Building my kiln 18' long, 6' 6" wide. Time to mount the fans. The fans I have are Air King high velocity. 3 speed, 18", 3190, 2970,2660 cfm. I am thinking the most I need is 2 fans. Yes ? No? Thanks for any input. Tom
With those ratings you should be fine with two. I used 2 in mine and I get plenty of airflow through the stack.
That is the way I am leaning 2 fans. But after looking through old posts will 1 do it? Maybe mount 2 and set it up to run 1 or 2? I picked these up at auction for 5 bucks each and was not thinking maybe to high of cfm.
You can use lower volume fans when under 30% MC.
The basic formula for cfm is (sticker height (inches)/12) x lumber length (feet) x number of layers of lumber x 200 fpm .
Example. 3/4"/12 x 16. x 22 x 200 = .75/12 x 16 x 22 x 200 = 4400 cfm. Then add about 50% for leaks to get 6600 cfm for wood over 30% MC
I'm not familiar with these fans but I would be concerned about what temperature they can be run at. Most motors have a thermal overload that will shut them down usually around 104° F or 40° C.
I had not thought about thermal protection, will call Air king and ask. The other idea is a furnace fan, not a blade but cage fan. Will this work? Not sure of cfm but has to be high?
K-Guy, After looking further. The 140f or 40c is amb temp rating or temp in kiln. Plus class A is +55c so over 200f. That being said Air King was NO help, not meant for that. Would not tell me class of motor, A being lowest. My furnace blowers are all 40c class A. Hoping to put fans in today but may sleep on it. What say you all? Thinking no one is running better fans for heat than these other than the auto fans. Would the furnace fans (cage) be a better choice? Not sure of cfm but I have a matched set to try. Thanks
I said 104° F not 140° F. Big difference there.
A cage fan would be nice if you were plumbing with duct work. I think your fans will work based on the temp you stated that they can work under. The question may be that you are better with three to spread the air movement the length of the kiln, and based on Doc Genes calc. the two would barely make the min. requirement at full speed. you would manually turn up or down for diff. species and or load size. Esp if you already have these fans, I would shoot for the middle of what is needed so you can cranks things up or down a bit as needed.
Sorry K, I knew 40c = 104f. A typo on my part. Class A motors are good over 200f but not sure at what temp they will kick off. Thanks
Doc, I was not thinking of duck work. I have enough work in this already. Going to check into cfm on the cage blowers. Thanks
I agree, and I did not think you would, but that is the advantage of a cage fan like what goes in a forced air system. they are usually still on the cold air return side. if you already have 3 fans, I would use those and test to see where the motor shuts off temp wise. i.e. the motors on the squirrel cage fans may shut off at the same temp.
I went through a very similar process as you're doing now when I was choosing fans for the kiln. I ended up rescuing a couple blade fans that were used for venting a greenhouse and the worked out well. Don't know the original source, but they look like they came from grainger. Just a Dayton motor, blade, and cage. Too pricey to buy new from grainger, but more than adequate to handle the air flow AND the heat in the kiln. Point being, most of these fan motors seem to be ok with the environment. A lot of people buy cheap box fans and they do ok. I don't see how the box fans produce enough air flow, but a lot of people (like YH) are using them. Could be that the box fans from a few years ago are better than what I could find. ??
I think (I mean I guess) that a squirrel cage could work if you can make it fit. It may even be better. Squirrel cage fans tolerate static pressure better than a blade fan, and that is a factor when you use them in a kiln. The real goal with the kiln fans is to pressurize the plenum. It's not like sitting a fan next to a lumber stack. The pressure in the plenum is what produces the air flow through the stack. Same principle in a duct.
Hopefully that will help some, but at least it's more words. :D :D It pays to look around and figure out a good way to add fans without breaking the bank. When it's all done, measure the air flow as it comes out of the stack and see what you get. That's when you'll know you've won the war.
Mr. WoodDoc provided a good equation for calculating the result of a given CFM input. Static pressure figures into that CFM figure published for a fan because it decreases the actual CFM. Determining static pressure for a fan installed in a kiln isn't easy, or even possible (lack of data), but looking at the de-rating figures gives you a point of comparison. After all the analysis is done, just pick some fans and WING IT! But you're winging it with CONFIDENCE!
Good luck.
Thanks for the advice guys. I do not think the squirrel cage are high enough cfm, about 1k each. I think. So the fans are going in, if it rains tomorrow. Working in the garage and want to get it out to paint before roof goes on.