Manual pipe dampers .. how, why, when

I don't know how I to direct this thread. While I have a certain history and feelings toward manual pipe dampers, once again, "I'm no expert".

Growing up, everybody that I knew, burned coal. Some had coal boilers, some coal hot air, some Warm Morning parlor stoves, some had "bucket-a-days" for domestic hot water, in addition to their other heating unit, some had only coal kitchen stoves, etc..

The thing that they all had in common, was that they all had manual pipe dampers (MPD). The automatic barometric damper was NOT anywhere to be seen. The baro damper seemed to come along later, when the oil burner was introduced.

The MPD was typically opened during coal loading of the stove, it was opened to get the fire "cookin'", it was probably opened to shake down the ashes ... to let the dust escape up the chimney. Once the fire was going good, the MPD was closed to some extent. This seemed to keep the heat in the stove and also controlled the burn of the stove. The MPD is typically smaller than the diameter of the stove pipe it's mounted in, plus there are holes through it's center, so even "closed", there was quite an area for hot gasses to get by it and go on up the chimney.

Fast forward: I put the addition on the house, with fireplace on the first floor and a flue to the basement room for ?? wood or coal. The fireplace works great! The basement flue has "issues". I couldn't burn wood, as I'd get a downdraft, when the fire got weak. Changed to a Russo coal stove, which was better. The installation instructions said to use a baro damper to "preserve the warranty" and to set the baro for a predetermined draft in the flue. However, it was very temperamental . .. sometimes kindling or newspaper wouldn't even burn. Then after getting it burning, I might find it had gone out, for no apparent reason, leaving the coal sitting there unburned. The next day the situation might be exactly the opposite, with everything working like a charm! ... Very frustrating.

Last winter, I did extensive remodeling, including a new floor over the old worn , drafty one. Generally, things seem to work better this year. .... but far, from what I remember about "the good old days".

So, early this season, I added a MPD, which IMHO, has made a big, positive difference. (I've been asked to insert "caution warnings" into this thread, where appropriate. I'm not sure where that would be.) The thing with burning coal is, "common sense is an important issue", but more importantly "lack of common sense" is a bigger concern. I believe, I'll add here, "that even good common sense, sometimes falls short, if you don't know what the hazards are"! The MPD shouldn't be totally blocking the pipe off, and if the correct size is installed, that shouldn't happen.

I'm going to stick another "CAUTION" in here. The following are my thoughts, observations, musings, etc., applying only to hand fired stoves.

I think, a baro damper serves to control the draft over the fire, only! Part of a stoves ability to burn properly, is based on the building's air availability for it. If a ton of air is entering the baro damper, to maintain the correct draft over the fire, both heat and potential combustion air are expelled. (The same as running a bath or kitchen fan). Without adequate combustion air, I think CO possibilities are stronger, than with a good combustion mix. I'm not saying to eliminate the baro damper! I have both installed.

I think, with the MPD closed a "sensible amount", there is less fuel burned and less heat expelled through the chimney. In other words, the whole system can be run cooler, while getting the same heat from the stove. Also, I believe the coal has a much cleaner burn.

I think, with the MPD closed a "sensible amount", the fire stays warmer and won't extinguish on it's own, leaving a "plate full" of unburned coal.

While I was "down the road" getting coal from the dealer, when I walked into the scale house, I felt the stove, which was idling along. The guy there, who wasn't super "old", but wasn't green behind the ears either, offered his thoughts, without me even asking. He said, "Hand fired stoves needed a MPD to work properly and efficiently. And they wouldn't work right with only a baro damper." I asked him about CO poisoning. He said, "Years ago, of his coal customers, there was one death and a couple taken to the hospital. One was due to the elbow on the back of the stove being blocked up and the other was due to a furnace or stove, which was rusted out. Both of these customers had been told about the smell and unsafe conditions."

Hand fired stoves can be as safe as any stove. But they are intended to be looked after on a regular basis. There are many things, which effect the burn and safety of a stove. ... the more of them, that you are aware of, the safer it will be. CAUTION! If you were to consider a MPD for your installation, understand it first and if possible, have somebody, who is familiar with MPDs, guide you along with it's operation on "your stove". All stoves, their operation, and burn characteristics are different.

CAUTION WARNING! Amen, brother! I'm new to coal this year, but i have a lot of woodburning experience. My coal stove installer put in both a manual damper and a baro. The baro is a cheap piece of junk and I have blocked it (discussed elsewhere). Lately I have been experimenting with the manual damper CAUTION! and I am astonished to report that EVERYTHING Dallas says appears to be true for my stove. Longer cleaner burns with significantly greater heat output from the stove. Less air over the fire (I can hear the difference when I damp it down a bit, because it audibly hisses in through the small secondary). My manual damper DOES have significant holes in it so even when in the closed position I can see no visible change in the fire at normal burn rates. Even so I don't dare run it "closed", but "sensibly" closed 45 to 60 degrees seems to help a lot. CAUTION!

