On Tue, 14 Jul 2020 05:58:19 -0700 (PDT), TimR
wrote:

On Monday, July 13, 2020 at 8:38:13 AM UTC-4, trader_4 wrote:
On Monday, July 13, 2020 at 8:07:39 AM UTC-4, TimR wrote:
The purpose of the filter is to protect the equipment, not the people. You want to keep the coils clean.

The air that hits the filter comes from inside the house. You've already breathed it.

I thought it was actually both. And that to protect the eqpt, even a
minimal filter will do that. That's why they put a spot for a 1"
filter in the typical furnace. To filter out allergens, finer particles
requires the higher rated filters. I've liven for many years in homes
that just had the 1" filter, never had any eqpt problems.

That's what I think, too, but it makes sense to me that filtering finer particles means more resistance to air flow which requires a bigger fan which uses more electricity etc. And if your resistance to air flow is too much you starve the coil of air and you get freezups.

I use the 1 inch filters and I change them when I hear the air noise increase.

I think my refrigerator coils catch the most dust anyway.

The pleated paper filter, like a Space Guard have a whole lot more
surface area so it makes up for how much restriction there is per
square foot. I still have a pre filter in front of mine to stop the
big stuff. That one is washable. There is a gauge on the plenum to see
when the restriction becomes excessive. I usually swap out the element
at around 0.2-0.3" H2O. A new filter cruises at around 0.07".