Air Filtration Unit in Attic?

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Forum topic by chopnhack posted 03-08-2012 02:37 AM 5477 views 2 times favorited 38 replies Add to Favorites Watch
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375 posts in 3312 days

03-08-2012 02:37 AM

Topic tags/keywords: air filtration air filtration air cleaner cleaner attic mounting ducting grille ceiling filters

I have 8’ ceilings in my garage and the thought of losing some overhead space to one of these gargantuan air filtration units is a bit much :-) Has anyone ever thought or actually put one of their’s up in the attic? I ask because I have fairly good access and would be able to get up to it to change filters and what not. The loss of the remote feature would be a bummer..

I was thinking about mounting it in the attic and ducting the intake and exhaust down through the ceiling with their respective sized grilles.

What are your thoughts?

-- Sneaking up on the line....

38 replies so far

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#1 posted 03-08-2012 02:51 AM

I hate to piggy-back on your question but I am interested too as i would like to do the same!

-- "It's fine in practise but it will never work in theory"

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#2 posted 03-08-2012 02:55 AM

The only problem that I can think of would be if the attic temperature gets extreme in the summer, it might over heat the fan motor.

Many HVAC have attic and roof mounted units, so we know it is possible.

-- Joe

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#3 posted 03-08-2012 02:59 AM

This is a good point Joe, the commercial unit would be easier to just buy and put to use, however, for the price it might not be a bad idea to get for ~$100 one of those 1500cfm attic fans from the big box stores and perhaps build a plywood box… hmmm lots of thinking to be done!

I wonder about the differences between squirrel cage fans and the open impeller design – isn’t there a pressure difference at the given cfm between these two types of fans?

-- Sneaking up on the line....

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#4 posted 03-08-2012 03:10 AM

Most of the blower systems in my area are direct drive. These have the motor in the housing with the squirrel cage. This would have the room air traveling over the motor so it should be about the same temp as the room below. You want to put the filters on the suction side of the blower. These are designed for restriction on the suction side. You might be able to build the system in a way that would have the filters changeable from below with a register in the ceiling that opens. Then make a return thru the ceiling into the room…...?

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375 posts in 3312 days

#5 posted 03-08-2012 03:17 AM

Good point Grandpa, but wouldn’t having the filters hanging face down lead to dust dropping back down into the air when the unit is turned off?

What about fire codes? Anyone know if this would be a violation of code based on this being an attached garage?

-- Sneaking up on the line....

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#6 posted 03-08-2012 03:41 AM

See my reply on BT3Central…

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#7 posted 03-08-2012 01:29 PM

You can buy filter frames or have a pan built that will hold one of the 4” thick “Air Bear” filters. Then duct that up to a fan cabinet in the “attic” whose discharge goes back to a ceiling diffuser in the space. The air from the lower space will be cooler so it will cool the motor when operating. As for the blower type it needs to be a squirrel cage type. Propeller fans don’t create enough static pressure to overcome the resistance of the filter media.

-- OK, who's the wise guy that shrunk the plywood?

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#8 posted 03-08-2012 04:47 PM

Yes on squirrel cage fans. I have seen filters with an inch of dust on them. They were vertical. I think the dust will cling to a filter even with it being flat or horizontal. they might be messy to change but think about going into an attic to change a dirty filter. I have some of these blowers and plan to build filter systems. I plan to use some replacement filter sold for the commercial systems. These filters remove the fine dust down to .5 micron. The pre-filters will stop the larger particles and these will remove the fine dust. Haven’t started these yet but I am reading all the threads on the subject. I have been given 3 blowers by a friend in the A/C business.

View crank49's profile


4032 posts in 3889 days

#9 posted 03-08-2012 05:04 PM

Be sure to direct the air coming from the unit away from the intake or it might just circulate the same air over and over.
Would not hurt to insulate the outside of the filter case in the attic.

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375 posts in 3312 days

#10 posted 03-08-2012 06:32 PM

Good point Bob about the squirrel cage. I read somewhere that the thicker filter media do not filter any better just have a longer life span as they can hold more dust.

Good info Grandpa, buddied you up, please post when you begin or blog your project!

