[Shop-talk] Furnace Filters

[Jeff Scarbrough]

I have a deep filter housing (this kind
https://shop.aprilaire.com/products/aprilaire-401-replacement-filter  ) and
I get a year or more out of them.  They are MERV 10, and the system is
designed for them.  A deeper filter has more surface area, so it can
collect more dust before restricting air flow.

I'm kind of in the filter business, as I help manage a high-containment
biological research laboratory where keeping things in their place is very
important.  We have hundreds of HEPA filters, plus the gamut of regular and
bag filters from MERV 8 to MERV 13.  In general, we determine when
replacement is necessary by measuring pressure drop across the filter.

I don't do that at home, but you all have got me to thinking I should. I'm
general, though, the performance of the system will inform you.  Too much
restriction (from a loaded filter, or just too many of them in the train)
will eventually cause noticable problems.



On Mon, Dec 13, 2021, 19:03 Jim Stone <1789alpine at gmail.com> wrote:

> Thanks, guys.  That is all good feedback. David: I hadn’t considered using
> a washable filter, but it is an interesting idea.  It looks like a 4” one
> will cost me around $100, so the breakeven point is after a year.  Not too
> bad.
>
> But, here is an interesting point that showed up tangentially when I
> Googled “washable furnace filters”:
>
> Fortunately, most 20x25x4 air filters last between *six to eight months*.
> By that calculation, the average homeowners will not need more than two
> 20x25x4 air filters in any given year. In contrast, a one-inch air filter
> will need to be changed every two to three months.
> https://servicechampions.com/benefits-of-a-20x25x4-air-filter-installed-in-your-furnace/
>
>
> If that is true, the cost difference between the 4” and 1” disappears.
> Thoughts?
>
> Jim
>
>
> On Dec 13, 2021, at 5:32 PM, Pat Horne <patintexas at icloud.com> wrote:
>
> My shop air handler is set up to use a 2” filter but the installer said to
> use 2 one inch filters, both good ones. I watch the first one & remove it
> when it is too dirty, move the second one up & install a new second one.
> There is some discoloration on the second filter, so it is doing
> something.
>
> If you want to go with two different ones, I’d put the poorer one first,
> followed by the better one.
>
> My HVAC guy says to not use the corrugated filters, nor the fiberglass
> ones that you can see throughout. He sells me Purolator 312 filters by the
> case.
>
> Peace,
> Pat
>
> Pat Horne
> We support Habitat for Humanity
>
>
> On Dec 13, 2021, at 4:21 PM, Jim Stone <1789alpine at gmail.com> wrote:
>
> The company that installed my HVAC system a few years ago used a filter
> box on the return line that takes 20” x 25" x* 4”* filters, which is an
> unusual, and thus expensive, size - filters generally run about $25 each -
> that is not readily available other than online.  During construction, my
> general contractor just had a cheap 20” x 25" x *1” *filter in there that
> seemed to work just fine.  I checked the installation instructions for the
> furnace and there are no specifications for the filters, other than that
> they need to be changed regularly, which is getting pretty expensive.  Is
> there any reason I couldn’t just use 1” filters, which are less than half
> the price?  Maybe even put two of them in the box, a good one first to
> catch most of the dust and a cheap one like the contractor used as a
> secondary one.  It is a snug fit and I don’t think there is any danger of
> them tipping, but two would make it impossible.
>
> Thanks,
> Jim
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