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View Full Version : Newbie Air Under Fire Advice Please!



DSKUP
02-17-2013, 12:17 PM
Howdy. I have a 2x4 evaporator with an ash door. The ash door has two 2.25" vent holes with sliding covers. The whole set-up is on the heavy side for the size, 1/4" plate steel and 16 GA stainless fluted and divided pan. I have 8' of 6" stove pipe for the stack and the unit is fire bricked and insulated. Last year was the maiden voyage for this unit, but we had no sap flow due to the strange weather. So no syrup, but I did try it out with water and had a hard time keeping it rolling strong, presumably due to the overall mass (especially the heavy gauge pan).

Therefore I want to experiment with air under fire. My thinking is that I would insert two 2.25" automotive exhaust pipes into the ash pan vent holes, with hose going to a blower box with a 250cfm squirrel cage, variable restriction on the air intake. I was thinking I would drill a bunch of holes on one side of each exhaust pipe (as to angle the air upward toward the grate) and cap off the pipe ends. This is a temporary deal just to try out the concept.

Does this sound like a viable plan? Any advice? As a more permanent solution, could I just duct the blower to the back of the fire box (but below the grate)? Would my pipes with drilled air outlets really do anything, or does pressurizing the box below the grate to have the same effect? I've heard of using baffles for AOF, but not AUF.

Lastly, can a standard blower (like a Dayton PSC or SP) be mounted directly on the firebox below the grate, or would that get too hot for the blower assembly? Is 250 CFM about right? I have a chance to get a 790cfm blower cheap, but it seems like it would be super loud and probably blow the coals out the stack.

I appreciate your time in responding and hope you have a great season!

adk1
02-17-2013, 01:24 PM
I would do it under the grates as your second statement illustrates to. Build a plenum for it. You can check out my photos page to see mine. I basically copied the Grimm woodsaver in the LEader catalog. With that cfm blower I dont think you would need to use that on max. I have a 365cfm blower for my 2x6 which is plenty. I also purchased a rheostat for it so that I can adjust it..works perfect.

DSKUP
02-17-2013, 01:48 PM
Thanks for the reply. When you say it's more than enough CFM, are you referrring to the 250, or the 790? I'm also looking at a 270cfm blower, Dayton 1TDR3. Could you tell me the make and model of your blower? I will take a look at your pics, thanks.

adk1
02-17-2013, 01:51 PM
Well, hard to say. the 250 CFM blower would probably work on the 2x4 but if you were to put a rheostat on the larger one that would give you more options to see what cfm works best..also, you will be able to reuse the blower when you get a larger evap..which you will.