MPD Location

The whole concept implies that the stove is pushing its exhaust gases out into the flue, when in my mind its the chimney creating the negative pressure for them to go there. This is the deal breaker for me.

I'm not against trying it though. I've tried many things and have gotten unexpected results..

Seems like we would all be putting our mpd further downstream if there were significant gains to be had.. That's all I got haha..

I know that after reading that carb. comparison, I feel a need to raise mine a couple feet.

Aww dam it man. Do you know what this means?? It also is implying that the flue gases are moving faster behind the mpd than in front of it.. Oh no, my head hurts again..

Lightning wrote:The whole concept implies that the stove is pushing its exhaust gases out into the flue, when in my mind its the chimney creating the negative pressure for them to go there. This is the deal breaker for me.

I'm not against trying it though. I've tried many things and have gotten unexpected results..

Seems like we would all be putting our mpd further downstream if there were significant gains to be had.. That's all I got haha..

The stove can't push anything and the chimney can't create anything. It's just metal and/or brick and all they are doing is separating high pressure gases from low pressure gases to direct them out of the heated space. Plus, negative pressure is just a lack of pressure not some other type of force of it's own, so the lower pressure of the hotter flue gases in a chimney are being pushed by higher pressure outside the stove through the primary and secondary damper openings. The fire is just turning that higher pressure air into a much lighter, expanded gas by burning air and fuel.

All the force at work is the higher air pressure outside the stove (and the chimney) where the pressure is greater. If you could suddenly drop the air pressure outside a stove to equal that in the chimney what do you think would happen ? If there was a force inside the chimney the stove would keep going, but we know it won't.

It's like many mechanics think "vacuum" is something that sucks air and fuel into a motor when it's actually a "lack" of something. It's the pressure outside the motor trying to get into the low pressure area inside the cylinder during the intake stroke that does the work of moving air and fuel.

In other words, as a force for moving gases, suction sucks ! It can't handle the pressure !!!

Paul

"And, what about the Glenwood non-base heater back pipe option stoves that come with pipe, or without ? Their extra flue length is all outside the stove body. The pipe adds several feet of pipe length at least before the MPD. I don't remember hearing reports of it affecting how the stoves burn either way.

I doubt you'd be able to remove so much heat with a few extra feet of pipe that you'd see much difference in how well the stove burns, but you very likely will see a difference in room temp. "

Sunnyboy, there is a big difference in how a base heater with a suspended fire pot and an inner barrel pulling the exhaust gases completely around the firepot and underneath it and dumping it at the bottom of the back pipe. You get a more complete burn and much longer burn times and the ash comes out like a fine powder. A lot of the base heaters have that back pipe but have a mpd inside the top of the stove on the inside of the backpipe where, when shut, the exhaust is re-routed and dumps out at the bottom of the back pipe. The extra length of pipe isn't what's extracting the heat, the path through the inner barrel and around and under the fire pot is extracting the heat. You can hold the exhaust pipe BEFORE, NOT AFTER, the mpd and it's warm to the touch. changing the location of the mpd farther away from the stove doesn't extract the heat any differently, as it's a different process.

BPatrick wrote:"And, what about the Glenwood non-base heater back pipe option stoves that come with pipe, or without ? Their extra flue length is all outside the stove body. The pipe adds several feet of pipe length at least before the MPD. I don't remember hearing reports of it affecting how the stoves burn either way.

I doubt you'd be able to remove so much heat with a few extra feet of pipe that you'd see much difference in how well the stove burns, but you very likely will see a difference in room temp. "

Sunnyboy, there is a big difference in how a base heater with a suspended fire pot and an inner barrel pulling the exhaust gases completely around the firepot and underneath it and dumping it at the bottom of the back pipe. You get a more complete burn and much longer burn times and the ash comes out like a fine powder. A lot of the base heaters have that back pipe but have a mpd inside the top of the stove on the inside of the backpipe where, when shut, the exhaust is re-routed and dumps out at the bottom of the back pipe. The extra length of pipe isn't what's extracting the heat, the path through the inner barrel and around and under the fire pot is extracting the heat. You can hold the exhaust pipe BEFORE, NOT AFTER, the mpd and it's warm to the touch. changing the location of the mpd farther away from the stove doesn't extract the heat any differently, as it's a different process.

