Exhaust fan for small shop

[Dale Critchlow]

I plan to install an exhaust fan in my new 14' x 24' shop. How large a fan do I need? I have a cyclone and mostly need it to exhaust the very fine dust, the hot air during the summer and the fumes when doing finishing.

I can get a variable speed 1/15 hp Dayton 18" unit with a flow rate of 850CFM at 0.125" of static presssure for about $225. Automatic shutters are included.

Their next largest unit is 1/4 hp 20" unit with 2245CFM at about $350 with the speed control. This is getting rather expensive.

I am interested in hearing what others do.

Dale Critchlow

[Rob Russell]

I plan to install an exhaust fan in my new 14' x 24' shop. How large a fan do I need? I have a cyclone and mostly need it to exhaust the very fine dust, the hot air during the summer and the fumes when doing finishing.

I can get a variable speed 1/15 hp Dayton 18" unit with a flow rate of 850CFM at 0.125" of static presssure for about $225. Automatic shutters are included.



Assuming adequate venting to provide replacement air, if your shop has 10' ceilings the smaller fan will change the air in the shop 15 times/hour. That seems fine to me, considering that the OSHA standard for laboratory air exchanges is 12 times/hour.

A couple of questions, though:


What is your source of replacement air - an open door? How will that help exhaust hot air in the summertime?
You're planning to use this as a fan to exhaust finishing fumes. Vermont can get pretty sticky. I'd think you want to be careful about a powerful fan exhausting air and sucking in humid air to a freshly finished piece. If your plan is to have air-conditioning in the shop (doesn't sound like it), is the HVAC system powerful enough to keep up with the exhaust fan?
Is your finishing area close to the exhaust fan (so the fumes aren't pulled through the shop)?
Lastly, if you're running this in a shop with a furnace/boiler or wood stove,beware that the fan will suck whatever is in your chimney right back into the shop.


Just some thoughts.

Rob

[Scott Coffelt]

Not that this isn't normal, but if you have a cyclone why are you still getting fine dust? I have two Torit filters on my system and the only way I see fine dust is if I do something not attached through the cyclone. I have not made a down draft table yet, so when I sand I do get some fine dust. I plan on getting a Fein one of these days to help with removing dust on project too large to fit the DD table.

Anyways, if your system is designed and working correctly, you should be capturing all fine dust. I have thought about installing a bathroom exhaust fan venting out through a dryer vent to expell odors from painting and staining, but would not see any other real advantage.

Just curious.

[Tom Pritchard]

Scott, I feel that you may be looking at a fan that will be pulling more air out of your shop than necessary. I would also worry about how all that fine dust would affect your fan motor. A while back, I saw a homemade plan for a small squirrel cage fan that was enclosed in a plywood box (like an exhaust hood), and the bottom of the box held a 20"x25" furnace filter that trapped dust before it made it into the fan motor inside the box, or into the exhaust ductwork. The fan exhausted through a 4" pipe to a dryer type flapper on the outside of the house. It kept the shop slightly negatively pressured, and got rid of the fumes before they made it through the house. Some fans are even variable speed so that you could adjust the speed to fit your needs. Just a thought! Good luck!

[Dale Critchlow]

Thanks guys for the comments!

Rob: One reason I wanted a fan is to exhaust the hot air when I first open the shop. It gets pretty hot when the sun beams down on for a few hours with the door closed. I can open two doors and three awning windows in the summer so the hot air can be moved out pretty quickly. Also, there are times, for example, routing without a router table, which fills the shop with dust very quickly. A fan can more this out relatively quickly. I also have a air filtration system but it takes it much longer to clear the air.

I tend to do the finish work in the fall and spring when I can get ventilation without it being too cold or hot. Therefore, I can use a variable speed fan to move the fumes out. The shop has a vaulted ceiling with the fan about 10 feet from the floor. I don't think this will affect the finish work.

Scott: I also have two Torit filters on my 1 1/2 hp cyclone. It doesn't get all the dust from the sawing, routing and sanding. Perhaps, a larger blower on the cyclone would help. I found that, in the summer in my old shop, sitting a portable fan in one of the two doors greatly reduced the feeling of being dusty.

Tom: I have used a small exhaust fan with two 4" ducts for several years in the shop. It is great in cold weather when you want a little fresh air to help clear out the dust after an operation where the dust collector doesn't work well. It adds a little to the heating bill, but I decided my health and comfort were worth a little higher heating cost.

In any case, I bought the variable speed 1/15 hp fan today and installed it. It seems to work fine. I am about to put the insulation on the vaulted ceiling and it gets really hot up there when the sun is beating down on the roof!

Thanks,

Dale