View Full Version : Barn exhaust fans - how big do I need?

Jun. 25, 2010, 09:37 AM
Our barn was not built as a barn - it was originally a workshop and was heated and cooled - thus no ridge vents and hotter than heck. It is also 'square' with a huge aisle and no doors north/south. Over the years it's been modified to try and facilitate ventilation, but it's still very, very hot. Just rollup doors on east/west, smaller openings north/south, several 3' square 'horse windows' and most of one side open from 4' up with an overhang to encourage ventilation. But the plus factor is it's connected to our house by a breezeway which is the best thing about it. Unfortunately, the house also blocks the south breeze for the most part.

We are buying 2 attic fans and having them installed in the eaves at each end. Our regular 'fix it' guy has found some commercial fans and my husband says with both of them, we should have a complete 'turnover' of air inside the barn every 10 minutes.

Is that enough to do any good? I am not sure. Our barn is about 1900 square feet -- probably close to 23000 cubic feet.

Jun. 25, 2010, 10:12 AM
Sounds about right. I have a similar issue with my barn...it gets HOT easy. Despite eave vents, a full ridge vent, cupola, 6 windows, etc. But I have a front aisle barn and one main door, so little to no cross breeze. And my barn area is in a valley type area so not much wind down there sometimes anyways.

I put in 2 16" vent fans, both are set into the roof and not the eaves though. They pull more air with my set up that way since they're pulling mostly from windows and one front 8x7' door. Eave set ups probably work better with a center aisle set up though, not sure.

My barn is 24x40...so 960 sf. My two fans do a full interior air exchange every 90 seconds - 2 minutes inside the barn. You can feel the breeze standing in front of the doors or windows. They're also shoving out all the hot air under the roof.

Are the fans you're looking at thermostat controlled? That's a huge help...the fans will go on when the temp near them reach a certain degree and shut off when it cools down enough near the fans. Mine are set at 75 degrees, so set on a lower temp to work as often as possible to keep the air fresh inside the barn.

Vent fans can be a bit loud...a constant drone. Check the box for the "sone" rating...anything a 1.5 or lower will be considered quiet. Anything over that (I think it goes up to 4.0?) will be a bit louder...wiith a 4.0 sounding pretty loud. Mine are a 2.0, so not quiet but not deafening. The horses seem to like the noise, it's a background white noise and they doze off in the cooler air and noise. I don't find it overly loud.

Make sure they have a set in trip or hooked up to a trip in case they overheat.

You'll really like having them. I consider my vent fans to be one of my top fave things in my barn. I can drop the temp in the barn from 95 to 75 in dry heat and down 10 degrees in humid heat. :yes: :eek: :yes: It's almost like air conditioning. And my barn is never stuffy. They don't cost a ton to run unless we have a long heat wave. And they do just fine running for a week straight too. (no overheating)

Do consider putting screens over them on the interior if you use thermostat controls. Otherwise a bird might be sitting in them when they turn on...and that makes a helluva mess. (don't ask, feathers were everywhere!)

And get a duster on an extending pole so you can peal the screen down and dust it off once in a while.

But I'm going to bet you'll think they're the best barn improvement ever once you get them hooked up! :D

Jul. 7, 2010, 12:54 PM
I'm looking at ordering exhaust fans today. My barn is just over 70,000cf. I'm planning on 2 - 48" fans (one at east end, one at west end) that move 19k cf/air/minute. So it will recycle every few minutes.

We have 44" area we can open to put them in about 2' down from the top of ceiling. OR we have 22" x 44" area that is already cut out for ventelation we can put them in but I can't imagine 24" fans will move enough air for how hot/large the steel barn is? If we use the 24" fans in top area then I'll patch the rest of the hole (up to the 44" width- it's already 22" high).

Did you get louviers on your fans? I'm thinking I need to install fans on inside of barn and put louviers flush with barn wall to help keep out rain/snow, etc.

Any ideas?

Jul. 7, 2010, 01:34 PM
Here are how mine are installed:
Exterior close up:

Exterior placement:


They're about 2' down (give or take) from the center ridge.
This was right after they were installed, I've since added screens to the interior to help keep some dust out but mostly to keep baby swallows from getting sucked through.
The screens are just cut from a $6 roll of metal window screen to fit over the fan. We stick the screens onto the exposed screw heads that hold the exterior fan housing on, just shove the screen right on those and it holds great.
I use an extended pole with a brush on it to clean the screens when they get dusty or else just pull them down and hose them off or replace them with newly cut pieces.

Every couple weeks in summer when they run I stand on a muck bucket and using 2 tube extensions on the big-ass back pack leafblower I can blow out the intake of the fan to clear it of dust so the bearings don't grind or the motor blows up before it's time. Takes 2 minutes per fan, very important to keep the fans in good working order.

They're also thermostat controlled and set on trips for safety.

95% of the time they work awesome...like air conditioning in the barn! :D But a day like yesterday....103 here with killer humidity...they act more like an oven-fan...just moving hot air.
Today it's 93 right now and a lot less humid and they vent fans coupled with the stall fans:
make for a nice breezy cooler stall. :yes:

Jul. 7, 2010, 02:08 PM
Sorry.. this is the type of fan I was talking about. I have the roof vent fans- they don't move enough air (don't have enough- would need at least 10-12 of them to help- barn too big). http://www.globalindustrial.com/p/hvac/exhaust-fans/exhaust-and-supply/48-galvanized-wall-master-exhaust-direct-drive-1hp

Jul. 7, 2010, 02:30 PM
Ooo those will move mega air! Around here the cow palaces have those...as do large hay buildings and warehouses.
I'd love to use those as end eave vents, but that size would make my entire barn airborn! :eek: :lol: :eek:

I would think louvres would be beneficial.

Jul. 7, 2010, 02:39 PM
I have mine installed now. Unfortunately my husband put himself in charge of this project and he purchased the fans before giving me input. (Because he knew I woudl want bigger/more expensive fans!!)

We have 12" diameter fans installed in the gables on both ends. I woudl have gotten larger fans, at least 24" diameter, but our installer says these will completely change out air every 10 minutes. I am not sure that is enough. We got them right before we had huge rainstorms and it's been generally cooler, so too soon to tell how much they really help. It does SEEM to me there is more cooler air moving around - I think as the fans suck the hot air out, they are bringing in cool air and making more of a breeze through the barn.

We already had a screened louvre at one end for air circulation, and he mounted one just directly behind that inside the barn. He purchased a set of louvers for the other one. They are not automatic - they have plug-in cords, but we already had a plug almost directly beneath where they were installed. I would have chosen ones on a thermostat.

Jul. 7, 2010, 05:29 PM
I'm eyeing a solar powered gable vent fan at Home Despot...