Exhaust Heat

I apologize if this has been brought up before, but my searches have come up M/T. It concerns the comparisons pertaining to MPDs vs baros. 1st off, is it true that the stove pipe exhaust carries heat up the chimney? I would think this is a given. I'm also aware that the draft is critical to stove performance. I've heard of discussions explaining if an MPD is closed down, you can extract more heat from the stove due to limiting the heat loss up the pipe.In the baro application, is it possible to have this feature, when the component is basically adjusted for a specific draft? The little I've been able to experiment with my stove, it seems when the MPD is more in the closed position, my heat exchanger temp goes up. There are many other variables that cause this to happen, so I can't say 100%, that this is as it appears. Is this considered the ABCs of solid fuel burning, and my "green-ness is shining through? ... Just curious.

joeq wrote:The little I've been able to experiment with my stove, it seems when the MPD is more in the closed position, my heat exchanger temp goes up.

Are you referring to a heat exchanger in the flue? If so, this is quite interesting. Maybe closing the MPD (to a point) causes in increase in the velocity of the exhaust gases going up the chimney.

Have you checked this with your MPD in the completely closed position?

Because your stove has a thermostat it will compensate for a too strong draft and close down the air intake. This is under normal conditions. If you are running the stove flat out with the thermostat set high and with high stack temperatures, then a manual damper might help to slow the flue gasses enough to raise the temperature in the heat exchanger and lower in the flue pipe.

With the thermostat set very high it reaches a point at which it never is able to fully close the air intake and is acting more like a manual control.

LDPosse wrote:

joeq wrote:The little I've been able to experiment with my stove, it seems when the MPD is more in the closed position, my heat exchanger temp goes up.

Are you referring to a heat exchanger in the flue? If so, this is quite interesting. Maybe closing the MPD (to a point) causes in increase in the velocity of the exhaust gases going up the chimney.

Have you checked this with your MPD in the completely closed position?

i think he meant to say combustion chamber or maybe he has a heat exchanger around his combustion chamber?

@LDposse... yes indeed these are some of the abc's, ideally you would get a manometer and set your draft around .06 WC, back in the day we used manual dampers which I always liked better but times have changed

dcrane wrote: @LDposse... yes indeed these are some of the abc's, ideally you would get a manometer and set your draft around .06 WC, back in the day we used manual dampers which I always liked better but times have changed

I have an MPD, but with my DS having the bi-metal t-stat, I just leave the MPD wide open.

I know most people want to keep more heat in the stove, but I have an interior chimney, and it gives off wonderful radiant heat all the way through the 2nd story of the house. Another plus of burning bituminous in my case. With anthracite, a roaring fire will get me 200° stack temps, I can get the same with a mild to moderate fire using bit.

LDPosse wrote:

joeq wrote:The little I've been able to experiment with my stove, it seems when the MPD is more in the closed position, my heat exchanger temp goes up.

Are you referring to a heat exchanger in the flue? If so, this is quite interesting. Maybe closing the MPD (to a point) causes in increase in the velocity of the exhaust gases going up the chimney.

Have you checked this with your MPD in the completely closed position?

My heat exchanger is wrapped around the fire-box and is one of the benefits of this stove in extracting as much heat as possible. I've thought of closing the damper all the way, but as of yet haven't been "brave" enuff.

franco b wrote:Because your stove has a thermostat it will compensate for a too strong draft and close down the air intake. This is under normal conditions. If you are running the stove flat out with the thermostat set high and with high stack temperatures, then a manual damper might help to slow the flue gasses enough to raise the temperature in the heat exchanger and lower in the flue pipe.

With the thermostat set very high it reaches a point at which it never is able to fully close the air intake and is acting more like a manual control.

My adjustable thermostat has a "reference" knob for temperature.It ranges from the numbers 1-9. It is so sensitive that I only run it from 1/2 (before 1) to 1 1/2.
If I ever need extreme heat, maybe 2, but I have needed my coals to be white hot. The intake damper funtions as it should, and the only time it is wide open, is when the coals are going out and is calling for more air. I never run my stove wide open.
As for my question concerning baro-dampers, can they be used to retain any heat from escaping through the chimney, or is this not a common practice or need?

They stop excess draft which in a manual air intake stove can cause the stove to burn hotter than wanted raising stack temp. With your stove the thermostat will sense the hotter stove and close down the air.

joeq wrote:

LDPosse wrote: Are you referring to a heat exchanger in the flue? If so, this is quite interesting. Maybe closing the MPD (to a point) causes in increase in the velocity of the exhaust gases going up the chimney.

Have you checked this with your MPD in the completely closed position?

My heat exchanger is wrapped around the fire-box and is one of the benefits of this stove in extracting as much heat as possible. I've thought of closing the damper all the way, but as of yet haven't been "brave" enuff.

