Blower fan CFM

[adk1]

Looking to install a squirrel cage blower for AUF (Air Under Fire). Will be variable. What would be a good unit to get as for as CFM's?

[GramaCindy]

there is actually a formula for that info adk1….let's see if I can get this straight...(The blower size is based on stack size.

The formula to figure stack area is pi x radius squared, pi = 3.1416, so the area of my 7" stack worked out like this

3.1416 x 3.5 x 3.5 = 38.48 square inches

38.48 square inches x 3 cfm/square inch = 115.44 cfm's

[maple flats]

I had a 350 CFM blower for under fire air and had to damper the fan inlet about 75% when I had a 2x6. I think for under air you might want something in the 200 cfm category and damper or variable speed control it to regulate. A very simple way is to partially cover the air inlet to the fan, open and close as needed.

[RileySugarbush]

Agreed! 200 to 300 CFM will do you well on a 2x6 for under fire. Depending on your stack draw, you may need to make your arch airtight if blowing over 100 CFM. If you go all out and blow in 300 or more, your evaporation rate will be great, but your wood consumption will be huge. It's like driving around with your foot to the floorboard....You get there quick, but your milage suffers!

[adk1]

Interesting. So if I do go with the 180cfm blower I will be fine. IT will be on a rheostat

[SadSams]

Interesting. So if I do go with the 180cfm blower I will be fine. IT will be on a rheostat

I would get one closer to 300cfm. You can always throttle it down, you just can't get more out of a small cfm unit. I think mine is about 300cfm but do wish it was a bit bigger.

[wiam]

I have a blower from a Miller mobile home furnace. It is probably overkill but I run it with one side completely covered. I have about 10' of sparks coming out of the 10" stack. Rig has to be very tight or smoke will come out, but it boils like crazy.

[adk1]

my rig is not tight and I ahve a 7" stack

[Sugarmaker]

I would have guessed 250 cfm with a damper in the inlet to allow you to control the air flow. We have a 550 cfm on a 3 x 10 and it's plenty.
Regards,
Chris

[adk1]

I ordered a 265CFM unit and a rheostat that is made for running motors.

[Monster Maples]

I ordered a 265CFM unit and a rheostat that is made for running motors.
Did you make sure it is a shaded pole motor? If not the motor will burn it up pretty quickly.

[adk1]

nope, what does that mean "shaded pole motor". I saw one on Amazon.com. This is the rheostat that I got

http://www.amazon.com/SE-Electronic-Stepless-Speed-Controller/dp/B000HQAVNI/ref=sr_1_13?ie=UTF8&qid=1326547309&sr=8-13

and this is the blower

http://www.amazon.com/EcoPlus-Blower-265-CFM/dp/B002HJC5M8/ref=sr_1_3?ie=UTF8&qid=1326547361&sr=8-3

[RileySugarbush]

Shaded pole motors are low power single phase induction motors that don't need starter capacitors. Good for low torque apps like a low pressure blower. There is very little info on the amazon site, but that is most likely a shaded pole motor and will work fine with a triac speed controller. The controller you reference also doesn't have much of a description. Tt might be TRIAC but also might be a rheostat. For a small motor like that either should work, but the rheostat might get a little hot.

My guess is you will run full speed anyway. Just use a switch to turn it off for firing. If you need to adjust air flow, block the blower inlet with apiece of cardboard and a magnet.

[adk1]

well that is good info to know, thanks. I hope it works. Plan on installing it next weekend as soon as it gets here.

[RileySugarbush]

Be sure to report back!

[maple flats]

I have a blower from a Miller mobile home furnace. It is probably overkill but I run it with one side completely covered. I have about 10' of sparks coming out of the 10" stack. Rig has to be very tight or smoke will come out, but it boils like crazy.
Add AOF (air over fire) and you will get no sparks, they will completely burn up under the pans where you want the heat.

[adk1]

how do you create air over fire in an arch like mine???

[RileySugarbush]

how do you create air over fire in an arch like mine???

I welded up a separate manifold with nozzles and dropped it into my existing arch. You will need a much more powerful blower for AOF.

[wcproctor]

What happens with the ashes with a AUF blower? I just made one and I hope this works good.

[RileySugarbush]

What happens with the ashes with a AUF blower? I just made one and I hope this works good.
There will hardly be any ashes because there will be so much more oxygen for combustion. What doesn't get burned up will fly out the stack. You are likely to have a lot more sparks!

[Ecnerwal]

how do you create air over fire in an arch like mine???

Covered pretty well here, I think....

http://www.uvm.edu/~pmrc/Combustion.pdf

[wiam]

Add AOF (air over fire) and you will get no sparks, they will completely burn up under the pans where you want the heat.

Dave I tried that last year. Put too much time and money into it and could not make back pan boil. I do not know if it has something to do with the tube back pan.

[getting started]

Not sure if that is a big enough blower, I have a 540 cfm on my leader 2x6 and run it about 3/4 throttle all the time

[Kngowods]

I just made a barrel evaporator with steam table pans sitting down in it I had a trial run a week ago got about 4-5 gph was not very happy with that so I added a slope to the exhaust witch I have a pan sitting right in front of and put a squirl cage blower in the bung on the front door added 5 more ft to the chimney we were AMAZED the difference I don't think it will be hard to get better than 10gph 10gph will be easy. The blower I put on was given to me and much bigger than I wanted. how do you find the cfm?? It doesn't say on it I did damper it alot at first but wen I open it up half way it sounds like a torpedo heater!!!!

[adk1]

Hmm..How much stack do you have>? Well, if it isnt, I sell this one and buy a bigger one. For not even going have one the first year I think I will at least try it out

[wiam]

Any will be way better than none.