Barometric Dampers and Cold Air Infiltration

 
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Ky Speedracer
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Post by Ky Speedracer » Mon. Feb. 23, 2015 8:09 pm

Okay, let me throw this at you and see what you think -
Let me preface this with two things, 1) I'm burning bit 2) I have freakishly high draft.

I come home tonight (5:30ish) and load in about 70lbs of bit. It's 19 degrees outside. Very little wind.
After loading, I leave both the load door and the ash door open for about 5 to maybe sometimes 10 minutes to get her going. My mano climbs to -.55. No kidding...I even pulled the hose off and zeroed it out and put it back on to be sure. The baro is pinned open.
Over the next 45 minutes, I end up with the primary almost shut, a quarter turn out on the spinner. The secondary is open to burn off the volitales. The over the door temp regulates at about 745*. The flue temp goes up to 300* but comes back down and settles in at 225* once the primary is closed down.
It will burn like this for a couple of hours slowly losing temp. By 9 it will be down around 480* and I'll open the primary a couple of turns. Midnight 400*. By 6am it will be 300*ish.

I took a lighter and lit a piece of paper and blew it out to get it smoking and then held that all around the stove looking for any leaks. Nothing. I did find that underneath the basement entrance door which comes from a sun porch area had quite a bit of draft pulling underneath it. This should be considered air from "outside" as the porch is not air tight at all and has no duct work supplying it.

I guess what I find interesting is that with such high mano readings I would think all that combustion air would drive both the firebox temp AND the flue temp way way up. The firebox is hot...750+*. But the flue pipe is 225* to 230*. I don't consider that all that high.

I assume the baro is doing it's job keeping the coal bed and firebox from over firing?
The fire box temp I assume is a product of bit coal?
My last assumption is that the air coming in under the basement door is make-up air...but is it going into the stove or the baro???

FWIW, my mano reading is taken about 16" from the breach in an 8" pipe...about 6" before the baro.
There is a lot of rambling above sorry. The questions and assumptions may be rhetorical as much as anything...


 
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Post by warminmn » Mon. Feb. 23, 2015 10:52 pm

If my house is 75 and Im burning LP in a vented chimney, isnt there going to be just as much air infiltration as if Im burning coal at 75, with or without a baro? Theres going to be just about the same amount of air leaving either way isnt there?

I guess it just seems like it would be the same air coming in whether its going thru my coal bed or thru my baro.

I do agree about the warmer my home is that more air is going to come in.

I think I'll go watch TV before I get a headache reading all of this. :lol: We need a scientist on the board :lol:

 
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Post by Lightning » Tue. Feb. 24, 2015 3:24 am

Ky Speedracer wrote:My mano climbs to -.55. No kidding...I even pulled the hose off and zeroed it out and put it back on to be sure.
Wow, that is incredible draft.
Ky Speedracer wrote:My last assumption is that the air coming in under the basement door is make-up air...but is it going into the stove or the baro???
Most of that draft is just natural cold air infiltration that would happen regardless of the stove and baro being used. A part of it is also make up air for the stove and baro..
Ky Speedracer wrote:I assume the baro is doing it's job keeping the coal bed and firebox from over firing?
It's gotta be helping.. :lol:
Last edited by Lightning on Tue. Feb. 24, 2015 4:19 pm, edited 1 time in total.

 
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Post by northernmainecoal » Tue. Feb. 24, 2015 9:10 am

Lightning wrote:
northernmainecoal wrote:Does a baro really change the amount of air infiltration at all? Assuming there isn't a mpd, and no baro I'm getting -.01 of WC. All of that air is passing through the firebed and out the chimney. With a baro set at .05 half of the air is being pulled through the fire bed. Is more than -.05 entering the baro?
If I'm interpreting your question right, you are wondering about air volume displacement of a combustion air opening with -.1 behind it compared to a baro AND combustion air volume displacement with both at -.05 behind them.

