Furnace Filter

[John105]

our new (june) furnace has a GeneralAire MAC 1400 Filter slot. Requires a GeneralAire 4541 filter. It came with a MERV 11 and I bought a couple of filters. The system reminded me to change the filter after 4 months, and I did. Quite a bit of fine grey dust covering the filter so a 4 month change cycle seems to be right. Filters are **** expensive:

View attachment 186515

The interesting thing is Aprilaire slides into a track, which is why I'm hesitant to install a generic. But, they say they can be used a year.

I think of this stuff as arbitrary--who determines when it needs replacement? And it's like concentrated laundry detergent, they set consumers up to waste money. Why not make it so concentrated one uses an eyedropper?

Anyway I'm not liking 4 for $193 for Aprilaire 413's.

 

[Kantaro]

I built filter fans. Uses quiet bathroom fans to pull air through two 24x24 inch filter.
My pm2.5 meter usually reads about a 0 in the summer.
I use the smallest filtering 3m air filters they sell at Lowes. The purple ones.

You might enjoy reading through Smart Air Blog: https://smartairfilters.com/en/articles/

 

[HowAboutThis]

The interesting thing is Aprilaire slides into a track, which is why I'm hesitant to install a generic. But, they say they can be used a year.

I think of this stuff as arbitrary--who determines when it needs replacement? And it's like concentrated laundry detergent, they set consumers up to waste money. Why not make it so concentrated one uses an eyedropper?

Anyway I'm not liking 4 for $193 for Aprilaire 413's.

View attachment 199852

On our old house that's what we had. I believe they were 6 month or yearly change?

 

[totegoat]

$5.59 filters from Ace Hardware. AC contractor said not to use expensive, restrictive filters.

 

[John105]

$5.59 filters from Ace Hardware. AC contractor said not to use expensive, restrictive filters.

We’ve heard this a million times, including me. My contractor replied when I said, “The cheapest I can find is $3.99.”

He said I’m not looking hard enough.

Why? Let’s unpack the reasoning.

In my case, I had a 1999 furnace with a PSC blower that was failing. There are only limited settings (I believe 3) handled by moving jumpers. The correct speed for heat is the one in the middle.

Per the seller of the home, I was using $8 filters. By 2016, the furnace was short cycling because the PSC motor could not do its job. Contractor set it to high like the AC setting. And told me use $0.99 filters which will be easier on the remaining life of the blower.

Flash forward to 2020, new system, ECM motor and variable furnace. Came with aprilaire 413’s which at the time cost $30+, now $50+.

To convert it back to 1” and use a $0.99 filter to lessen the restriction would be unwise, imho. The unit was designed for these filters and can supply the correct cfm with them. Maybe when 15 years old it cannot and yes, unless replacing the blower, use less restrictive filters.

It would be nice for contractors to explain why they say what they do, so homeowners can make informed decisions. I do realize many things we say and repeat, we know not the context nor the theory behind. Sorta like rumors. My .02 ymmv.

Edit p.s. just thought of this…my wife’s uncle too has a 2009 system with a 4” filter. He refused to pay $20+ at the time and he stacks 4x $0.99 filters in the device. He’s done this for 14 years now so it can be done. I just don’t want to. And yes I would love to save the money. What I don’t know is if his furnace is variable. It might have a PSC.

 

[Hall]

It would be nice for contractors to explain why they say what they do, so homeowners can make informed decisions.

In our previous house, we replaced the furnace/AC and opted for an "air cleaner", i.e. the 4" filter types. Was the new furnace more powerful and able to handle the restriction ? Would it be able to after 20+ years ? I am curious what the difference in furnaces are where you can use 4" almost blanket-like filters vs $3, 1" filters.

 

[MrJayhawk]

The interesting thing is Aprilaire slides into a track, which is why I'm hesitant to install a generic. But, they say they can be used a year.

I think of this stuff as arbitrary--who determines when it needs replacement? And it's like concentrated laundry detergent, they set consumers up to waste money. Why not make it so concentrated one uses an eyedropper?

