I have a new package unit I want to take care of. I currently use a Boair electrostatic washable filter. Says it is .10 wg resistance.

I have a 12x36x1 return grill. I have a 3 ton pkg unit. I just noticed that my Boair filter is sized 11 1/4 x 35 1/4 x1. I had about a 1/4 inch space around filter that was pulling air into return duct. I put a 1/4 inch high density foam weatherstrip around my filter to make a better seal. Good idea?


Would it be better to allow some air to bypass if I use the Boair filter?
I am waiting on an Accumulair Merv 6 pleated. Would that be a better choice for airflow?

Is $7-$10 per filter per month a reasonable expense? (I haven't bought a filter in last 10 years)
Should they really be changed every month?

Follow the manufactures instructions for the filter you choose. They have much more knowledge than we do here about there own product.

Follow the manufactures instructions for the filter you choose. They have much more knowledge than we do here about there own product.

For 3 ton unit with nominal CFM 1200
Trane says it should be 4 sq.ft.* whereas I have 3 sq. ft.( I cannot change this. House was built in 1967 with 2.5 ton unit and return air grill in ceiling). Filter resistance .05.
"*Filters must be installed in return air system. The above sq. footages are based on
300 F. P. M. face velocity. If permanent filters are used , size per mfg. recommendationswith clear resistance of of .05"WC."

Follow the manufactures instructions for the filter you choose. They have much more knowledge than we do here about there own product.

I noticed some "dust" has been bypassing filter and accumulating on black fuzzy insulating material that lines return grill box in ceiling. Is this normal to have some air seeping around sides of filter? Will this "dust" cause any problems either to AC unit or return box ?

Filters are not perfect.
Add more return air (yes it can be done)
You also have to deduct 25% for the grill restriction in order to calculate your return air duct size.