Exhaust fan search

[LSVLance]

While not really Heating and A/C, this question is ventilation related so thought this might be the best place for it.

I'm looking for an exhaust fan to mount in the drywall ceiling of my 3 car garage attached to the house.

My hillbilly "box fan in the access hole" experiment has proved effective in removing car heat from the garage so I'd like to take it to the next level with a more "permanent" solution.

The trouble I am having though is finding a fan that can be mounted horizontal that will work with just 200 sq in of open inlet air. The closest I have come is a 24" fan that needs 864 sq in of inlet air.

http://www.airvent.com/index.php/products/whole-house-fans/direct-drive-fans#specifications

• The WH242ML 24-inch direct drive whole
house fan requires a minimumof 6 square
feet, or approximately 864 square inches, of
open attic vent area.

I have two 8" x 12" vents (192 sq in) coming into the finished garage and four 5" x 22" attic vents (440 sq in) leaving the attic. I am not really looking to cut holes in the walls or roof to accommodate a fan at this time.

Using this calculation it looks like I need about a 400 CFM fan max.

http://www.airvent.com/index.php/pr...gable-mounted-power-attic-vent#specifications

To give an example of what I am trying to do here, on a 105 degree day here, if I park my recently driven Jeep or Truck in the garage...by late afternoon it can be 122-125 degrees inside the garage. If I raise the hood of the driven vehicle and turn the box fan on...it'll stay right around the ambient outside temperature inside the garage...which I am happy with.

If anyone has any ideas on a fan to try...I'm all ears...

 

[rattle_snake]

...I am not really looking to cut holes in the walls or roof to accommodate a fan at this time..

Perhaps not helpful but I still recommend going through wall up at ceiling not attic for a permanent solution. Since you already have intake vents you are half way there.

Either way you have to deal with wiring, suggest putting whatever fan on timer and run as needed plus early AM when outdoor air is coolest. good luck.

 

[LSVLance]

The house is U shaped and three walls of the garage are all "pretty" and plainly in view from driveway, front of house and courtyard... The Wife Acceptance Factor of putting and exhaust fan on one of those walls is very low if you get my drift...

The box fan in the attic is working very well, I'm surprised actually at how well.

I planned on wiring it on a thermostat and setting it pretty high. I'm not trying to make it cooler than outside air, just trying to keep it out of the 120s in there...

 

[Fixin'Stuff]

The trouble I am having though is finding a fan that can be mounted horizontal that will work with just 200 sq in of open inlet air. The closest I have come is a 24" fan that needs 864 sq in of inlet air.

I have two 8" x 12" vents (192 sq in) coming into the finished garage and four 5" x 22" attic vents (440 sq in) leaving the attic. I am not really looking to cut holes in the walls or roof to accommodate a fan at this time.

You need to know the "net-free area" of those vents. You can't use the size of the hole for the measurement. Quite a bit of the area is taken up by the grille and screen. For example, Home Depot lists a 16x8 soffit vent that one might assume has 128 square inches available. But the spec lists the actual net-free area at just 65 square inches. https://www.homedepot.com/p/Master-...-Eave-Soffit-Vent-in-White-EAC16X8W/100023618

You're getting down in net-free area size to where a mid-size bathroom exhaust fan would probably be sufficient.

 

[LSVLance]

I think I've found a "build your own whole house fan" source...

I think I can make a cabinet of sorts to mount this fan to up inside the attic

https://www.globalindustrial.com/p/...xhaust-fan-gmf-10a-115v-1-25-hp-595-cfm-steel

and put this shutter in the ceiling which the fan will pull open when on and springs will help it fall closed again when fan goes off.

https://www.globalindustrial.com/p/...minum-supply-intake-wall-shutter-12-cwv-12x12

I have a few questions and a few other options to choose from but I think I can make this work.

With a variable speed controller I bet I can adjust the fan to match the intake vents plus air that leaks in around the big and little garage doors so they all work together.

 

[PassnThru]

Can't you just crack the garage doors a bit? I have a whole house fan like you posted in my garage - it's usually running when the doors are open. I will occasionally run it at night with 3 windows open. I have absolutely no idea if that meets the requirements but it has been running trouble free for 15 years. All it will really do is cause it to run slower which will probably shorten the life some.

 

[u3b3rg33k]

what about this?
https://www.northerntool.com/shop/tools/product_200510953_200510953
rated 1100cfm
?

fans typically run faster when unloaded - unless it's a positive displacement blower.

 

[like2wheel]

The 2 speed version of that whole house fan (WH242MLX?) would surely need less vent space on low speed.
I have a similar fan that is 2 speed & belt driven. You could change the pulley sizes to slow it down even more.

It is a good idea to have a method that automatically shuts off the fan in the event of a fire.

 

[LSVLance]

Can't you just crack the garage doors a bit? I have a whole house fan like you posted in my garage - it's usually running when the doors are open. I will occasionally run it at night with 3 windows open. I have absolutely no idea if that meets the requirements but it has been running trouble free for 15 years. All it will really do is cause it to run slower which will probably shorten the life some.

