# Barometric Draft dampers - Possibly useful?



## spirilis (Nov 13, 2011)

My understanding of barometric draft controllers so far has been that they are a very bad idea for woodstoves due to the potential for creosote accumulation from having cooler flue temps, although their utility for fossil fuel burners is well established b/c those guys usually don't have chimney fires from condensation of the flue gasses.

But after reading Jay Shelton's "Solid Fuels Encyclopedia" (btw, this man did a lot of lab work testing stoves/etc, and this book contains a lot of good theory about solid fuel burning) I'm starting to second guess that, mainly because he states the complete opposite--that dilution air from a barometric damper actually *decreases* creosote accumulation.

Except from the section (page 172-174) (fyi, I think "SER" refers to Shelton Energy Research, his laboratory):


> BAROMETRIC DRAFT CONTROLS
> 
> A barometric draft control (Figure 11-5) works on a very different principle.  It contains a hinged and weighted flap that is normally closed when the appliance is not in use.  During use, when the draft in the chimney exceeds a preselected value, adjusted by moving a small weight attached to the flap, the draft pulls the flap open.  This lets room air into the chimney.
> 
> ...


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## spirilis (Nov 13, 2011)

Bear in mind this book was written in the 80's, codes may have changed since then and a lot of the unknown "research needs to be done" points may have had their research done by now (and found to be bad).  I don't know though.  Maybe some more experienced folks can chime in.

The figures referenced in this text btw just show time vs. BTU output, without the damper the peaks are high (~40K BTU) and burn time low, 3 loads completing usable heat output by 5 hours, while the chart underneath showing performance WITH a baro damper shows peak output around ~28-30K BTU and usable heat up until around ~6-7 hours.


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## spirilis (Nov 13, 2011)

Also he did talk about manual pipe dampers right before this--the general consensus was that they are not strictly necessary for truly airtight woodstoves, but that some small percentage efficiency increase can happen while using them, as he found with one of his experiments, but his speculation for the reason was either changing the smoke flow patterns inside the stovepipe (i.e. maybe the smoke gets pushed to the skin of the stovepipe more) or changes in airflow dynamics inside the stove itself--by restricting fluegas flow but opening the air inlet to compensate, the inlet airflow patterns may change in a way that promotes more turbulence which can result in better combustion.


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## spirilis (Nov 13, 2011)

There was one last sentence in the baro draft section that I couldn't type due to the post length:



> Keep in mind that a barometric draft control is of no use in systems with a marginal draft since the control works by decreasing draft.


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## laynes69 (Nov 13, 2011)

From what I have read, the dilution of room air decreases the chances for condensation due to low flue temperatures. We run a baro, our furnace is EPA certified. There's little deposits in the chimney, even with the low temperatures. I would suspect if a wood burning unit whether a stove or furnace that doesn't incorporate a true secondary burn, stage 3 creosote can accumulate quickly. I ran a Baro on our old wood furnace. Even trying to keep a hot fire, I would remove 2 to 3 gallons of creosote every other month. After installing an EPA certified furnace, the chimney had maybe a quart of stuff after a season. There's an instant difference with one in both burn times and efficiency. But the statement about low draft is 100% correct. A baro doesn't have a 100% seal, so if draft is low already, a Baro will hurt performance. Our chimney is 32' tall with a 5.5" rigid liner, draft is too high without one. Our furnace has an automatic damper via thermostat so a baro keeps things consistent in the flue.


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## Stephen in SoKY (Nov 13, 2011)

Without a BD, my former basement install of a central wood furnace, the equivalent of a US Stove unit these days, simply could not heat my house. MPD was virtually useless since I couldn't be there to adjust throughout the burn cycle and to compensate for dropping night time temps and the resultant increased draft. In my case, 30 feet of triple wall, even though it was outside with no chase, simply pulled all the heat out of the stove before it could be transferred to the air jacket. Yes, it was an airtight stove, but even the slight bypass in place to keep the fire allowed in too much combustion air with such a great draw. When the thermostat called for heat, it was an overfire waiting to happen. The BD completely changed the stove and immediately turned it into a perfectly viable heat source. Granted, I kept the BD set to pull less room air in than I would have with a coal furnace, but it still pulled enough that I had to supply outdoor air after installing it. I burned good, well seasoned oak, ash and hickory and never had any significant creosote issues. With less than ideal wood perhaps I would have. I NEVER had any creosote accumulation on the BD itself. Seems to me if that's an issue, you lack draft to begin with and consequently have no need for a BD. Folks seem to forget the entire idea behind a BD is that you can ADJUST the amount of draft to a level that suits your needs. With wood fires you may not need as much alleviation of draft so you can simply set the BD to an alternate level of action.


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## laynes69 (Nov 13, 2011)

A barometric damper needs to be set with a manometer according to the manufacturers specification. Anything outside of this can cause problems. We didn't have the liner with the old furnace, that made a large difference.


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## Stephen in SoKY (Nov 13, 2011)

Edit: Came across the wrong way. Must have more coffee before posting.........


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## spirilis (Nov 13, 2011)

Of course a manometer is not a complicated device either (or doesn't *have* to be), the book shows a diagram of a typical homemade manometer with tubing and some wood plank to secure it with a ruler for measurement...


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## laynes69 (Nov 13, 2011)

I tried to make a manometer. In the end I spent 40.00 and bought one. I've used it to measure static pressure in my ducting as well as draft speeds. It's a valuable tool, and costs little compared to a service call from a hvac company.


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