P.S. I AM going to get a second CO detector, just in case....

Well, I'm no expert but I will relate my personal experience. I have a Harman MkI that came with the house I bought. We had always burned wood when I was a kid and used a MPD. The Harman had a baro damper but no MPD. I moved the stove and there was no room for a baro damper so I omitted it but never put an MPD in.

Burning, as you can imagine, was nearly impossible. I talked to my coal dealer about it and he advised me to put in a MPD.

For 5 years, I have run it with the MPD and have had exellent results. As was stated, there is a significant gap around the edge, with some smaller holes in the middle. I run it fully closed most of the time. I'm talking dead vertical. I have a CO/smoke detector on top of the mantle to be "safe" but so far have not had an issue. My house is "leaky" enough so maybe that's why I'm "getting away with it" so far but I don't see any reason to change.

Jpete, how often do you clean out the accumulated fly ash that accumulates around the bottom of the 'near vertical' manual damper? The damper restricts and slows the flow of exhaust and fly ash, so it will form 'drifts' of ash, just like snow drifts. I know this from personal experience.

Using a manual damper is like driving a Model T ford, you have to be aware of the throttle, load, manually set the timing for the quality of fuel, and watch the engine for overheating. A barometric damper is like driving a modern car, that does all the adjustments for you. A barometric damper is adjusted with a manometer,and will give very consistant draft over the fire.

Using a Manual damper without several CO detectors is playing 'coal-burning roulette'. I'm glad to hear you have at least one installed.

Greg L

Greg, Unfortunately, a hand fired stove is much like the Model T''s .. it needs to be fine tuned to run correctly. There is no automatic choke or cruise control.

You being a pilot, know exactly what I'm talking about and how it would apply to to a recip. airplane engine. You've got Carb temps to be monitored, power settings and mixture adjustments to be made. If these things are not addressed, fuel burn suffers, power suffers, speed suffers and safety suffers.

LsFarm wrote:Jpete, how often do you clean out the accumulated fly ash that accumulates around the bottom of the 'near vertical' manual damper? The damper restricts and slows the flow of exhaust and fly ash, so it will form 'drifts' of ash, just like snow drifts. I know this from personal experience.

Using a manual damper is like driving a Model T ford, you have to be aware of the throttle, load, manually set the timing for the quality of fuel, and watch the engine for overheating. A barometric damper is like driving a modern car, that does all the adjustments for you. A barometric damper is adjusted with a manometer,and will give very consistant draft over the fire.

Using a Manual damper without several CO detectors is playing 'coal-burning roulette'. I'm glad to hear you have at least one installed.

Greg L

I really don't get a whole lot of ash. At the beginning of the season, there is a little in the stove, on either side of the collar but very little beyond that. I have a unique setup. I don't know if I can explain it well but if you are familiar with the MkI, I have MPD right at the collar coming out of the back of the stove. From there, it's a 90* elbow and then a round to oval adapter. This is because the stove is partially inserted into my fireplace. The previous owner just ripped the damper out of the fireplace, smashed a piece of round pipe flat until it fit through the opening and that was it. I made a sheet metal plate to cover the opening and cut out an opening to fit the oval adapter. It's hard to explain but it seems to be working.

And a barometric damper is like using an egt guage to adjust your engine's mixture instead of leaning till it runs rough then richening it 'a bit'.

There is a reason the most stove makers state that they want a Barometric damper installed. It is easy for a stove to overfire when it is set 'just right' at 10pm and then 4 hours later the wind picks up, the temps drop and the draft doubles, causing the 'just right' air setting to be way too much air and the stove overfires.

With a barometric damper, the excess draft will be 'broken' or relieved at the baro, and the stove will have the same draft over the fire at 2AM as it did at 10PM. Why negate a safety item that makes the stove easier to use, and more consistant??

I have read and reread your first post here and I still can't see why or how installing a manual damper in your downstairs coal stove chimney could correct draft reversals, or increase draft. Heat is what creates draft in a chimney, even room-temperature air is sufficient to create a significant draft up a chimney. Just open the damper in a fireplace with no fire and test the draft with a candle.. the amount of air leaving the house pretty amazing..

So when you choked off your flue from a 6"or 8" open pipe down to a 1/4" gap around the edge of the manual damper plus the two holes in the center, you reduced the volume of air to maybe 10% of what it was. How can 10% of the previous hot air be able to create MORE draft??? Even if the air was say triple the temp of what it was before, then you have 30% of the heat as before the damper... It just doesn't make sense.