I thought about that except my doors face due West and the hot afternoon sun baking the doors and driveways would be the first air it would pull in. My vents are on a North facing shaded wall and my thought it the air it would be pulling in from there would be much cooler and more effective.

what about this?
https://www.northerntool.com/shop/tools/product_200510953_200510953
rated 1100cfm
?

fans typically run faster when unloaded - unless it's a positive displacement blower.

That is a pretty good option...except for the price...

The 2 speed version of that whole house fan (WH242MLX?) would surely need less vent space on low speed.
I have a similar fan that is 2 speed & belt driven. You could change the pulley sizes to slow it down even more.

It is a good idea to have a method that automatically shuts off the fan in the event of a fire.

I agree... I'm looking at this one to install with whatever fan I choose...

https://www.amazon.com/dp/B002TYK4A6/?tag=atomicindus08-20

Garage also has built in sprinkler system so hopefully it'll never get used.

 

[LSVLance]

I'm wondering if I"m not just over thinking this a bit?

Why not just get a normal whole house fan and slow it down with a variable speed controller to get it to pull the CFMs my vents will allow?

The old "tissue paper in front of a vent" trick along with opening up the door right next to the vents should let me dial the speed into "just right"...

 

[Marctrees]

https://www.jdmfg.com/es-shutter-fan

Order from Global Industrial for best price.

My recent order from there - Marc


B1377898 J&D Wall Mount 5 Amp Variable Speed Control Switch 120V Control Up To 4 Fans UPS - GROUND 2 $26.50 $53.00
B968399 J&D ES Shutter Fan 24", 115/230V, 1/2HP, 1PH, Variable Speed, Aluminum Shutters UPS - GROUND 2 $245.95 $491.90
Item Total: $544.90
Tax: $49.90
Estimated Freight: $60.01
PLEASE BE SURE TO REVIEW OUR TERMS AND CONDITIONS *Total: $654.81

 

[Fibersport]

Why worry about matching the com of your vents? They will only allow so much through them, the rest just builds up pressure, much like a funnel when you pour water through it. Whatever that doesn't flow through fills up into the funnel.

 

[Marctrees]

I do NOT know if this is correct - But I'm pretty sure I recall reading in more than one place... ends up you need ballpark 4 x the free sq area of intake venting of the power vent area to not restrict the outgoing.

I'm pretty sure actually J&D told me that when we selected our above fans and were planning for intake venting.

They have good old school WS country boys answering their tech phone.

Kinda rambling here, but may want to look into that.

Marc

 

[rattle_snake]

The Wife Acceptance Factor of putting and exhaust fan on one of those walls is very low if you get my drift...

I planned on wiring it on a thermostat and setting it pretty high. I'm not trying to make it cooler than outside air, just trying to keep it out of the 120s in there...

Ya I get it, I have same constraints at times


As for the t-stat, it may or may not do what you want at a single set point. I assume your going to have it sense temperature of the garage not the attic. I think you would have to set it above the max outdoor temp (>125F) or it will run for long periods.

Another option is a differential t-stat, but I have found a timer is much simpler and works better to achieve my goal of turning on fan when it is needed.
I use the type that fit in a standard single gang box like a light switch, available at HD. East to turn on at any time, and could program to run automatically when you get home or whatever.

I have a Canarm 16" variable speed fan in my shop. It uses a simple triac for control, but if set too low can stall the fan on startup or high wind conditions (aka static pressure on outlet). If it stalls it will overheat at locked rotor current.
To do it right you really need a decent 3phase/brush less variable speed motor and PWM controller but they are not cheap.

My fan needs about 10x the intake area to not be restricted. My vents are only about 2x which works OK but...

 

[yeldogt]

Get a roof or inline fan for a range --- 1200cfm -- 10" pipe. look on ebay

 

[grumpyvette]

home depot sells a roof exhaust fan

my garage is roughly 2900 sq ft and the two I mounted on the roof are able to clear the air from the shop in about 10-12 minutes As soon as the budget allows Ill add two more


its listed as...
1500 CFM Shingle Match Weathered Wood Power Roof Mount Attic Fan

Helps cool attics up to 2,800 sq. ft. in size
Compact size with hemmed dome for a sleek look
High efficiency motor with adjustable thermostat
$124.00

 

[SGKent]

because of fire hazard you do not want to vent to the attic. You want to vent to the side wall farthest from the house. If studs need to be cut to create a box for the fan then you need a permit and structural drawing of what you want to do. The hole in the ceiling should be sheet rocked or sealed metal door installed to keep a car fire from climbing into the attic. The venting of the garage should create a negative pressure in the garage so that if the house door to the garage is opened and there is a fire going, smoke and flames are not drawn into the house. The same is true when the car fumes etc are in the air after it is turned off. You can put a switch in and a motion sensor so the fan can be turned on manually or when you pull in it automatically comes on.

I personally like Triangle Fans of Arkansas. They make models with exterior louvers that open and close with pressure from the fan. http://trianglefans.com/general-purpose-fans/


Avoid venting into the attic due to fire risks.

.

 

[LS6 Tommy]

No one has mentioned two things-
1. Doing that eliminates the fire block between the garage and the house and is most likely also a code violation. The fan has to have a fire damper.
2. Although it's not illegal, that's a great way to allow vehicle exhaust into your attic if you don't have enough free air flow out the vents.

Tommy