Filtering Pollen from Air Exchanger Intake Duct

My son has Asthma, and it's aggravated by seasonal allergies. We've taken steps to limit allergens from entering the house - we keep the windows closed most of the time, we've sealed air leaks and we've added a mechanical air exchanger with heat recovery. I wanted to improve the filtration of incoming air to try to ensure we're removing pollen and other potential irritants. I decided to to add supplemental filtration of the air exchanger intake duct.
Fantech FB6 Inline Filter Box - Designed for 6" Round Duct
This is a fairly simple project. Find a location on your incoming air duct where you can remove approximately 26" of the round duct, and mount the steel filter box. Ideally, locate the filter box close to your other air handling equipment, so that it is easily accessible for filter changes during routine servicing. The specifications of the FB6 are as follows, check to see if these are appropriate for your installation or if you require a different size.
• Airflows up to 176 cfm
• 6" diameter plastic duct connections
• Beige powder coated
• Neoprene door seal
• Access door removed with thumb screws
• Weight - 10.6 lbs
• Filter compartment dimensions - 19 1/2 x 10 x 8
• Filter size - 20 x 10 x 1"

Filter Box located close to HRV to simplify servicing and filter changes
One thing to note about this filter box is that it's not insulated, so if you're operating this in cold climates, you'll get condensation on the box. In my case, I wasn't too concerned about this because the box is located above a concrete floor in the utility room, about 24" from the floor drain. I've considered insulating the box, but haven't gotten to that because the condensation doesn't cause too much of a problem.
Data Plate on the Filter Box
Once I installed the external filter box, I removed the smaller incoming air filter from the air exchanger, because there is no need to filter the air twice. You can select your level of filtration depending on your needs, in my case I'm using MERV 11 filters which I find is a good balance between filtration and pressure drop. I also want to maximize the airflow, because my air exchanger is a bit undersized for the size of my home.


Works fine, condensation on the box doesn't cause any problems in my installation, and I can tell the filtration is working well by the amount of crud the filter pulls out of the air. I change filters four times a year. 

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