HVAC Filters

About seven years ago, my heat exchanger cracked on my not too old furnace which was under warranty. The technician said it probably happened from lack of air flow through the high merv filter I was using. He suggested using the cheap glass wool ones for better air flow.
 
That is epic! I looked up the FC40R (8 MERV though, but this is sufficient in my opinion), and it has a 0.12 pressure drop per 2cfm per sq in. At 1000cfm, that is 0.12 for my application (20x25). Compared to the 3M filter I have, which is their best 1" filter for drop, it offers 0.15 pressure drop at 1000cfm.

This is initial, only, however. I am sure the loading curve for the thicker filter is much more generous.

So now the question is...0.12 vs 0.15 isn't really that big of a deal...is it worth it to me to deal with ordering these special if I cannot buy them local (Doubtful), or should I just change my 3M every month or two as usual for similar performance at 13 MERV > 8 MERV?

I honestly think the details won't matter much, here, but if I can buy the one you linked to local, I certainly will, instead. Do you know of a chain that sells them?

I have been subscribing to these 5” filters at Filter Buy having them delivered every 6 months. Works great. I use the 24” x 30” x 5” MERV 11.
 
When we had are new furnice installed about 10 years ago the guy gave us a couple boxes of filters and told us once a year. They are 20x25x4 MERV 7. So when we needed new ones that is what I got how ever we change them at six months due to having pets, they just look to nasty to go longer. We also had a UV light installed or it came with one.
 
I purchased the Filterbuy 5" deep MERV 11 filter with the "adapter" border around it for my 1" grill. Fits better than 1" filters do! AWESOME! I messaged them and they said the MERV 11 has a 0.22 pressure drop at just under 2000cfm!!! $35/3 month delivery schedule is what I bought, which should be around right I think to keep things in peak condition! Glad I started this thread! Thank-you!
 
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About seven years ago, my heat exchanger cracked on my not too old furnace which was under warranty. The technician said it probably happened from lack of air flow through the high merv filter I was using. He suggested using the cheap glass wool ones for better air flow.
Biggest threat to heat exchangers is inadequate return air. I haven’t checked IMC recently but code was 2 sq inches min. Per 1000 btu input.
 
I went down a bit of a rabbit hole today. Many HVAC techs I know and trust (friends and family, some with 60-70+ years in this field!), have always told me a MERV 5-7 cheap pleated filter was the way to go. The hog-hair filters let too much dust hit the coils of the HVAC system, and the MERV 13's provide so much backpressure you can have issues. However, I always try to do my own research, as well. It led me to this, which I have found very interesting, and will change how I buy filters.


TL/DR: Merv 13 Filtrete 1900 filters provide less backpressure than MERV 5 Basic and lesser filtering filters in many cases. Wild! Also, Filtrete factory flow ratings were typically PESSEMISTIC vs. actual lab data from 3rd party. A manufacturer who sells their product short...WOW!

My purchasing habit has altered, and I will now use the 3M Filtrete MERV 13 "1900" series filters, as my system is a 20x25x1"
Previously, I used a MERV 8-10 Filter / kind of mid range.
Today I cleaned the cold-air returns (as best I could).
Before cleaning, I installed the Filtrete 1900 / to better collect any dirt I loosened up.
It collected quite abit of dirt.
Now the question is "how long can I use this filter, before the differential pressure is to great?"
I installed an Inclined Manometer to show me exactly the pressure difference.
To me, using a Manometer (differential pressure gage) is essential in not over-working the blower motor.
Any filter, any MERV, any thickness, .... I read the gage / other then that, you're guessing how long to use the filter

The furnace manufacturer shows .50 inch max. of water column.
I plan on using any filter to a max of .40"wc / gives me a little wiggle room.

When I installed the Filtrete 1900, the gage showed .27"wc
The less restrictive filters (1085) have a 'higher' gage reading of .30"wc

WHY? .... because the 1900 filter has 48 pleats, vs 19 pleats / it's a bigger filter.
NOW, .... the question is, "how long will the filter last till the gage reads .40"

Ideal situation for me is the 1900 lasts 8-9 Months.
If only 2 Months, I would have to use a less restrictive filter, or have my furnace reworked to fit a 5" thick filter.

Another important thing to do is, clean your floors (more often) so the cold air returns are not sucking up excess dust.
I do not believe in using the furnace filter as an air cleaner, but I also don't want all that dust in the duct work.

Photo of my Differential Gages.
I like the 'red' liquid one most / dial one is for double checking, if needed
IMG_20220223_123412540.jpg

If anyone wants to buy the liquid Manometer, they are expensive, like $500.
I was lucky to get one on E-Bay for way cheaper.

Untitled.png
 
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About seven years ago, my heat exchanger cracked on my not too old furnace which was under warranty. The technician said it probably happened from lack of air flow through the high merv filter I was using. He suggested using the cheap glass wool ones for better air flow.
YUP.... I use a filter of MERV 4 or less....
 
Previously, I used a MERV 8-10 Filter / kind of mid range.
Today I cleaned the cold-air returns (as best I could).
Before cleaning, I installed the Filtrete 1900 / to better collect any dirt I loosened up.
It collected quite abit of dirt.
Now the question is "how long can I use this filter, before the differential pressure is to great?"
I installed an Inclined Manometer to show me exactly the pressure difference.
To me, using a Manometer (differential pressure gage) is essential in not over-working the blower motor.
Any filter, any MERV, any thickness, .... I read the gage / other then that, you're guessing how long to use the filter

The furnace manufacturer shows .50 inch max. of water column.
I plan on using any filter to a max of .40"wc / gives me a little wiggle room.

