Will MPD Change Manometer Setting?

Will a MPD change my manometer setting? I have a barometric damper and I have the draft set to .04 on the manometer. If I would put a MPD in should I put it before the barometric damper or after it? By installing a hand damper will that change the daft setting when you damper the stove down? Thanks!

If you must put in a manual damper then put it before the baro -- that is, closer to the stove than the baro. You don't want the CO coming out of the stove, slowed down or blocked by a hand damper above the baro, so it comes out through the baro into the room.

Yes you probably can reduce the draft with a hand damper. Depends on the volume of exhaust trying to go up the chimney, and how tight the hand damper closes down the passage. I'm guessing you want to do this because your chimney is 300 feet tall and has so much draft that the baro can't reduce it enough, or it is running half-open all the time and sucking an excess of room air up the chimney?

An SF 250 has a built in heat exchanger, it already reduces the exhaust gas velocity some, and the big firebox needs plenty of air to burn well. One of the characteristics of the SF 250 is that it doesn't burn real evenly , and it has been reported that this is because of the very large area of coal being fed by a single 'spinner vent' in the ash door..

I'd be surprised if a Hand damper improves anything with that stove, unless like suggested above, the chimney is very tall and strong drafting... I'd still want to have a Manometer on the stove full time to watch that you didn't close the hand damper when the weather was creating a weaker draft. You then may lose the fire from too little draft.

Greg L
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Thank for the reply,
the reason i'm thinking about installing a hand damper is that I have the barometric damper set as low as it will go.02 I even added a little weight to it just to get it to maintain a.04 to.05 on the manometer. Which is pretty consistent. That keeps the flap on the baro just about wide open 95% of the time. Seems to be sucking alot of room air up the chimney. My chimney is a masonry with 8x8 flu in the center of the house it's about 25ft high. I'm thinking that a mpd would let me slow that down. I do have the manometer hooked up all the time just to keep a eye on it.

I think you can get hand dampers with different sized holes. The trick will be to have small enough bypass holes so you slow it down sufficiently, but not close it down so much as to be a hazard when warm days reduce the draft. It's good that you have the manometer so you can monitor results of your changes.

Now here's an alternative idea that is probably safer, and would definitely be more elegant and more fun. Don't know if it's feasible in your setup. How about providing outside air to the baro damper, say via a dryer-type vent and aluminum foil vent hose, and sealed to the baro inlet? That saves your warm room air. Somebody must have done this before .... ????

Also, you mention your baro is wide open most of the time. If one baro is over-taxed by your chimney you could install a second one in parallel. But if you feed the baro with much-colder outside air, that might reduce the total air needed to what one baro can easily handle.

I did think of running a fresh air intake to the baro. Which wouldn't be a easy task to do! A MD would be the easy way out I was wondering to if any one did it and if so how it worked out? If I would install a second baro that wouldn't decrease the flow but just divide the air up between the two baro's wouldn't it? Thanks for the input...

Razzler wrote:Thank for the reply,
the reason i'm thinking about installing a hand damper is that I have the barometric damper set as low as it will go.02 I even added a little weight to it just to get it to maintain a.04 to.05 on the manometer. Which is pretty consistent. That keeps the flap on the baro just about wide open 95% of the time. Seems to be sucking alot of room air up the chimney. My chimney is a masonry with 8x8 flu in the center of the house it's about 25ft high. I'm thinking that a mpd would let me slow that down. I do have the manometer hooked up all the time just to keep a eye on it.

Your barometric damper needs to be sized to the size of your chimney flue. So you need one or more dampers whose total flapper door area is approximately the area of your 8x8 flue. A damper that is too small will alway be open. It's is operating outside it's range of regulation. Look at the Field Control web site for design guidance.

