Sand under Firebrick?

[SmellsLikeSyrupNH]

Hi all,
More questions from me today....

If I want to reduce the space between the bottom of my preheater pan base to keep the heat closer to the bottom of my actual preheater pan, can I line the bottom 1st with just the generic playground sand and place fire brick on top of that? I know it will add weight, but will that work? Right now the "tub" has some 1" blanket in it, and a few fire brick below the opening for the stack at the far end of the rig. Im thinking if I filled it all in with sand, then laid brick it will reduce the volume of the tub, and focus the heat more up onto the preheater pan...right now its about 6-7" of empty space between the bottom of the tub to the bottom of the pan.

Not sure if these pictures help with what im thinking....
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Basically I just want to reduce the space in the box to keep the heat focused on the bottom of the pan.....will sand help me accomplish that with brick laid on top of it?

[tuckermtn]

use vermiculite that you can get at most masonry supply stores in big bags. sand can collect moisture in the off season and help speed the decay of the sheet metal.

[SmellsLikeSyrupNH]

The vermiculite is heat resistant?

am I going to gain better heat transfer by reducing the space between the bottom of my tub to the bottom of the pan? I think physics tells me yes, but im not a physicist lol

Thanks Eric!

[Big_Eddy]

I'd want my base layer of bricks to be supported directly on the arch, not on a layer of sand. Why not just rest another layer of bricks on top of the base layer to fill in the space. Full bricks, half bricks, or full bricks on edge. That way you can tweak and adjust as you want. Doesn't have to be a full layer, just a few bricks at the appropriate point to force the flames up close to the fan bottom.

[mellondome]

The back of my arch is vamiculite with nlanket laying on it. No brick in that section. The orebious owner just used sand no brick

[tcross]

how close do should the pan be from the brick in the back of the arch? Sorry... don't mean to highjack your thread! When I made my arch i left about 5"... i know it'll do the trick cuz it worked when i test boiled, but if it was closer together would that work better?

[SmellsLikeSyrupNH]

Thats my question as well, if i make that space smaller, will the heat intensify near the pan? Still havent found my answer really but im curious if it will work...that back pan i never expect to get up to boiling, although it would be nice, but it was close to 200 degrees on sunday and certianly helps as its filling the front pan...

[maple flats]

Vermiculite is heat resistant to far hotter than the arch will get. I found the best place to buy it was a commercial greenhouse supply, such as Griffin supply (formerly Malikowski). They will have it in 4 and 6 CF bags for like $20.00. If you buy it in small retail bags from Lowes or such you would pay about 10 times that much for the amount needed. You should leave no more than 1/2" under the flues, I only have 1/4" space. That forces the heat up into the flues, then at about 5" before the back of the pan, have a wall and drop down for the smoke to pass and then go up the stack.

[Big_Eddy]

My Rules of thumb

Calculate the cross sectional area of the smoke stack
For a forced air system, minimum area under the pan ~equal to the smoke stack
For a natural draft system, minimum area under the pan 1.5x area of the smoke stack.

Wide and narrow is less efficient than a round hole, so add a bit more spacea if your arch is extra wide.

[eustis22]

Area or Volume of the stack?

[OCHTO]

You could use wood ash. You'll have a lot of that. Its lightweight.

[waterfowlah]

Its funny you say that, I used wood ash to help fill in around some of My bricks.