Anyway I'm not liking 4 for $193 for Aprilaire 413's.

View attachment 199852

If you look closely at description, you are also getting the apparatus to change the box over to accept the accordion filter which is about $30.
I’ve been buying the genuine filters for years and they usually are in the $45 ish range. I change mine out twice a year to be safe.

 

[tcp71]

Changing to a 1" thick filter would save a lot of money even if I changed it monthly. Would this work?

https://www.filtrete.ca/3M/en_CA/p/d/v000162394/

 

[Jdeere562]

Merv 10 last me about 2 weeks, then I can tell the air flow is restricted. I change them often.
Maybe I should vacuum more.

 

[johnmyster]

Has anyone ever messed around with putting a pressure gauge on the “pressure“ side of the filter? It seems I remember seeing that done where?

I put a gauge on my system. Dwyer Magnahelic 4", reads 0-1" of water column. It was $30 on ebay. I ran tubing to measures pressure difference between the inlet (return) duct post-filter and ambient. If you don't want to buy a gauge you can use a piece of clear tubing with water inside.

Our system has an undersized (my opinion) return duct and insufficient airflow is not good for modern heat pumps. I couldn't effectively run anything other than the blue fiberglass jobs. I modified the filter rack to allow a 4" pleated job, which let me move up to better filtration without reducing flow. The blower also uses less electricity (about 100 watts less). I wanted to get better filtration with kids in the house having allergies. The washable electrostatic thing that was there when I bought the house was far too restrictive to keep the heat pump happy in winter. (High pressure trips on long cycles).

I found the "filterbuy" filters (1") on amazon were not too restrictive when new but after a few weeks that would change. I tried their 2" and 4" models but pleat spacing was not controlled and would collapse in use.

I've been running a 4" Glasfloss MERV 10 for almost a year now and pressure drop has gone up very little in that time. They have a "comb" built in to control pleat spacing. It's still nearly as free flowing as the 1" blue fiberglass model at the same CFM setting. The 4" Glasfloss filter is more expensive but the additional lifespan, better filtration, and lower power consumption is a gain. 2 pack on Amazon is reasonable for what I get.

If I ever have our system replaced I'll have the returns and filter rack upgraded to allow a larger filter size. Going deeper on a pleated filter actually gives you more filter area in the same footprint.

 

[Chevyc10]

Your return air grill must be sized properly to use higher Merv filters. Too small and your evaporator will freeze up. I use Merv 13, my system was designed for them and no issue. Sams runs Filtrete on sale frequently, check online site. Amazon has good prices, sometimes they arrive damaged. Refund issued, they have improved shipping cartons, no damage lately.

 

[UncleDave]

We live in an area that has forest fires within 50 miles almost every year. That's why I like running MERV 10+. But I might drop to 8 unless it's an active fire month due to what people here are mentioning.

I think 13 is the min rating for capturing smoke particles (?)

I moved into a house running the massive 20x25x5 Lennox 6675 carbon impregnated merv 16 filter.
It's expensive, but has incredible filtering/scrubbing capability and super low pressure drop.

 

[johnmyster]

Your return air grill must be sized properly to use higher Merv filters. Too small and your evaporator will freeze up. I use Merv 13, my system was designed for them and no issue. Sams runs Filtrete on sale frequently, check online site. Amazon has good prices, sometimes they arrive damaged. Refund issued, they have improved shipping cartons, no damage lately.

In my case, the return grill houses the filter and is located in a place where I can't expand the ductwork. I got a "larger" and higher flowing filter (less pressure drop) by adapting the housing for a 4" deep pleat, as opposed to the 1" deep pleat. This increase in effective filter face area offset the move to tighter filtration media.

If I ever replace the system, we can reuse the ductwork (which is only a little undersized) but then place a larger rack for larger filters at the air handler and accomplish a similar outcome.

 

[mattwithcats]

Aldi has air filters for $6.99 this week…

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