When I installed the Filtrete 1900, the gage showed .27"wc
The less restrictive filters (1085) have a 'higher' gage reading of .30"wc

WHY? .... because the 1900 filter has 48 pleats, vs 19 pleats / it's a bigger filter.
NOW, .... the question is, "how long will the filter last till the gage reads .40"

Ideal situation for me is the 1900 lasts 8-9 Months.
If only 2 Months, I would have to use a less restrictive filter, or have my furnace reworked to fit a 5" thick filter.
Sweet, yeah the starting dP of most of the filtrete filters are not that different.
How quickly that dP builds is the important question. Report back let us know how it goes.
 
Previously, I used a MERV 8-10 Filter / kind of mid range.
Today I cleaned the cold-air returns (as best I could).
Before cleaning, I installed the Filtrete 1900 / to better collect any dirt I loosened up.
It collected quite abit of dirt.
Now the question is "how long can I use this filter, before the differential pressure is to great?"
I installed an Inclined Manometer to show me exactly the pressure difference.
To me, using a Manometer (differential pressure gage) is essential in not over-working the blower motor.
Any filter, any MERV, any thickness, .... I read the gage / other then that, you're guessing how long to use the filter

The furnace manufacturer shows .50 inch max. of water column.
I plan on using any filter to a max of .40"wc / gives me a little wiggle room.

When I installed the Filtrete 1900, the gage showed .27"wc
The less restrictive filters (1085) have a 'higher' gage reading of .30"wc

WHY? .... because the 1900 filter has 48 pleats, vs 19 pleats / it's a bigger filter.
NOW, .... the question is, "how long will the filter last till the gage reads .40"

Ideal situation for me is the 1900 lasts 8-9 Months.
If only 2 Months, I would have to use a less restrictive filter, or have my furnace reworked to fit a 5" thick filter.

Another important thing to do is, clean your floors (more often) so the cold air returns are not sucking up excess dust.
I do not believe in using the furnace filter as an air cleaner, but I also don't want all that dust in the duct work.

Photo of my Differential Gages.
I like the 'red' liquid one most / dial one is for double checking, if needed
View attachment 91485

If anyone wants to buy the liquid Manometer, they are expensive, like $500.
I was lucky to get one on E-Bay for way cheaper.

View attachment 91487
Wow! Awesome post, I love facts and figures.
Yeah, air filters is more like black magic, anything goes nothing based on science because not enough people have instrumentation like you bought and for some reason hard to find actual publications that do what you do, with the name of the brand of filter.
We use Merv 8 to 11, best price wins but we do something a bit different. Not sure if you are aware based on your post.

We have 4 air returns two on the main level for one unit and two on the second level for the other.
Our system uses 2- 20x20 filters and 2- 14x14
Typically almost everyone uses 20x20x1 and 14X14X1 in the air return grill. However I was concerned about getting max air flow and some of the air registers in my house have to kick air down up to 10 feet when heating the house, of course we know cold air sinks so not an issue there.

Anyway, MANY years ago I started using 5 inch thick return grill filters. 20x20x5 and 14x14x5 they fit right into the air return grills. I only use them on the first floor as the first floor gets a lot more use and also I guess dirt settles to the lower level because the 1 inch get dirty fast. 5 inch (actual 4 ish inches) arent cheap but they last a lot longer between needing to get changed. Like you state that is where there is no science to change them.

I thought about buying a deal in Costco, they were 2200 Filtrite but the cost was low enough where if I changed them out every 3 months it would cost almost the same as one of the 5 inch filters per year is what I have been changing them out on the main level but this year think I have decided to go 6 months using the Merv 11 now.
Anyway, it drives me nuts not being able to see actual measurements on what air flow loss is or pressure as you measure and makes me nervous to buy a 2200 filter, I still remember the builder saying to use the $1 cheapest fiberglass filter. That is why, not wanting to use the unrestricted cheap fiberglass I went to the 5 inch thick in the hopes of surface area making up for the higher Merv.
I actually prefer Merv 8 but in the case of the photos, the 11 was only $2.50 more so went with the 11.
I suspect you do not have return grill filters and why the mention of would need reworking.

IMG_6772.jpg
 
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I think ever house is different.
What works for me, may not work for others.
How quickly a filter loads up causing larger pressure difference is determined by:
* Number of people living in the house
* Any cats or dogs
* Burn candles
* Heat with wood
* Return ducts of inproper size (to small)
* Fan speed / higher rpm will increase pressure on gage
Only real way to tell what your system is doing is with a differential pressure gage.
If I'm wrong, tell me why.

A less expensive pressure gage:
 
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Well, I have come to the conclusion that I need to get my furnace fitted to use a 4" or 5" filter.
Using 4"-5", data shows that the pressure drop is very low / my gages may not be needed if I change the filter yearly.

I may even save some money because the 1" MERV 13 are expensive.
 
I gave the Filtrete 1500's a go on my heat pump system and it was a no go. The 20x20 Filtrete's were very tight and barely fit without some maneuvering and warping of the cardboard frame, also after ~3 months (my Nest usually calls for filter change every 6 months or so) my air handler was screaming at me (its in the ceiling above the shower) which only settled down after changing back to the freebies from the HVAC company.

The PM contract with the company who installed my unit gives me nice pleated filters that are MERV 8 (Aerostar Nova pleated) and they have worked well and my air handler is not screaming by the time the Nest determines its time for a change. I did a little upgrade to the filter housing and added some rubber weatherstripping so the filter should suck itself up against the rubber strips when the system is on to keep dust from sneaking around the edges.
 
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