Heat Physics

I have both dampers on my pipe. Never do I see any increase in heat when I close the manual damper. I use digital thermometers. Not even a single degree. I only see it fall. Which goes against the heat being retained idea because that isn't the case.

Just my view on it all. ..

I am with ya, that is how I would view it. But some are insistent in there perception. Even if you produce a scientific study, some will swear that their install, stove, chimney, house is different.

Kevin

I had the same view. I was completely found dumb when I closed the manual and saw the temp fall. How could that be??? I said out loud ... Then I hunted for explanation. Then the light came on and it all made sense haha ..

KLook wrote:Yeah, I can accept that Paul, I have seen plugged exhausts. Happens in chainsaws also with the build up in the muffler of exhaust port. Still, If it can't get out, it can't get in. It can't be magic. If a wide open MPD equals a *500 fire, then shutting it down will equal less then that. It make take a little time, but it will happen. Briefly, you may see a temp spike as the heat is prevented from flowing out the pipe, but very soon the fire will quite down and loose temp.

Kevin

I'm not talking "if", but "how much" ?

And yes, my little range will slow down with the MPD fully closed. But I'm not talking about the MPD being on, or off. I'm talking about matching the MPD to whatever the primary damper setting is that I happen to be using.

With the MPD partially closed to get the draft to it's sweet spot of .04, for whatever the primary is set to, it does run hotter and the stack runs cooler. Open the MPD fully and the stack gets hotter, but farther down stream within the stove (my range is a base heater in disguise) the oven and water tank jacket run cooler, but the plates over the fire box stay the same temps.

I was put onto the idea of testing to see if it has a draft/MPD sweet spot when I was trying to find ways to get the oven temps higher. I read some old kitchen range operating instructions and one of the recommendations is to use an MPD and partially close it. Guess what? It works. The oven gained about 25 degrees without having to do any changes in the primary damper setting.

If I turn the MPD down more than .04, the stack temps stay down, but the stove starts to slows down until it reaches the point where it will burn at that air/flue gas flow rate. Open the MPD more than .04, and the temps climb in the stack more than in the stove, again without changing the primary damper.

In other words, there's a fine line between where I can choke the stove just using the primary, but heat more easily goes up the stack, . . . and the point where, if I match the MPD to how much the stove is choked by the primary. By matching the MPD to the primary I don't choke the fire, but I do slow the exhaust gas flow. The heated gases stay on the stove side of the MPD longer. The result is, my temp tests show my stove's (I'm not saying all stoves) temps go up more than they will with the MPD wide open.

Each system is unique, so it doesn't surprise me that others may be getting different results.

Paul

Many many years of wood burning and hanging around even older wood burners taught me how they work. Both the solid and ones with holes in them. Close them down and let the smoke pour out in the middle of the night a couple of times because outside conditions change dramatically will educate you also. The baro just self adjusts to changes. NO brainah!

Kevin

Paul, I will say again. You must stand there with your hand on the MPD trying to adjust for that sweet spot. If you just put on a baro and adjust it for the sweet spot draft, you can walk away and have it right.

I have run more then one kind of kitchen range with wood and MPD's.

Lightning wrote:I had the same view. I was completely found dumb when I closed the manual and saw the temp fall. How could that be??? I said out loud ... Then I hunted for explanation. Then the light came on and it all made sense haha ..

Lee, Kevin, What you may be seeing.

Your larger stoves may be close to the maximum that whatever your stack system can flow, so that even a little restriction will have a bigger impact on how the stove reacts than my small kitchen range and it's 6 inch stack and tall, unlined brick chimney system.

Paul

KLook wrote:Many many years of wood burning and hanging around even older wood burners taught me how they work. Both the solid and ones with holes in them. Close them down and let the smoke pour out in the middle of the night a couple of times because outside conditions change dramatically will educate you also. The baro just self adjusts to changes. NO brainah!

