Stack damper needed ?

[shiirooms]

Entering my second season using a Sunrise Metals evaporator with 2x3 divided pan. Last year I had to maintain a stack temp of +1000 deg to maintain a hard boil. My stack is 12 ft high and 6in. dia. straight off the top of the evaporator. Sunrise has a fairly large/long fire box and it seems a lot of heat is being lost up the stack and not retained under the pan. Question is -- would putting a hand operated damper in the stack at possibly 18in. up make any improvement in controlling heat loss ? and improve the boil ? It may be possible my temp are lower since I'm using a $15 wood stove type thermometer. Any advise would be appreciated.
Dave B

[psparr]

How much room do you have under the pans? You probably need to restrict the space below the rear pan.

[maple flats]

How much room do you have under the pans? You probably need to restrict the space below the rear pan.
As psparr suggests, you likely are not forcing the heat up to the pan enough. You want the restriction under the pan. On a bigger set up it is usually done under the flues either raised or drop. When I had a half pint (2x3 flat pan) it was just a firebrick wall in a short ways from the rear smoke outlet. That had a 6" stack and I think the space between the pan bottom and the brick wall top was about 1.25-1.5", then behind that it was straight down to where the stack exited. On that your arch it sounds like the stack leaves the more like bigger arches, (out the top, behind the pan(s)). For that I'd say the brick wall will go to the bottom of the arch and then a layer of flat bricks on the floor of the arch behind the brick wall.
Is your's designed like this?

[Bucket Head]

Dave,

I've "been there, done that", and it does'nt work like you'd think. I thought it would too. It actually does more to restrict your draft, slowing down your fire, than it does to increase heat in the arch.

I agree with the others. I played around, changed, installed, removed, installed again, etc. my fire bricks until i got the heat where it was supposed to be. Sometimes it takes experimentation, but you'll find a set-up that really increases (and maintains) a boil. My original rig was a 2x6 with flat pans, but thats not too different from your set-up.

And I never touched the damper again. It remained open while I owned it and I removed it from the stack when I sold it. I did'nt want the new owner wasting his time with it!

Steve

[shiirooms]

As Maple Flats asked this evap is similar to the bigger ones. It is commercially made thus I had no control over the design. The fire box is +22in long meeting a bricked fire wall one brick height then the raised floor extending to the stack etc. The air space between this floor and pan is a strong 6 in maybe more. If I understand the drift of the thread so far, I should alter the fire box design by either adding brick to raise the floor and get the fire to within 3in of the pan. Possibly shorten the fire box also. Otherwise add a baffle infront of the stack hole to force the heat up and then around the plate before exiting out the stack.
Dave B

[Super Sapper]

You want the open area under your pan after the ramp to equal a little more than the area of your stack. At the top of your ramp or wall you want to come to about 1 and 1/2 inches from the bottom of your pan and keep this distance from the pan all the way back to your stack base. You can use ceramic blanket or vermiculite to fill in this area bricks are not needed here. You may still get a high temp. out your stack but you will be getting the most out of your heat.

[psparr]

You want the open area under your pan after the ramp to equal a little more than the area of your stack. At the top of your ramp or wall you want to come to about 1 and 1/2 inches from the bottom of your pan and keep this distance from the pan all the way back to your stack base. You can use ceramic blanket or vermiculite to fill in this area bricks are not needed here. You may still get a high temp. out your stack but you will be getting the most out of your heat.

Good advice. Don't make your firebox smaller, add more wood. Like super sapper said reduce height just after the firebox. Seems as though your arch is set up for a flue pan. I guess most are? I'm homemade so not real sure. Also I feed cold sap and my back pan is tough to keep boiling good.