blower cfm

[Bentley Wood Maple]

How large a blower do need to look for to add air under the grates in a 3x8 raised flue? Where to look for one? Amazon has a 465 cfm blower for about 100$. Looks small...

[JeffB]

Blower size is based on stack size ...
Radius x 3.14 will give you square inch of area of stove pipe
Then mutiple the squared inches of pipe by 15cfm per square inches.
Example
8 inch pipe has a radius of 4 inches
4 x 3.14= 12.56 inches squared
12.56in x 15cfm per square inch =188cfm
15cfm per square inch is a good average to base your minimum blower size .
It's easier to throttle a blower back in cfm then it is to try and get more air after you install the wrong blower.
What size is your evaporator and pipe. I have a 2x4 evaporator with a 7 inch pipe I run a150cfm blower on a reostat and stack can hit 1200degrees if i wind it up.
Hope this helps !

[n8hutch]

I just used a large oil gun on my 2.5x8. , it works great and it was Free. I had a piece of plastic that coverd roughly half the opening before I put my airtight front on because it would blow ash out between the two doors. I think stack Temps are all relative to how far beyond the flue pan you are measuring, and the diameter of your stack. I run mine about 900° but my stack is thermometer is 5 feet from the back of my flue pan and I have a 12" stack. Works great for me. Before I added the blower it ran about 450-500

[Bernie/MA]

I took apart a microwave once that had a small blower in it. I use it to get my shop stove going.

[acafro]

I've got a 400cfm blower on my 2x4. I am very glad I oversized it. It's very easy to "choke" it down just by blocking an intake. And It's one less thing to worry about when I upgrade or add additional stack. Most of the season I ran it at about 1/2 volume. But certainly had time when it ran wide open. Just my opinion

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[acafro]

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[cfenton86]

[QUOTE=JeffB;311861]Blower size is based on stack size ...
Radius x 3.14 will give you square inch of area of stove pipe
Correction
Formula for area of a circle is πr²=A
It will throw off your calculations a bit if you don't square your radius

[Wizbi]

This thread caught my eye. A couple years ago, I decided to add blower intake to my outdoor pit. I assessed sources and quickly realized commercial blowers were out of my price range. I went to a local appliance dealer who had blowers from microwave over-range hoods parted out from trade-ins on the shelf and was willing to sell them to me for $5.00 each. These blower motors are a squirrel-cage type design and they move a lot of air. I had to make a simple box to house blower, but boy do they make an ideal hi/low speed blast-furnace blower. Keeps my sap at a rolling boil. One word of advice - also ask them to throw in the capacitor module that is part of the blower circuit. Appliance dealers have al lot of these also since they are a common failure item. It is quite likely they stored that part also since it is mated with the blower motor. Circuit diagram is normally glued onto blower motor housing.

Hope this helps.

[SmellsLikeSyrupNH]

I got a Dayton 1TDT2 blower on Ebay for my 2x6. This thing is a TANK of a blower, what I did was cut a circular piece of sheet metal and basically created a damper to cover the inlet. If I need more CFM I will open the piece more or if I feel its blowing too hard I close it up a bit. I was looking for a picture of it but I cant find one right now. I would suspect for a 3x8 this blower would be ideal for you, its probably a bit over powered for my 2x6 but I can adjust as needed.

Using that calculation above it says I need just a 149cfm blower.....well the one I purchased does 549cfm LOL so im not sure if that's the right calculation or not, but it works for me.

Good luck!