Baffle to stove top spacing

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Apr 5, 2014
I'm in the process of installing a secondary burn/baffle into a Grandpa Bear.

Do i size the space between the baffle and the top of the stove for the stove outlet size (8"), or the chimney size (6") I have a 6" insulated stainless liner that goes up a stone chimney inside my house. (It is not an external chimney)

If i space the baffle for the 6" liner that's 28.25 sq in. The stove interior measures 27.125 wide, so that is a 1" clearance between the baffle and stove top.

Sizing it for the 8" outlet (50.25 sq in) works out to a clearance of 1-7/8".

So which way do i size it?

Also im thinking about a roughly 2.5° slope for the baffle which is around 3/4" rise front to back.
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How high is the chimney to make sure you have strong enough draft first?

Size the opening for the chimney. A straight up top vent works reducing to 6, but adding more resistance for pipe configuration can reduce draft too much. You can always drop the baffle for allowing more heat out.

Make a cardboard template.
Set it on the rear brick retainers at rear.
Angle upward toward front to adjust space above baffle for square inch opening. Front of plate just ahead of lower bend in top. Using bricks on sides to support plate, you can lower it by sliding bricks fore and aft. It’s easy changing the template until you get what you want, then cut one from 5/16 steel plate.

You can start with the minimum if vent is straight up. Rear vent or horizontal pipe runs will require larger opening. Start more like 1 1/2, but you can always adjust it for exact draft.
Its a top vent stove.

Its about 30' from 1st floor to the top of the chimney.

I made the baffle per an idea from one of your threads. 2 pieces of plate with 1/2" square stock welded in between around the perimeter to make a plenum for the secondary air.

I am going to weld angle inside the stove to hold the baffle up. So i want to get it right the 1st time.
Ok, back to working on my stove.
I’ve got my baffle plenum welded up, and angle welded to the back of the stove to support it

so it’s looking like I will have a run of 32” (including the (2) 45 elbows), of 8“ stove pipe from the top of the stove to the start of my 6” stainless liner.

So I was thinking about setting up my baffle with a 1.5” gap between it and the top of the stove. And then use a key damper to adjust the draft lower if needed.
Since I’m welding in angle on the sides to support the baffle and create the slope, I’m reluctant to size the gap at 1” for a 6” chimney.

also is there a gauge or something else that I can use to adjust the damper for the best draft?
I always set baffle on adjustable supports and do not modify the stove.

I start with the minimum square inch opening and can always drop the front to open larger if needed. There are more factors than height and pipe configuration.

You should not need a flue damper to control draft while in operation. One is used for open door burning with screen in place if not his is a solid door stove.

Draft gauge at flue collar, Dwyer Mark II model 25 is fine, Magnahelic is easier to read. (and looks better if leaving it on the wall) You’re looking for .05 to .08, keeping it below .1 if needed with damper.