MERV11 for Box Fan Filter Build?

[Jon Singh]

Hey guys,

Thinking about building out a few Box Fan Filter builds, I saw that some companies sell 'cleanable' MERV 11 filters, I was curious if anyone who's build these or researched this before think thats good enough? I like the idea of just spraying the filter down and cleaning it every once in a while.

Thanks,
Jon

[Jack Frederick]

11’s are good filters, but not near hepa’s specs, as you know. Perhaps stage filter grades. Run the 11’s and try some higher rated units in another box. Where the 11-13 rated filters had a problem was in ducted systems. Folks throw an 11-13 in their central system and the static pressure goes through the roof. In an open fan box you do not have to account for duct pressure drop. It should be a good experiment. Please keep us posted on results

[Andy D Jones]

At MERV 11, it would take a lot of passes of the room air through the filter to get good filtration, especially on the fine (0.3 micron) dust. During that time, a fair amount of the dust will settle out on its own, onto bench or machine tables, the floor, etc., to be stirred up into the air again later.

But one of the features of an air cleaner is that it continues to filter the room air multiple times if it is run long enough (unlike a dust collector filter, which pretty much gets one pass at the dusty air). However, an air cleaner can't filter any dust that has already settled out, unless/until it is stirred up again.

Personally, I'd look for a higher MERV rating, but HEPA (or > MERV 16) is not really necessary on an air cleaner. HEPA filtration is a good goal for a dust collector.

-- Andy - Arlington TX

[David L Morse]

11’s are good filters, but not near hepa’s specs, as you know. Perhaps stage filter grades. Run the 11’s and try some higher rated units in another box. Where the 11-13 rated filters had a problem was in ducted systems. Folks throw an 11-13 in their central system and the static pressure goes through the roof. In an open fan box you do not have to account for duct pressure drop. It should be a good experiment. Please keep us posted on results
Actually, an axial fan has much less static pressure capability than a centrifugal fan. I measured a cheap box fan at 990 CFM. Adding a MERV 12 filter dropped that to 220 CFM.

As Andy alluded to, it's not the filter efficiency but rather efficiency times CFM that's important. I have some data if you're interested.

[Jack Frederick]

Thank you, David, but I follow along on filtration posts as they occur. I guess, in view of your information, what is the best configuration to use the 13’s effectively.

[David L Morse]

From a performance standpoint a furnace blower in a box with the filter will do the best. Lacking the blower or the room for the box with the blower a box fan with an attached filter will work. It will just take longer to clear the air.

[Jon Singh]

Thanks all, higher MERV rating it is!

[Ole Anderson]

I will give a +1 to David's comment that a box fan is a poor choice for an ambient air filter, you just loose too much air flow with the restriction of even a cheap filter much less a MERV 13. Been there.