understanding upper and lower draft controls and how they work

[David Wayne]

The manual for my brunco wood & coal stove says wood burns 80% as a gas 20% as a solid-more air on top.
And coal burns 20% as a gas & 80% as a solid-more air under the fire.

 

[TdiDave]

Fixed it for ya

Aaron, my Yukon has both under and over the fire air like yours. I suppose that you will get the best advice from someone who has the same model furnace, but for me, I find that leaving the fire have at least a small amount (1/2 to 1 turn?) of air from under (ash drawer) at all times gives a cleaner burn. I would think you would want to control the burn rate with the upper control more so. But like others have said, you'll hafta play with it to find the best results from your particular install.
Getting a manometer to check your draft makes it easier to set your flue damper for best results. I have bought (2) Dwyer Mark II (model 25) manometers now, off fleabay for $20 or less delivered to my door. I have mine mounted on the wall next to the furnace, hooked up all the time. As others have said, a baro will give you the smoothest most controlled draft, but a manual damper and a manometer are effective too. A lot of people will say heck with the manometer, but I like to be able to see for a fact what the wind and temperature are doing to my chimney and how my damper adjustments are affecting things, but I'm a tool hound too, so...

Question on the use of the manometer. I have burned coal for many years and have a manometer from then. I now have it installed in my wood stove. I had always tried to maintain 0.05 draft with the coal and that seems to be working good with wood as well. Question comes from I have to use the flue pipe damper to get the draft down to 0.05, but obviously the more restrictive I make the incoming air the higher the draft pulls. So if I understand correct I should get a good fire going that I am comfortable with (with flue pipe wide open the draft is over 0.1 at this point) then close it down to 0.05 tomkeepmthe heat in the room not up the flue?

 

[brenndatomu]

then close it down to 0.05 tomkeepmthe heat in the room not up the flue?

Well, I guess that is more or less what's going on. What you are doing is controlling how much air is going through your firebox, therefore controlling the rate of burn, and the velocity of the flue gasses through the stove/furnace. Controlling the velocity, or draft speed, controls the amount of time the hot gasses have in contact with the stove top or heat exchanger. This allows you to dial in for maximize heat transfer. Slower (lower draft) is better to a point, but after that point you are getting a smouldering burn and/or lowering the chimney temp too low...compromise...
-.05" WC is a pretty common standard.

You are checking the draft between the baro and the appliance, correct? If so, sounds like you have a pretty good handle on it otherwise.

 

[RMP]

Fixed it for ya

Aaron, my Yukon has both under and over the fire air like yours. I suppose that you will get the best advice from someone who has the same model furnace, but for me, I find that leaving the fire have at least a small amount (1/2 to 1 turn?) of air from under (ash drawer) at all times gives a cleaner burn. I would think you would want to control the burn rate with the upper control more so. But like others have said, you'll hafta play with it to find the best results from your particular install.
Getting a manometer to check your draft makes it easier to set your flue damper for best results. I have bought (2) Dwyer Mark II (model 25) manometers now, off fleabay for $20 or less delivered to my door. I have mine mounted on the wall next to the furnace, hooked up all the time. As others have said, a baro will give you the smoothest most controlled draft, but a manual damper and a manometer are effective too. A lot of people will say heck with the manometer, but I like to be able to see for a fact what the wind and temperature are doing to my chimney and how my damper adjustments are affecting things, but I'm a tool hound too, so...

Please tell me where the manometer is connected, and what pressure difference is good. I'm familiar with Dwyer products, but not this application. I suspect one line goes to the flue/chimney and the other to the body of the stove.
Ron

 

[jimdeere]

Open to the room the stove is in. Delta P or differential pressure is your draft.
Here’s a good read:
https://en.m.wikipedia.org/wiki/Draft_(boiler)

 

[RMP]

Open to the room the stove is in. Delta P or differential pressure is your draft.
Here’s a good read:
https://en.m.wikipedia.org/wiki/Draft_(boiler)

Thanks Jim, yes, that's a good article.
Can you please confirm the connection- the manometer has two ports. In your description, I gather one port simply goes to the room where the stove is installed; the Wiki article says the other port goes to the boiler (Stove, in this case). Are there guidelines for best diff pressure?

 

[brenndatomu]

Please tell me where the manometer is connected, and what pressure difference is good. I'm familiar with Dwyer products, but not this application. I suspect one line goes to the flue/chimney and the other to the body of the stove.
Ron

Sorry, just now seen this. Connect one line to the stove pipe, between the firebox and any pipe dampers, the other end to the right port (high) on the Dwyer. The other port/vent just gets left open to atmosphere.
The easiest way to connect into the pipe is to drill a 1/4" hole in the side, get a piece of flexible 1/4" copper tubing, a couple ft. long, bend it into a big S shape. it can then hang from the pipe...get a "1/4" compression to 1/8" FNPT" fitting to clamp on the other end of the copper, then a "1/8" MNPT to barb" fitting to go in the compression fitting...the hose attaches to that...

 

[RMP]

Thanks brenndatomu, that seems straightforward. Are there guidelines for optimal differential pressure?

 

[brenndatomu]

What are you running?
Most wood furnaces call for -0.04" WC to -0.06" WC...but some go as low as -0.03" WC, and some as high as -0.08" WC

 

[RMP]

Quote...What are you running?
Most wood furnaces call for -0.04" WC to -0.06" WC...but some go as low as -0.03" WC, and some as high as -0.08" WC - end quote

Ours is an old (35 years) Thelin-Thompson parlour stove - looks like an upright Franklin. They made two sizes; ours is the larger of the two.

 

[brenndatomu]

Quote...What are you running?
Most wood furnaces call for -0.04" WC to -0.06" WC...but some go as low as -0.03" WC, and some as high as -0.08" WC - end quote

Ours is an old (35 years) Thelin-Thompson parlour stove - looks like an upright Franklin. They made two sizes; ours is the larger of the two.

I have no clue on that one...I'd shoot for the -0.04 to -0.06 range then...unless you have a manual that shows draft specs...doubtful on something that old.

 

[RMP]

brenndatomu,
Thanks for all you help. If i get my manometer installed, I'll try to get back to this forum and comment on what differential pressure seems to work
Happy holidays,
Ron