Kevin

Paul, I will say again. You must stand there with your hand on the MPD trying to adjust for that sweet spot. If you just put on a baro and adjust it for the sweet spot draft, you can walk away and have it right.

I have run more then one kind of kitchen range with wood and MPD's.

There's a reason baros aren't used on old kitchen and parlor stoves. They don't work well for the low draft volume of the smaller fireboxes, coupled with long internal flues. The baro's leaky butterfly plates just become a check damper and they kill draft. And being small, with long internal passages, they aren't affected by wind and burn rate changes as much as your larger box stoves.

I can stand there for hours on end and watch the mano not budge at all, . . and I have !
Paul

I would agree with that statement if you turn the diverter over so that the exhaust goes around the oven. Otherwise, it is a pretty straight shot up the stovepipe.

Kevin

Straight up the pipe is only for starting and loading. At all other times, like base heaters, kitchen ranges are meant to always be used in indirect mode , or your just wasting a lot of heat and fuel.

Apples to oranges - you can't compare wood in a kitchen range to coal in the same range. They are two completely different animals ! So, you can't compare how controllable the draft is between the two.

Paul

pples to oranges - you can't compare wood in a kitchen range to coal in the same range. They are two completely different animals ! So, you can't compare how controllable the draft is between the two.

I disagree with that statement. They both are solid fuels affected by draft.

Kevin

And I burned coal in a kitchen range a little bet also.

Paul, I think the difference is that your cook stove has places for air to leak into it where our stove and furnace appliances are more air tight. This is why you want want to keep negative pressure in the fire box in check. A strong negative pressure in a leaky stove would rob heat out the chimney since the leaks add no benefit to combustion. This is the case where an increase in stove temp may be observed when the manual damper is closed. But like you said, there is a sweet spot or breaking point if you will, between negative pressure in the fire box, how far open the primary is and how far closed the manual damper is set with a stove that isn't air tight.

Not that I'm calling your stove leaky but that a stove or furnace appliance might probably be more air tight..

KLook wrote:

pples to oranges - you can't compare wood in a kitchen range to coal in the same range. They are two completely different animals ! So, you can't compare how controllable the draft is between the two.

I disagree with that statement. They both are solid fuels affected by draft.

Kevin

And I burned coal in a kitchen range a little bet also.

Magnesium is a solid fuel too, . . but the burn rate is a Bit@h !

Coal and wood burn so differently in a kitchen range that different dampers are needed to burn each well. For wood, very little primary, lots of secondary, and even in indirect mode, they need a check damper and an MPD to slow the burn rate down to useable levels. For coal, just the primary and the MPD is all that is needed. The small air gaps around the top plates are all the secondary air that's needed to keep the blue ladies dancing, and not get any puff backs, no mater how you load hard coal in it.

But, try using the same damper settings on a kitchen range that work best for coal, as works for wood, and get back to me about how well the coal burned. I've only got eight years using both, maybe I missed something ?

Paul

Lightning wrote:Not that I'm calling your stove leaky but that a stove or furnace appliance might probably be more air tight..

I resemble that remark, or at least my stove did. Now 3/4 of a tube of stove cement later, that's not a factor.

The difference the MPD makes is even slightly more noticeable now, because the stove is acting more like it was originally designed to.

Gotta go. Taking a weekend away. Stay warm.

I don't need a lesson from anyone in how to burn wood or coal in a kitchen range. Thanks. I understand what the dampers and such are for. We didnt get an oil appliance in our house until I was ten and wood and coal was the only thing keeping us warm in an uninsulated, ancient, single pane window, New England cape. It still remains that air flow is the key to burning either one. And consistent airflow is the best for both. Your MPD will not produce more heat from less airflow on any appliance you stick it on. Not as effectively and consistently as a baro. So if it makes you feel good, do it. But it is no more effective then having an airtight stove and restricting the air by how much you let in. You can only get heat from oxidation with requires AIR. Restrict it getting in or getting out, no difference.

Kevin