BP, yes, I'm aware of how the base heaters work and that they are very different. I said, "non-base heater option back pipe stoves".

I mentioned ranges and the back pipe stoves because with their not channeling flue gases around the firepot, they are more like what the OP wants to accomplish by moving the MPD down stream in the pipe. And, they don't suffer from too much heat loss because of the longer flue and pipe lengths before getting to the MPD.

With my range in indirect mode, the MPD is about 11 feet from the firebox. And, that's with a much smaller firebox and about 10-15% more stove heat radiating area then some of the bigger base burner or back pipe stoves have. It draws and heats fine.

This morning when I came down stairs, the pipe was 104 degrees on the stove side of the MPD and the top of the stove at the firebox end was in the mid 600 degrees with the primary's closed to a sliver, the MPD fully closed, but with the check damper open about 15-20%, . . . and it still had a mano reading of .01.

Paul

So what was the temp. on the stove side of the pipe? This isn't about a whole bunch of numbers & calculations, it's about--does putting the MPD 5,8,10 feet away from the stove body help in the distribution of HEAT--I think not on a coal burning device.

ddahlgren wrote:
Using that theory it would not help to add 4 inches in height to the stove to add more surface area.

How does raising the stove add surface area?

Read the last paragraph of Paul's post Fred.

I agree with Paul.

In my mind the ideal situation would be a chimney that completely radiates it's heat in the house to the point where the gasses exiting the flue are only hot enough to maintain a pressure drop across the coal bed sufficient to burn that coal.

A simple example would be a stove that is located in a basement with a stainless pipe that has a clear shot to the roof. It's entire length exposed to the inside of the house. Of course the MPD would be at the top of the flue, if it was even necessary.

I'd like to see a setup that uses a double wall stainless chimney pipe, where primary air is routed to the stove inlet via the entire length of the pipe. This would put lots of heat back into the appliance where it could radiate again.

Too much drift here now though!

coaledsweat wrote:

ddahlgren wrote:
Using that theory it would not help to add 4 inches in height to the stove to add more surface area.

How does raising the stove add surface area?

I think, he's talking about if one were to able to add 4 inches to the height of the stove body to increase it's heat radiating area. Not lift the stove higher off the floor.

Paul

freetown fred wrote:I know that after reading that carb. comparison, I feel a need to raise mine a couple feet.

S'matter, . . that hill your on doesn't give enough drainage for these type discussions ?

Paul

Ohhhhhh, discussion, never mind

Gekko wrote:Read the last paragraph of Paul's post Fred.

I agree with Paul.

In my mind the ideal situation would be a chimney that completely radiates it's heat in the house to the point where the gasses exiting the flue are only hot enough to maintain a pressure drop across the coal bed sufficient to burn that coal.

A simple example would be a stove that is located in a basement with a stainless pipe that has a clear shot to the roof. It's entire length exposed to the inside of the house. Of course the MPD would be at the top of the flue, if it was even necessary.

I'd like to see a setup that uses a double wall stainless chimney pipe, where primary air is routed to the stove inlet via the entire length of the pipe. This would put lots of heat back into the appliance where it could radiate again.

Too much drift here now though!

When I worked in a museum system I got to see a lot of old prints and photos left over from research for Bethpage Village, a recreation of life in the 1850's - 60's. One thing that was very common with the early cast iron stoves was the stove pipes had very long near horizontal runs compared to what you usually see today.

Quite often the pipes went the length of a room, or store, or church, at a shallow up angle before entering a chimney. Granted most were simple box wood stoves and small cook stoves, but they still wanted to extract as much heat from the wood they had to cut by hand.

Pictures in the archives from the later 1800's show the stove pipes getting much shorter, but the stoves were larger and better designed to extract heat at the stove. Now, many of the modern stoves look more like the early, simple box stoves. So maybe we need to go back to longer near-horizontal sections of pipe ????

Paul

My house built in 1874 was heated that way. I am the guy that fixed the pass through holes for the stack pipes. Looking at the pass through holes jn the walls. I am guessing a pot belly on every floor, The only reason I think those as when the house built it was the wrong side of the tracks.

Oh yeah absolutely... Longer pipes in the living space equals more surface area for heat transfer. I dig it.. But did they put their manual damper at the other end of the flue pipe?