Be careful about the assumption you gain more heat with a heat exchanger wrapped around the firebox (combustion chamber), These features sound wonderful and are in fact great marketing tools. What kind of stove do you have, can you post some pics? If you have a blower on this heat exchanger its a potential double whammy because it could cool the firebox to such a degree it affects combustion (and it definitely will NOT produce more "heat" to the inside of the home). With hand fired coal stoves the key is all about radiant heat and things which help extract more "heat" into your home are obtaining the least insulation factors in firebrick and body of stove (without compromising its safety and quality), baffles inside the stove to direct exhaust gases, manual or baro dampers to help slow draft to the minimal necessary, etc. its a fine line for sure that many manufactures worked years trying to perfect. Typically ceiling fans or doorway fans are a much better way to go.

Example of one way stove manufacturers can extract more heat into your home is using hand poured firebrick that molds to the stoves combustion chamber and/or building the combustion chamber or firepot with heavy duty cast iron/steel allows for much thinner firebrick (allows heat to "radiate" into the home far better). When a coal stove uses big thick prefabbed firebrick its cheaper and easier for the manufacturer and certainly case can be made that replacing and buying replacement firebrick is simple (but this keeps the heat inside the stove and up the chimney). All stoves are NOT equal (no matter what their BTU output states) and those who have used many different stoves and models over a long period of time know this to be true.

end rant about the myths applied to heat exchangers I hope it helps some people understand better about some of the design concepts vs marketing plan of some stove company's

He has a Franco Belge 10-475. The heat exchanger I believe he is referring to is this stove has flue gas exits at each end of the narrow rectangular fire box. It then has a rectangular cast iron channel in bolted together sections around the side of the stove, across the back and into the T shape that then exits the stove all under the sheet metal skin. I guess you could say that the rectangular flue pipes are heat exchangers because they extend the flue gas travel around the sides, around the back and then out. I had one.

It would burn just about anything with a BTU value and was a good stove so long as you accept it's limitations in the BTU ranges and don't overfire the puppy. They are a safe stove and virtually impossible to make them have a coal gas boom. My wife was going to tend our stove when I wasn't home and I wanted no surprises. I did everything your not supposed to do with a coal stove on purpose and the best I could do was fill up the firebox with what looked like boiling blue flames that went out within a few seconds.

Rev. Larry

The stove in question is a Surdiac 513 which is the smaller of the two sizes in the Gothic series.

The heat exchanger is a large chamber at the rear of the stove.

Be careful about the assumption you gain more heat with a heat exchanger wrapped around the firebox (combustion chamber), These features sound wonderful and are in fact great marketing tools. [/quote]

The Surdiacs have a sheetmetal chamber that ducts the heat from the firebox through a couple portholes up high on either side of the stove externally. It's mounted to the rear of the stove and is almost as large as the entire back of the stove. The stovepipe exits from the rear of this box. So not only are you extracting heat from the cast iron firebox, but also the heat exchanger is radiating heat. Sort of like a black pipe radiates heat in your room,(only larger), if you're fortunate enuff to have this. (mine exits directly thru the wall behind it.)
My complaint isn't that the stove isn't making good heat, but doesn't have long burn times, due to clogging grates. I've been contemplating a baro damper next season, because most people with this stove seem to say they work better. I'm not 100% sold on the idea, because the stove runs well when the grates are clean. and I seem to have some luck closing down the MPD, and the intake damper, when I want to "fine tune" it at times. I know the baro is adjusted for draft, but don't know if it's adjustable to do what the MPD can do.

Well I believe I gave a very good description of the wrong stove. Normal for me.

Rev. Larry

blrman07 wrote:Well I believe I gave a very good description of the wrong stove. Normal for me.

Rev. Larry

I agree, it was a spot on description of a Franco Belge. Most of it though would also apply to the Surdiac.

franco b wrote:They stop excess draft which in a manual air intake stove can cause the stove to burn hotter than wanted raising stack temp. With your stove the thermostat will sense the hotter stove and close down the air.

The Surdiacs thermocouple will allow the intake damper to run the temps it's set at. If you want more heat, increase the thermostat knob to a higher setting, and it'll allow more air into the stove, and vice versa. Last season, with no exhaust damper at all, when I set the thermostat to a slower burn, I still had a very hot fire. Seemed like the draft, even on low settings was causing the temps to run somewhat high. I will admit the knob on the stove wasn't hooked up last season, and I was manually twisting the cable "by eye", and quite possibly wasn't setting it correctly. This season, I installed the thermostat knob properly, "and" installed an MPD. So comparing last season to this one, isn't 100% accurate.
Which brings me back to my original question. FB, you state the baros stop excessive draft, however is there a benefit to slowing the draft down in an attempt to retain more heat in the house? Or by installing a baro, my intake damper will be more effective in controlling the stove out-put, and don't even worry about choking down the draft? (like I can with the MPD)