How Barometric Dampers Function, Why use a Barometric Damper

coalkirk wrote:

Coalfire wrote:

coalkirk wrote: Manual and barometric dampers BOTH are draft limiting devices. They do the same thing but they accomplish it differently. A baro limits draft by allowing room air to be drawn in the vent pipe. A manual damper limits draft by partially blocking the vent pipe. Both limit draft.

Actually a mpd does not limit draft. A measure of draft is with a manometer, when you close your mpd your draft does not drop manometer stays the same. same number means same draft, what you did limit was the volume that could ecscape.

With a baro when you push the flap open more the number on the manometer does go down, a lower number means the drafts has been limited.


Eric

Over fire draft, not chimney draft.

I will have to get a piece of brakeline and I will fish it in my secondary air and check the draft right above the the fire and compare to my manometer reading for my stove pipe(where the sampling port is between the mpd and the stove)

I will get a piece of line at work tomorrow and let you know the results.


Eric

lsayre wrote:In Dave's

Daves not here.

Richard S. wrote:

lsayre wrote:In Dave's

Daves not here.

It's Dave, let me in, I got the stuff!

franco b wrote:
I agree. I see instant change in manometer when altering MPD position, even by a tiny increment.

You are correct stove is burning low now draft at -.05 mpd open when I close it fully draft goes down to -.03, I would see a very slight change this winter when draft is higher due to the colder temps and hotter stove. So I guess the results are not linear, that was what I based my thoughts on as the mpd not limiting draft. I do know when I close the damper though I insantly feel the stove put off more heat.


The science of burning coal.


Eric

At the same stove temp, is more air leaving the house when using a barometric damper than a manual damper? Or are both having the same volume exiting out the chimney top per unit of time?

Explaining a baro is easy.

It's just like drinking whiskey with a straw. Full draft. Very easy to pull the whiskey from the glass, into your mouth.


Poke a hole or 2 in the straw, and see how much your "draft" pulls the whiskey up. That's your baro. It just lessens the pull on the glass (stove).

coalkirk wrote:Neither damper will. Dampers are draft limiting devices only. They will never help to improve draft, only limit it if there is too much draft.

I understand that, but the question really is, if draft is really low, say .01 to .02, will closing a manual pipe damper do much to inhibit the draft further since the holes in it are probably enough to maintain that draft? If draft drops further then the baro would be better under those conditions since it will maintain full pipe area under those conditions where draft unexpectedly drops during the night where a partially closed MPD would not.

franco b wrote:

coalkirk wrote:Neither damper will. Dampers are draft limiting devices only. They will never help to improve draft, only limit it if there is too much draft.

I understand that, but the question really is, if draft is really low, say .01 to .02, will closing a manual pipe damper do much to inhibit the draft further since the holes in it are probably enough to maintain that draft? If draft drops further then the baro would be better under those conditions since it will maintain full pipe area under those conditions where draft unexpectedly drops during the night where a partially closed MPD would not.

I totally agree with your line of thought here, franco. Although, its possible that the 1/8 inch gap around the baro door could contribute a tiny amount of negative consequence to the overall performance of the chimney during these times of low draft conditions. Some people here have even recommended covering the baro with foil to resolve the door gap issue. My personal opinion is that the gap around the baro door contributes a negligible amount of negative impact on the chimney's draw. I think it would be difficult to measure.

Ctyankee wrote:At the same stove temp, is more air leaving the house when using a barometric damper than a manual damper? Or are both having the same volume exiting out the chimney top per unit of time?

A baro uses room air to regulate flue pressure, so the answer to the first question is yes. This extra air leaving the house is replaced by air infiltration from outside which could contribute to cooling the house too.. BUT the advantage is that the baro keeps a consistent pressure in the combustion chamber which keeps a consistent amount of air flow coming in the primary air controls to feed the fire which keeps a very steady heat output instead of a yo-yoing situation. My furnace will burn for 12 hours and longer and only vary a few degrees for the whole duration of the burn without being touched.

Rigar wrote:For the sake of any newbies reading this thread....someone should make it clear that this discussion pertains to HAND FIRED burning only.....?????

...if not...we will have to start a new thread !!

And this is what causes me to become irritated when people post based on assumption and not experience. I came here to research and learn and I depended on the integrity of the people that have hands on experience to share their knowledge.. Who do so willingly and unselfishly and I am forever grateful. I would hope that this integrity is preserved somewhat here so that others in the future searching for alternate ways of heating could also read and learn with confidence that people here have been doing it and know what they are talking about.. I'm sorry for being so rash, its really not in my character...

Doug [dcrane] attempted to put into written word what Larry Trainer of Chubby Stove fame showed and explained to Doug.
While the explanation using a tobacco-burning pipe was at times a bit difficult to follow, at no time did he claim that he
was expressing his own ideas about controlling draft.
Doug was repeating Larry Trainer's explanation.

So personal comments about Doug are not appropriate. He tried to share an explanation that made sense to him, when
Larry explained it to him, and Doug wanted to share..regardless of Doug's experience level, he was passing on
an explanation he heard from a well established and experienced coal burner and stove manufacturer.


Now: Smitty got it: a baro adds a vacuum relief port in the 'straw' to this glass of whisky..

I'll add that a MPD will pinch the straw mostly shut.

What Doug is saying is that an MPD holds heat in the stove by reducing exhaust flow rate, blocking the quick and easy
exit from the stove. If you open the MPD, the heat has an unrestricted exit path, so it heats the stove body less.

A baro reduces the maximum suction on the firebox. It does not put a restrction in the flu pipe.

Wrapping the mind around the MANY variations of draft and flow control of a stove's exhaust can definitely be confusing.
There are many problems with a single explanation, there are just too many variables..

With any explanation I would refer to Sting's byline: 'it depends'.

Greg L

Who cares about the baro thing....

the most important question to answer from this thread is why in the heck is smitty drinking whiskey through a straw??!!

I agree, Why and WHEN would Smitty drink through a straw??

Greg L

WOW

...this has been alot to take in !. Me thinks Larry Trainer may need to use a different type of smoking apparatus to illustrate to people how a carb works....uh..I meant "baro"

...but i do have one question:

Smitty- you really drink whiskey with a straw ???

LsFarm wrote:
The entire draft control and exhaust airflow control issue is badly misunderstood by many.

This is from the other old thread about baros and MPDs..... Greg sums it up nicely.... ... IN order to describe the physical dynamics of everything involved with the chimney, dampers (wheather it be MPD of a baro), the primary and secondary air controls, in depth and in a way that is easily understood - would probably be monumental task.

And to describe it in a way that everyone would agree on --- well thats just silly of me to even suggest