Yanche wrote:

Razzler wrote:Thank for the reply,
the reason i'm thinking about installing a hand damper is that I have the barometric damper set as low as it will go.02 I even added a little weight to it just to get it to maintain a.04 to.05 on the manometer. Which is pretty consistent. That keeps the flap on the baro just about wide open 95% of the time. Seems to be sucking alot of room air up the chimney. My chimney is a masonry with 8x8 flu in the center of the house it's about 25ft high. I'm thinking that a mpd would let me slow that down. I do have the manometer hooked up all the time just to keep a eye on it.

Your barometric damper needs to be sized to the size of your chimney flue. So you need one or more dampers whose total flapper door area is approximately the area of your 8x8 flue. A damper that is too small will alway be open. It's is operating outside it's range of regulation. Look at the Field Control web site for design guidance.

I am using a 6" baro on a 6" prefab chimney and my baro is just about fully open all of the time also. I have the baro weight set at .02 and it maintains a .035 to .04 draft on my stoker stove. I also thought it would be nice not sucking all of that warm air out of the house. I also do not know how to solve this issue or if it can be solved. I too thought about a MPD.

Razzler wrote:I did think of running a fresh air intake to the baro. Which wouldn't be a easy task to do!

It also would not work. The baro damper MUST be fed from the room the appliance is in.

thanks Yanche,
You're right on the money, Field Control has a chart on there web site. http://www.fieldcontrols.com/draftcontrol.php (scroll down) I should have a 8" baro that would match my flu. However by installing a 2" bigger baro (that I would have to reduce down to a 6" pipe before it gets to the 8" flu just to install it)i don't think it will change the volume of air going out the chimney? the flap will just be open a quarter of the way compared to three quarters of the way. And with a 8" baro I would probable be able to bring the manometer down lower, but I see no reason to go lower then a .04 with my setup. Coaledsweat by Installing a fresh air intake from out side would that unbalance the room air pressure?

The amount of draft produced by the chimney is directly related to the temperature of the air or gases entering it. Feeding cold outside air to the baro damper will affect the drafting ability of the chimney, lowering the temperature excessively. The amount of room temperature air being pulled in by the open barometric damper is far outweighed by the draft regulation it provides to the appliance and the much higher heat production that results.
The only time there could be a problem would be a house with very little outside air infusion, little make-up air would not allow the baro to open enough and do it's job.

Razzler wrote: Coaledsweat by Installing a fresh air intake from out side would that unbalance the room air pressure?

You would replace room pressure with outside air pressure. The baro only works properly if it is at the same pressure the appliance is at.

coaledsweat wrote:

Razzler wrote: Coaledsweat by Installing a fresh air intake from out side would that unbalance the room air pressure?

You would replace room pressure with outside air pressure. The baro only works properly if it is at the same pressure the appliance is at.

And that as well, I was still half asleep, sorry.

The MPD will not effect the baro, however it will effect the overfire draft. Below you can see my quote from the MPD thread.

"What I did was check the draft at three separate places. First at the stovepipe, prior to the baro. Next, at the draft door on the combustion fan. And lastly, I checked the overfire draft. I tested each point with and without the draft blower going.

Open or closed, the MPD had no impact on the draft feeding the fire. This was true with and without the draft blower.
Open or closed, the MPD had no impact on the stovepipe draft with the exception of when the blower ran. Open, the draft would climb very high, very quickly. Closed, the draft would bump up slightly, stay fairly steady and rise very slowly over time. This would confirm what I thought earlier, that the boiler will run the draft motor longer at a lower load as it should.
Now comes the big surprise, the overfire draft. When testing it with the MPD open or closed it had no impact on the overfire draft, which I thought was rather odd. Then the blower came on. BINGO! the draft went neutral instantly. I watched it for a while and noticed that the draft was going positive as the blower continued to fan the fire up.

I don't know about all the other chimney/solid fuel units out there, but mine proves if you don't have an airtight unit with a decent draft, you can kill yourself. I don't want that to happen to anybody, so check everything and be safe. Learn as much as you can and get the tools you need to run these things right. Burning coal is supposed to be a warmming experience, not one that leaves you stone cold."

The MPD isn't the aswer. I'm just gonna stick with barometric damper for now. Thanks to everyone for the help!!