I believe that scenario #2 (the baro and combustion air opening with -.05) will move more volume of air out of the house and up the chimney. For the simple fact that the baro opening is so much bigger in relation to the combustion air opening.
I'm not sure that I follow....

With the addition of a baro the firebox draft is lowered but the draft in the chimney stays the same (in this scenario -.1). you're saying even though the draft is the same the volume of air passing into the chimney has increased due to the addition of a baro?

 
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Post by Lightning » Tue. Feb. 24, 2015 4:51 pm

northernmainecoal wrote:With the addition of a baro the firebox draft is lowered but the draft in the chimney stays the same (in this scenario -.1). you're saying even though the draft is the same the volume of air passing into the chimney has increased due to the addition of a baro?
Oh ok, I had to mull this over for a minute. I think about draft and pressure as being united in our application to coal stoves, although really they are different. Negative pressure in the system dictates the volume of air (draft?) that will be pulled into the stove and baro. But since it would be nearly impossible to measure the volume of air entering a stove or baro, we measure the next best thing, the motivator, which is pressure.

In my testing with the use of a baro on a natural drafting hand fed stove, pressure is nearly equal everywhere below the chimney. What I mean is, when I checked pressure at several points in the flue pipe, including above and below the baro, in the fire box and under the grates, the pressure readings were all within .005"wc during normal operation.. it makes sense to me that the pressure would be equal in the chimney also but would grow weaker as it was checked up higher until the neutral pressure plane in the chimney was approached where it would be zero (which should be the top). I would expect this to be true with most natural drafting hand fed stoves unless there are other dampers in the mix like MPDs or check dampers or any other restriction somewhere along the flue gas pathway.

That's my best stab at it..
I'm really not quite sure if the above helped or complicated things.. :lol:
Wait till Fred gets a load a that... :woot:

 
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Post by northernmainecoal » Wed. Feb. 25, 2015 6:56 am

I think about draft and pressure as being united in our application to coal stoves, although really they are different. Negative pressure in the system dictates the volume of air (draft?) that will be pulled into the stove and baro. But since it would be nearly impossible to measure the volume of air entering a stove or baro, we measure the next best thing, the motivator, which is pressure.
As you say, negative pressure dictates the volume of air that will be pulled. I think we all? agree that you cannot increase draft. So in my mind adding a baro will not increase the volume of air pulled from the house into the chimney it simply redirects a portion of it. If it did increase the amount of air pulled from the house, you could also say that adding a baro increases draft??

You lost me with the neutral plane in chimbly, 0 WC at the top of it?? how do the gasses get out??

 
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Post by hotblast1357 » Wed. Feb. 25, 2015 7:56 am

Ok now what about this curve ball.. I have a fresh air pipe 1/1/2 next to my furnace, that is bringing in fresh air, for my stove and baro to use. It is about 3 feet away from both inlets, and yes cold air is coming in constantly.


 
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Post by michaelanthony » Wed. Feb. 25, 2015 8:17 am

hotblast1357 wrote:Ok now what about this curve ball.. I have a fresh air pipe 1/1/2 next to my furnace, that is bringing in fresh air, for my stove and baro to use. It is about 3 feet away from both inlets, and yes cold air is coming in constantly.
That's no curve ball I call that a good idea. Without that, air would try to make it's way in. I realized this a while ago when I took clothes out of the dryer. The dryer had finished it's cycle and shortly after I went to the basement to bring'em up...well I was surprised how cold they were, the cold air was being pulled in via the vent and when I went to check the vent ice had formed and stopped the vent from closing all the way. I cracked a window in the basement and it flows right to the stove along the floor.

After reading this thread I am curious if and when we zero a manometer during the heating season when stack effect of the home is great should the manometer be brought outside and out of the pressurized atmosphere of the home? :? Am I getting a false reading when I zero the manometer in the basement when it is below the neutral plane?

