you need to evaluate the airflow restriction with the tighter filtration that occurs with making this change. In particular as the filter loads it will become more restrictive.....so the answer depends on how frequently you change filters and your overall system.

You could also look at adding UV lights and keep the same micron level of filtration that you have.

Hi Julie...thank you! After researching a bit I found that that could be an issue. I will ask my guy about it.

I wouldn't go above a 7 and I would also upgrade to a 4-5" thick filter which makes a huge amount of filter media in comparison to a 1".

I would also evaluate or have someone else evaluate the duct sealing. If the ducts are sealed with mastic and no outside air and worse yet attic air with insulation fibers and dirt being pulled into the return vents and recessed lights could be the real issue. I don't care what combo of filters and or lights you use, the problem will not go away. With leaky recessed lighting just opening and closing doors will pull crud out of the attic in for you to breathe.