[ddsrph]

The two air handlers for the 1 1/2 ton heat pumps I am looking at have built in
Areas for 15 by 20 filters. They will be sitting on a custom made return air box with a filter on front. From what I have read 300 sq inches is what I need so the 15 by 20 is OK. Would a 15 by 20 filter on front plus a internal 15 by 20 filter be a good idea? The plan is to use non overly restrictive filters and consider the front mounted filter a prefilter with the second catching anything that slips thru.
Please advise on the best thing to do in this case as to number and size of filters.
The return air box can be made with a filter larger that 15 by 20 if needed.

Thanks
JM

 

[SeniorSitizen]

For the past 6-8 years I've run a washable pre-filters in conjunction with the fiberglass filters and the pre seems to catch nearly all the renegade material that needs corralled. I change the fiberglass semi annually and as we can see the new fiberglass appears very similar to the fiberglass that ran for 6 months.

I've never known for sure what the pre material is other than it's very coarse and is blue. It came as a roll in an auction box of STUFF so I tried it and liked it.

 

[supers05]

Shouldn't be a problem. Check your temp rise (dT) with and without the extra filter just to be on the safe side.

 

[beenthere]

If you can make the filter opening take a 20x20 filter. That will give you a velocity of 266 FPM through the air filter, which provides better filtration. Plus allow you to use a MERV 8 or 10 filter in the return air box. No need for 2 air filters.

 

[ddsrph]

I think I have room for that.

Thanks
JM

 

[ddsrph]

Beenthere
I bought a 20 by 20 filter grill today and it will work perfectly. The air handler will be placed on top of air box and then I will make a custom box for top to connect to the 12 inch elbow. I am making the air box a built in with a easily replaceable 3/4 plywood top so I can re-adapt to any future airhandler. The framed in return box will be lined with sheet metal. Here is a before photo.

Thanks
JM

The top two thirds of the closet will have a 24 inch wide door.