I would also think a proper chimney is strongest at the top, like sucking on a straw. The hotter, lighter gases are increasing the draft.
just some Wednesday pondering. :)

 
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Post by coalkirk » Wed. Feb. 25, 2015 8:23 am

You guys need to relax a little bit. We aren't heating with nuclear reactors here. :D This is just coal burning. All a baro does is reduce draft and keep it steady in high wind conditions when artificial draft can be induced in a chimney. So yes, a baro does reduce air infiltration as it is reducing the draft, cooling the flue gases, slowing down the velocity of air leaving the chimney and therefore reduces the amount of make up air that needs to be sucked into the house. But the amount of difference here are so tiny that its hardly worth all the anxiety and brain strain.

 
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Post by Lightning » Wed. Feb. 25, 2015 9:34 am

Yeah but this is my idea of some good ol science fun!

I can see your point of view that the total air being used between the stove and baro is shared. But let's consider what happens without the baro.

Without the baro, the negative pressure in the fire box would strengthen causing more air to come thru the primary. This would cause the fire to burn hotter and force us to close it some.

So the question becomes, is less air volume needed to get the heat output wanted from a stove with lower negative pressure using a baro and larger primary air opening OR is less air volume needed with a stove with higher negative pressure with a smaller primary opening.

My take is that the stove and baro will need more total air volume since the air going thru the baro isn't contributing to any combustion.

 
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Post by titleist1 » Wed. Feb. 25, 2015 9:39 am

Lightning wrote:Without the baro, the negative pressure in the fire box would strengthen causing more air to come thru the primary. This would cause the fire to burn hotter and force us to close it some.
Or would you have to leave the primary open that same amount to have the stove burn hotter than you'd really like because a lot of stove heat would be rushing up the chimney......

I'm getting more confusilated!!! :wacko:

:)

 
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Post by franco b » Wed. Feb. 25, 2015 9:41 am

michaelanthony wrote:After reading this thread I am curious if and when we zero a manometer during the heating season when stack effect of the home is great should the manometer be brought outside and out of the pressurized atmosphere of the home? Am I getting a false reading when I zero the manometer in the basement when it is below the neutral plane?
As long as both openings of the manometer are open to the room when zero is adjusted, then zero will be accurate and not change no matter where the manometer is placed, inside or out will read the same zero because whatever the pressure, even if different from inside it is pressing on both sides of the liquid. A manometer reads differences in pressure and not absolute pressure as a barometer does.
Last edited by franco b on Wed. Feb. 25, 2015 9:46 am, edited 1 time in total.

 
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Post by coalkirk » Wed. Feb. 25, 2015 9:42 am

OK I get it. But I'm still trying to figure out if I walked to school or carried a lunch? :lol:

 
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Post by Lightning » Wed. Feb. 25, 2015 11:21 am

coalkirk wrote:OK I get it. But I'm still trying to figure out if I walked to school or carried a lunch? :lol:
Just to elaborate on that and make it more friendly to understand, I've come up with this...

Lets say it takes 20 CFM entering the primary at -.08"wc to run a stove at 400 degrees.. Now add a baro and the pressure falls to -.04 and the baro is taking 10 CFM in.. Since the pressure weakened in the fire box, now only 10 CFM is coming thru the primary. Now the stove's temp is falling with the less amount of primary air so we open it to get the 20 CFM flowing thru it that we started with.

So now it's more simple to see the stove without the baro is only using 20 CFM to maintain 400 degrees while the stove with the baro is using 30 CFM.

I appreciate the challenges since it furthers my thought and understanding of everything that is going on with a furnace and chimney system along with all the dynamics of the structure its in. Thanks.. :)

I also want to get back to to some of the other posts here too, I will, but gotta run out the door at the moment.. :)

 
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Post by northernmainecoal » Wed. Feb. 25, 2015 11:30 am

Are you sure that when you opened your primary to increase CFM more the baro didn't starting taking in less?


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