filling under flu pan

[Moshers Maples]

I have a 2x6 raised flu evap. I have read about filling in the area under the flu pan with sand or vermiculite. How far back do you fill? How much of a gap is left between the end of the fill material and the base stack?

[psparr]

Should keep the gap close the whole way.

[Moshers Maples]

I am tight to the bottom of the flu's just not sure how close to the base stack to get. I was thinking the last 4" would be open, is that enough or would it restrict air flow up the stack?

[Brookside Maple]

I stopped where the base stack meets the evaporator and works great.

[MapleMike]

Hi
As a new owner of a drop flue pan, ( Leasder WSE 2x6 ) I'm trying to understand the concept here. Tell me if I have this right. The sand or vermiculite is placed on the brick and wants to reach the bottom of the dropped flue? Is this to protect it from burnout? Does it get in the way when cleaning between the flues or does that not happen that often.
Thanks for your help in advance, from a nervous new drop flue owner.
Mike

[maple maniac65]

I used 1 inch ceramic board then bricked. On top of the brick I ran 1 inch blanket under flues all the way from the ramp to the stack opening. It will increase stack temp though. Sides of my arch after 13 years are still like new no rust from excessive heat.

[maple flats]

My arch came with instructions. On my 3x8 Grimm raised flue there were sheet metal partitions across the arch. I think it was 2 or 3. I filled with vermiculite up to about 2.25" from the top of the arch. Then I laid a layer of full firebrick flat which are 2.25" thick. This settled the vermiculite about 1/4". Then I sprinkled a thin layer of dry refractory on the surface to mostly fill the cracks. Then I took a spray bottle that put out a fine mist of water and lightly misted the top, a few times.
The back partition (in fact all) leaned back slightly and it had a lip to give it strength on top that extended rearward 1.25". Behind that I stood up half bricks to support the lip and the weight. This left about 4" of the rear most flues exposed in the back. The rest of the back of the arch is bricked with half brick, sides and base. Once I started firing the arch slowly at first then gradually more intensely to cure the firebrick refractory, that moistened thin layer got hard on top of the flat bricks too. As it sets now, the space under my raised flues in about 3/8".
Those who use sand are adding a huge weight in sand, too much to depend on the belly of the arch to support it on a raised flue. Vermiculite weighs very little. At first I went to Lowes to try to get the vermiculite but that proved far too costly. If memory serves me (which it seldom does) it would have cost almost $750 at Lowes, buying the small bags they carry until I had enough to fill the space. Then I contacted a greenhouse supplier and they had it for just over $100, enough to do my arch (back in 2006), I bought 3 bags of fine, 6CF each for $39 each. In the end I had about 1/4 bag left. At the time it was Milikowski greenhouse supply, but they were later bought out by Griffin Greenhouse Supply. There are several outlets in the northeast US.
Here is a link to find the 12 Griffin locations: http://griffins.com/locations/index.asp

[Moshers Maples]

So this is what I did. Full brick on edge with half brick on its side covering the full brick and 1" ceramic blanket full width of arch an extending from the ramp to about 8" short of the base stack. The brick is spaced so it is enough to support the blanket without sagging. If I had gone full lenght of the flu pan I would of blocked base stack completely. This is less than 1/4" from the bottom of the flus. I used old brick and a 24"x36" piece of ceramic blanket, not much money spent. I had my first boil yesterday and had a hard boil about 3/4 the length of the flu pan and a decent boil the remainder. I didnt check to see if my evap rate was better, though it was making a lot of steam and seemed to go through the sap quickly.