How much space under pans?

[AndrewsofBow]

I'm on my 2nd season with my homemade arch and I'm still fine tuning. How much air space should be under the pans to the tops of the bricks? I'm currently at about an inch.

[NY mapler]

I have heard 2 inches is a good target. I have 3 inches under my pan. I just finished making the evaporator and have only tested with water so far, but it seemed to work great. With 1 inch you might get better heat transfer to your pans. You have gone two seasons with the 1 inch gap?

[AndrewsofBow]

No, Last year I started out with a bit more, probably 2" or so but over the summer I had a discussion with someone way wiser than me that's been in the business for a long time and he suggested an inch or so. I put everything together yesterday and did a quick boil of water, not a big fire and it seemed to work well. My only concern is with the blower if I'm over forcing too much air thru that space. If I was smart enough I'm sure there's a way to equate the Flu size 8" with the air gap underneath to figure out an ideal situation.

[Millsy]

This is my first year on my Oil Tank arch. The first two boils I had 2" of insulation leaving a 1" air gap under my pan and wasn't impressed with the boil. I removed 1 " of insulation to give me a 2" air gap and today it preformed much better. I also only have 6" stack.

[Super Sapper]

An 8 inch stack has 50 square inches of opening, so with a 2 foot wide evaporator you will need a tad over 2 inches under the pan to equal that.

[SSS2017]

Just the thread I was looking for! Good stuff here so far. I just picked up my 275 tank this past weekend and my neighbor will start welding on it this weekend. So 2" flat, or on an angle towards the flu? And I was questioning an 8" stack or 6"? I'd like to do 6" because I have on sitting here from a 55 gallon kit.

I met up this weekend with a local here who makes syrup and he had a professional evaporator and his had a 6" flu. I was amazed how quick his got up to boil.

[NY mapler]

[QUOTE=SSS2017;322049]So 2" flat, or on an angle towards the flu? And I was questioning an 8" stack or 6"? I'd like to do 6" because I have on sitting here from a 55 gallon kit.

I went with 8" stack on my oil tank and I was getting a great draft through with it. I forget the math behind figuring out square inches of your stack vs the space under your pan, but for a 4' x 2' quite a few people on here were recommending a 8" stack.

As for the angle towards the flu, I went straight up after the fire box for a couple reasons. It was going to be easier to build it straight up and easier laying the fire bricks. And I asked the same question in a thread a while back and a lot of guys said with a smaller pan (4'x2') I would want to go straight up so the hot gases would have the most contact with the pan. Hopefully that makes sense

[NY mapler]

http://mapletrader.com/community/showthread.php?29557-Pan-height-and-arch-design


This might help to explain it better.