Crank49 – this is something someone brought up on another forum where I post

“mpc – The ceiling mounted air filters work best when they can get the shop air moving in a circular pattern I believe. So your ducting would ideally be in the walls and/or have elbows to divert the airflow to along the ceiling. If the vents were just flush mounted to the ceiling the effectiveness of the filter would be greatly reduced I believe. One area directly below the intake might stay clean… and whatever was directly below the exhaust would get blasted clean but everywhere else probably would be worse than no filter at all. And the ducting itself would lessen the total airflow of the filter unit, just like excessive pipe length hurts dust collector performance.”

A very good analysis, but I think if the squirrel cage was of decent strength there would be sufficient pressure to get the job done.

A limiting factor would be that you would still need to drop an elbow out of the ceiling to blow the air to get that circular flow… a simple ceiling diffuser would only direct the flow straight down and then reflect up creating cells, rotating in the vertical plan, but no horizontal plan rotation. Now we are starting to get into the deep end, lol.

I appreciate your comments and thoughts. I think that this would be ideal for someone building a shop or renovating one with stud walls, they could then incorporate wall vents to create the circular flow without losing valuable shop space.

-- Sneaking up on the line....

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3263 posts in 3593 days

#11 posted 03-08-2012 06:33 PM

I agree with Crank49 on the circulation. I had been thinking about this and I believe a piece of sheet metal flashing could be fashioned to fit between the 2 openings and it would become a deflector. This is if you have plenty of head room. Don’t make something you might be injured on. A second register would help also. They have louvers.

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3263 posts in 3593 days

#12 posted 03-08-2012 06:49 PM

Chop, I think if you are using pleated paper filters for the primary or first filter the larger or thicker filters has more filtering surface. the pleats go deeper. If you go to a hardware store and look at filters you will notice that the cheaper pleated filters will have the points an inch apart (a distance for talking) and the more expensive filters will have the pleats 3/4 inch apart. more filtering surface so they should last longer. On my air conditioner I change them every 30 days so that is taken care of there. with a shop air filter I think you should have one of those then a static type filter behind it then the .5 micron filters in the back then the blower. I might be over filtering and cause too much restriction. I am not sure. I was told that if you want to use the blower from an air handler as a shop fan you should block about hold of one end of the intake (25% restriction) because these are designed for the restriction in the filters.

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375 posts in 3312 days

#13 posted 03-08-2012 07:06 PM

Valid point on the circulation Granpa, I think my wife’s friend from grade school is an hvac engineer… I think if I can create a set of cohesive questions I will send him an email with a sketch of what we are talking about to get his input. Would be great if he could model the airflow of one of these contraptions for a given room. Really is the deep end now, hahaha ;-)

As for the filter, here is where I got the information: <<

Conventional 1” fiberglass throwaway filters

Found in most residential and small commercial applications. Lowest first cost, but least effective. Many are coated with an adhesive substance to help collect dust. For this reason, this type of filter should not be cleaned in any way to “extend” its life. The dust and adhesive are both removed when cleaned, rendering the filter almost useless.

Conventional 2” fiberglass throwaway filters

Commonly found in some commercial applications. Although it is twice as thick as a 1” filter, it is not twice as efficient; it only holds more dust.


And as you said, the should last longer, and they do because they hold more dust, however, I don’t believe they filter any better and are probably more restrictive.

-- Sneaking up on the line....

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#14 posted 03-08-2012 07:38 PM

Chop, there would only be code issues if there is an air transfer from a conditioned to non-conditioned space. Sounds like that don’t apply to you.

What about framing up a plywood plenum on the attic floor, and placing the unit inside? Most of us can do plywood better than sheet metal. Do you really need to insulate, since you live “somewhere sunny?”

I did something slightly similar for my whole house fan, placing a caulked plywood box in the attic with a hinged door on top.

-- Christianity, if false, is of no importance, and if true, is of infinite importance. The only thing it cannot be is moderately important. -- C.S. Lewis

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375 posts in 3312 days

#15 posted 03-08-2012 07:47 PM

Thanks for your input Rick! You did a great job with that fan!!

I think someone else mentioned insulating, however, it goes to your point to ensure there is no venting of inside to outside air for fire reasons. As for insulating, yes its a good idea, it would be for heat reasons, it gets hot here!

Because of vibration, I think I would isolate the unit on rubber pads and not screw directly from unit through pad to framing breaking the direct connection for vibrations to travel. Your unit looks like a belt driven model so its probably very smooth with no vibration.

-- Sneaking up on the line....

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