Maybe since you state that the fireplace drafts just fine, maybe it was pulling so much draft on the house that it caused the draft reversal in the other chimney?? Something doesn't add up.

A manual damper can have it's uses, but if the coal burners in the past decades had barometric dampers available, they would have loved them, why burn more fuel, and risk out fires and overfires when a simple device that requires no experience or expertice to opperate will do such a good job??

Greg L

Greg, Your lack of experience is showing.

You keep shouting that a manual pipe damper is "unsafe". Would you say that an airplane or a gun is unsafe ?

There are several stove manufacturers, which absolutely require a manual pipe damper according to their installation instructions. There are some stoves which have them built right into the stove casting.

LsFarm wrote:I have read and reread your first post here and I still can't see why or how installing a manual damper in your downstairs coal stove chimney could correct draft reversals, or increase draft. Heat is what creates draft in a chimney, even room-temperature air is sufficient to create a significant draft up a chimney.

I don't believe the MPD corrected "draft reversals". I believe that was helped through, possibly, sealing the floor with a new one. ?? ... Made the house act less like a chimney.

You say above that "Heat is what creates draft in a chimney". This is true, by the same token, adding a ton of cooler air through a barometric damper, will decrease the draft in that chimney. ... possibly to the point of "little draft". ?? I hate when that happens! ... the CO starts to roll out of every crack in the stove and the baro.

And if you read the chimney links, which I posted, you'll be aware by now, that room temperature air "Is not always sufficient to create a significant draft up a chimney".

If you have a forced draft unit, it will blow a lot of heat up the chimney without it. I have one and use it. It also acts as an ash meter. When you have to start opening it more to keep your draft up, its time to clean the flyash.

Dallas, I don't 'lack experience'. I've built wood and coal stoves. sold stoves, burnt solid fuel since I was a teenager, and that was many decades ago..

Manual dampers ARE unsafe. The cheap little tension or friction springs loose tension with heat and age, the 'perfect setting' on the manual damper slips in the middle of the night... or a lump of creosote or fly ash falls on the damper and does the same...

I ran properly designed airtight wood stoves for years without any damper, there is no need if the stove is designed right and has control of the incoming air.

I can't agree that 70* room air is not adequate to create draft in a chimney, if the outside air temp is 50*? maybe, but it the outside air temp is 30*? I'll start a fire in those conditions anyday. Plenty of draft.

The only way that a baro damper could eliminate or reduce the draft in a chimney because of cooling it down too much would be if it was in a stone cold room. 70* room air is plenty of heat to mix with a coal or wood fire's exhaust gasses.

You don't seem to understand how a barometric damper works... there is no addition of 'too much' room air till there is 'too little draft'. The draft is set with a manometer and it will maintain that draft, or close down if the chimney can't pull enough draft to exceed the setting. If you have a manual damper and a warm front comes through at 3AM, you need to get up in the middle of the night to open the damper or the reduced draft will allow you to have the CO 'rolling out of every crack in the stove and baro.

Lets think about this, cracks in your stove?? weld em or toss the stove. leaks out the baro?? not unless the house has more vacuum on it than the draft in the chimney can overcome... That's a house issue.

I'm glad for you that the manual damper you installed has apparently made your stove work better. But each and every chimney, chimney type, inside or outside, stove, new design or old design stove, quality of house, house location, elevation, prevailing wind, etc, etc makes each chimney and solid fuel appliance a unique situation. A properly set up barometric damper eliminates a handfull of these variables and makes the burning experience much more consistant and reliable.

Greg L

LsFarm wrote:You don't seem to understand how a barometric damper works... there is no addition of 'too much' room air till there is 'too little draft'.

Wrong! The more draft caused by a hotter burn or wind going across the chimney will increase the opening of the baro damper, thereby allowing more cold air into the chimney. In a "too little draft" situation, there should be no room air entering the baro damper! The baro damper is there to keep the stove draft throttled down to the preset numbers. Your manometer would be positioned between the stove and baro, not between the baro and chimney.

I just did a little experiment on my stove. I set the baro damper to "just flutter" with a good hot fire and the manual damper wide open. When I shut the manual damper, there didn't appear to be any change in the baro and it's slight flutter.

MPD and barometric dampers are two completly different animals that perform two completly different functions in two completly different methods. The baro doesn't change the chimney's draft, it limits its affect on the stove by bleeding room air to reduce its draw on the stove at a given setpoint by venting room air to reduce the draw on the unit's firebox. The MPD sets the overfire draft which generally is much different than the chimney's needs, usally .02-.03 lower than the chimney's draft. Stokers often have no need for a manual damper as the draft is engineered into it and/or it uses a blower. Most handfired units will be easier to operate and control with an MPD, I wouldn't run one without it.