I really like the idea of an automated pipe damper but it takes away from the simplicity of most stoves by adding a level of electronics. A barometric damper bring run off of preheated air is very simple and would address the issue if it could be made to close in the event of a chimney fire.
Yes, your stove is over drafting... Blame the ...
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Essentially it is a barometric damper also, just a very different location and a much smaller air feed.
I strongly disagree, regardless of air pre-heating or not the intent of a BD is to reduce flue temps to reduce draft, on a tall chimney like mine (36ft) water vapor will be condensing at the top of the stack before the draft is brought back within specs.
If the air is preheated enough to prevent creosote it is also too hot to be effective in reducing stack temps, which means its ineffective in reducing draft.
No a bd is not meant to reduce draft by reducing flue temps. It reduces draft by introducing dilution air. This weakens the vacuum. Yes currently it also reduces the flue temps because the dilution air is cool. It would be just as effective with hot air
Maybe I am missing something. Is draft reduction in the chimney the goal? or draft reduction in the stove? With a barometric is the draft reduced in the chimney or just the stove? Wouldn't the barometric draw air from the room it is in maintaining pressure in the chimney just reducing pressure in the stove?
Then you are going to need a huge volume of dilution air to reduce vacuum. Essentially what that is doing is using the friction within the chimney to reduce draft due to high flow rates, on a 6" or 8" chimney those volumes are going to be many times the volume the stove generates in flue gases.
As an experiment of this I pulled the cleanout cap on the tee of my chimney to see how much air gets pulled in while burning, It's a lot, I wouldn't be surprised to find the volume of air being drawn in the opening to measure in the hundreds of CFM.
I already believe I put too much hard work into processing wood just to go up the flue in the form of hot gases, I'll have no part in deliberately sending more up the stack.
Reducing draft in the stove is all that's needed, of course reducing chimney draft has the same effect, but definitely isn't needed if you can reduce draft only on the stove.
Realistically you wouldn't even need to reduce draft on the stove, ideally there would be a mechanism to maintain constant airflow into the stove regardless of draft, then draft doesn't matter as long as there is enough to light the stove. That would be the holy-grail of stove control.
No not at all. When dealing with low draft a tiny gap in an area on a pipe joint can make .01" of difference in draft.
Highbeam
Minister of Fire
If the draft demand is satisfied by non firebox air then your hot firebox gasses aren’t being sucked out prematurely.That’s the point.
Outside air connection to your stove and/or barometric damper means you are not dumping conditioned air.
Finally, 36’ is ridiculous. I’m more concerned with a stove designed for a normal 12’ chimney when your install requires 20’. The stove should easily accommodate that normal range.
SpaceBus
Minister of Fire
Or you could just set the draft properly and then air input would be constant. And a small leak in a gasket wouldn't cause a big issue.
Yes, my SIL's house is two tall stories (10 ft ceilings) and a full standup attic. Basement to chimney top is probably over 40 ft and 30'+ from the first floor fireplace.
And pulling that tee cap reduced your draft on the stove to zero. Or close to it. You would be sending the same amount of heat up the stack regardless.
I understand that
draft between the baro and the chimney outlet would remain close to the original draft so when the temp in the flu drops due to the dissolution of hot gasses the overall draft will drop some. The reduction of draft through the stove is made up by draft through the baro damper this causing the draft between the baro and the chimney outlet to be close to original draft.
Yeah my old 2 story houses chimney was 38 from crock to top. That is why I had 2 key dampers.
But if you use outside air you cool the flue increasing creosote accumulation, if you use inside air you are wasting the valuable energy you spent heating with the stove in the first place, same goes for using preheated air from the stove as was mentioned a bunch of posts back.
I agree a 20' chimney shouldn't require any special treatment to work right, stoves should be built to accommodate this.
I agree, a flue damper does this well. But as is the topic of this thread, flue dampers are questionable under various codes and certifications. I know in the Province of Quebec they are not permitted at all.
Yes I know it reduces draft to essentially zero.
My point is a barometric damper on a chimney like mine will be allowing massive amounts of air into the chimney, either from outside causing a massive creosote buildup, or inside requiring more cold outside air to be heated to replace it, or robbing heat from the stove through a pre-heater as was proposed earlier.
Pulling air from inside or from a pre-heater is where the additional heat is being wasted up the flue.
But if you weren't robbing that heat to preheat the dilution air an equal ammout of air would be sucked up the chimney out of the stove. So no increased heat loss.
If you are running the same stack temp the heat loss would be the same
SpaceBus
Minister of Fire
The same amount of air will always be drawn up the flue. Under high draft situations more air is drawn in a shorter time and then it slows down later when draft reduces. There are only so many BTU in a load of wood and it needs the same amount of air if it burns fast or if it burns slow.
Depending on excess air in that flue gas. Stoves in an overdraft scenario have more excess air than a stove with the proper draft.
If you have 2 chimneys at the same temperature one with 25% excess air leaving the stove and one with 100%, the stove with 100% excess is loosing far more heat up the stack, which is the stove in overdraft conditions.
How much more? Does that small ammout of lost heat. Which honestly would only be a couple percent really justify the cost complexity and maintenance involved in adding electronically controlled damper or air intake? I don't think so at all.
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