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Old 05-02-2012, 05:01 PM   #1
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Filtering Fresh Air System?


Hello All,
Can anyone suggest how to implement a filter on a fresh air system? I am in the process of installing an Aprilaire 8126 with 6" flex duct and would like to filter the incoming fresh air, even if only minimally.

I had thought about building a box made out of ductboard with a slot for adding a replaceable filter, but have a few concerns.

1) Can I use a standard filter or do I need a special filter, given the fresh air system is located in the attic and only runs occassionally during the day? The filter needs to last for several months at a time also.

2) If this is practical how would you suggest creating a sealable door for the filter?

Thanks, Ralph

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Old 05-02-2012, 05:12 PM   #2
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Filtering Fresh Air System?


Do you have a regular A/C filter in the air handler right before the blower ? If you do, then you don't need one for your fresh air exchanger.

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Old 05-02-2012, 06:39 PM   #3
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Filtering Fresh Air System?


On commercial units. The economizer filter, is just a metal mesh screen. more of a rock catcher then anything.
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Old 05-02-2012, 07:53 PM   #4
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Filtering Fresh Air System?


Quote:
Originally Posted by clocert View Post
Do you have a regular A/C filter in the air handler right before the blower ? If you do, then you don't need one for your fresh air exchanger.
No. There is no way of using the air handler slot as they ran the refrigerant lines in front of it. It is located in the attic as well.

We have a single 24in x 24in return filter grill inside the house. That is actually a little small for a 4 ton unit so I plan on adding a second return (ceiling) in our master bedroom, which raises another question.

1) How large of a ceiling return grill can I use if fed with a 6in flex duct? The flex duct will connect to my main return in the attic about 12 feet away.

2) I prefer to intall the return as shown in the diagram but will it be to close to one of the supply vents (9 ft)?

3) In regards to the fresh air filter. I could install a media grill, such as THIS, on the side of our attic return or even build one out of ductboard onto the side. Is any of those viable options? I just don't know how professional the later would be considered nor how to seal it?


Benthere, I would prefer a filter that could offer some protection from dust and polen at a minimum. Would a charcoal type filter on the outside fresh air hood suffice for such?

Ralph
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Last edited by Ralph III; 05-02-2012 at 07:56 PM.
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Old 05-02-2012, 07:59 PM   #5
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Filtering Fresh Air System?


This is the media rack example as found here.
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Old 05-02-2012, 08:02 PM   #6
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Filtering Fresh Air System?


Make up a small filter box close to the return plenum. Something in the range of being large enough for a 10X10, or 12X12 air filter. Putting a filter at he intake hood would make it too small to last for long.
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Old 05-02-2012, 11:14 PM   #7
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Filtering Fresh Air System?


Quote:
Originally Posted by beenthere View Post
Make up a small filter box close to the return plenum. Something in the range of being large enough for a 10X10, or 12X12 air filter. Putting a filter at he intake hood would make it too small to last for long.

Yes, that is exactly what I was thinking of.

I could cut a hole into the side of our existing ductboard plenum, let's say 10 x 10, and then frame out a three sided box over that in accomodating a 12 x 12 filter. The fresh air flex duct and damper would then connect to that (see diagram).

The metal media rack I linked to would be nice because it has a sliding door for the filter. On the other hand, I have some ductboard on hand and that wouldn't cost me anything. The only issue is how to create a sealed door with ductboard? Maybe I could use a hinged metal strip with weatherstripping? Any ideas there?

What about my proposed return ceiling grill in the master bedroom? Would it be ok to locate that within 8-9 ft of a supply grill or is it a must to put that on the opposite side of the room?

Benthere, I feel like you've done as much work on this project as I have! Thanks man.....


God Bless
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Last edited by Ralph III; 05-02-2012 at 11:17 PM.
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Old 05-03-2012, 04:33 AM   #8
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Filtering Fresh Air System?


As long as the return isn't over sized for the room, you can locate it there. It will tend to allow some of your supply to be draw out of the room instead of fully mixing, but probably won't hurt anything.

For a door for a filter slot on duct board. Works fairly good if you make a metal cover for the slot, that goes into the slot an inch, and has a 1 inch tab around it with some thin weather stripping.
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Old 05-03-2012, 10:15 AM   #9
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Quote:
Originally Posted by Ralph III View Post
1) Can I use a standard filter or do I need a special filter, given the fresh air system is located in the attic and only runs occassionally during the day? The filter needs to last for several months at a time also.
If you are not afraid of making custom housings etc you may consider using some vehicle parts. Just make sure you are not using a Bentley air filter and you are good. This guys are all weather and last forever. I'm serious.

That may resolve your sealing problem too.
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Old 05-05-2012, 11:48 PM   #10
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Filtering Fresh Air System?


http://www.hvacquick.com/products/re...P-Filter-Boxes

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