[JSH]

Originally Posted by freebeard

www.grainger.com/.../kh-what-is-merv-rating-air-filter-rating-chart



The pores are smaller. Doubling up halves the pressure required.

I've got a 1/3 HP fan blowing directly into a MERV 11 14" square filter. It bows out in the center as it clogs up.

The first filter, from March lasted 6 months, the second one lasted 3 days.

I actually found 2 filters. They were the pricey 20 x 20 x 4 filters at about $35 each. Since they are 4 inches thick instead of 1 inch they have a lot more surface area so they should last longer than a 1 inch filter before clogging.

With that in mind I'm debating whether to use them both at once in a v shaped duct or one at a time in a square duct. Either way I'll have to make some cardboard ducting to adapt the square filter to a round fan. I'm thinking that if the smoke blows out of the valley this weekend as predicted I may be able to return one of the filters.

Thoughts anyone?

EDIT: This guy did some experiments with commercial vs homemade air purifiers.

https://www.shophacks.com/newsletter...tion-systems#/