if it is conjecture on your part.
>
> I agree with Ray's point, why is it OK to do on an oil boiler, but not on a gas fire appliance?
>
> Make no sense.
>
> ME
Mark. I read it, though it's been about two years.
I suppose I could've confused things since then, but I don't think I have.

Atmospheric appliances do not rely on draft from the flue and should burn cleanly without it. This is why some feel drafthoods are dangerous, they uncouple the flue from the appliance, completely.

I've done zero testing my self and wouldn't recommend anyone try to do testing on the subject, but they claim a draft hood is designed to allow proper combustion during a blocked flue or down draft.

I believe a double acting barometric is the same principle. It swings outward to relieve a downdraft or even a blocked flue to attempt to allow the atmospheric burner to operate normally, or, as close to it as possible under those conditions.

It also allows a spill switch to function.


@captainco and @Tim McElwain are the experts on this subject.

Mark Eatherton

Was it this report?

http://www.ahrinet.org/App_Content/ahri/files/RESEARCH/Technical Results/Final_Report_Gas_Interchangeability_March-2-2010.pdf

Harvey Ramer

Nice article Ray.

I just ordered a gas tight draft regulator from Westwood. It's for a wood boiler, gasifier unit. The thought is to keep it from puking out fine ash and combustion gasses when the second stage is igniting.

RayWohlfarth

Thanks Harvey
One of the things I have seen is any change in the combustion process seems to cause a spike in CO in the flue gases, even going from low to high fire or back. The other thing is many places do not require a spill switch for their barometric damper which is scary as well.

Skepticelt

Well written article. Thanks for taking the time to help others understand the barometric damper.

captainco

Barometrics were first created for wood and coal devices. There were no pilots to blow out, no controls to shut things down. Hopes were that if the equipment wasn't venting and the flue gases were trapped inside the flame would get snuffed out.

When oil equipment came out the only barometrics being made were single acting and therefore that is what was used. Once the double acting barometrics were invented, they should have been used on oil. Ever noticed how the single acting barometric slams shut every time the burner lights. This can cause blow back into the burner tube. Of course I have never seen a single acting barometric keep a house from sooting up from oil. If they were double acting with spill switches we could solve at least two major problems!

Double acting barometrics did not come out until the late or early 30's for gas equipment. Drafthoods were non-existent. Single acting barometrics were used which was causing major pilot outages from downdrafts.. The drafthood was created before the double acting barometric, to keep pilots lit.

The drafthoods original main function is to minimize nuisance calls to utilities to light pilots. No concern for the consumer other than they would die warm and clean. Any device that allows equipment to operate with a plugged flue is ridiculous!

The combustion process has two main elements, fuel and air. Which of these need to be controlled? Both!!
What controls the majority of air to the burner? The amount of air that enters a burner (not the majority of air but some on power burners), is determined by how fast the flue gases escape the equipment. The force that determines how fast flue gases escape is draft. Drafthoods rely on buoyancy and random selection because they disconnect equipment from the draft in the flue. They have no ability to regulate. They connect equipment to the building instead of the flue. Remember drafthoods were created to keep pilots lit and there are few standing pilots today plus there is spark ignition which kind of makes drafthoods obsolete. If one would monitor all the CO poisonings that occur daily they would find the majority are by drafthood equipment.

Anyway, because draft is constantly varying with environmental conditions, the odds are that venting and combustion air will be affected. No regulation of air is not conducive to safe and efficient combustion.

What creates draft? Cold air displacing hot air. That is why draft is higher on colder days. That is why draft is higher in taller flues than shorter flues, more cold air exerting a force. Drafthoods usually cool flue gases 40% more than barometrics before they enter the flue. If temperature difference creates draft, is cooling the flue gases a benefit or a detriment?

Double acting barometrics with safety spill switches should be used 100% on all negative venting flues. This would allow oil furnaces to shut down before they soot up the house in many cases.

Typical residential gas equipment requires -.02" W.C. to vent properly. Oil usually requires -.03" W.C. Wood and coal about -.05"W.C.
Commercial and industrial equipment have their own draft requirements.

Good article Ray, just thought I would add some additional insight.

RayWohlfarth

Thanks All
It still amazes me how barometrics are allowed to be installed with a spill switch. There are lots of things I dod not understand in our industry

captainco

Ray, I hope you meant without a spill switch.
Yes, there are too many things in our industry that don't make sense.

RayWohlfarth

CaptainCO LOL Yes Senior moment Spill switches are not required here. Boggles my mind.

Mad Dog_2

It's insane. Always wondered why oil burners never had them. Once I learned boiler wiring, I'd add them in. Mad Dog