HVAC Filters

Ws6

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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"
 
I have tried all the efficient filtrete filters, and many dupont ones as well, in size 16×25×. With my system, all but the lowest merv rating restrict airflow too much. It may just be my particular case and size, but merv 3 from true blue, yes the cheapo filters, are what works for me. I prefer airflow over filtration as I feel it stresses my system too much. If I want to purify the air, I will turn on my air purifier.
 
I have tried all the efficient filtrete filters, and many dupont ones as well, in size 16×25×. With my system, all but the lowest merv rating restrict airflow too much. It may just be my particular case and size, but merv 3 from true blue, yes the cheapo filters, are what works for me. I prefer airflow over filtration as I feel it stresses my system too much. If I want to purify the air, I will turn on my air purifier.
What is odd is that I am looking at lab tests showing the MERV13 filters retard airflow the least except for some of the MERV 1 stuff, which can easily allow damage to coils.
 
It is odd. I would hope there are other tests to corroborate that information. Until then, my own experience will have to suffice but I do have a filtrete 2200 to give a shot again. It is merv 10 I think. Again, I think my smaller duct work may have a limitation on the merv rating I can run in most cases.
 
It is odd. I would hope there are other tests to corroborate that information. Until then, my own experience will have to suffice but I do have a filtrete 2200 to give a shot again. It is merv 10 I think. Again, I think my smaller duct work may have a limitation on the merv rating I can run in most cases.
This test in my OP was performed by the state of CA, not a dude in his basement. Let's leave politics out of it for a minute, I trust the state lab pretty well to get something like this right.

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My system was bottom shelf at the time, has degraded, and become dirty(naturally)over the past 15 years. When my merv 3 filter is at capacity, it causes suction to the vents and flexes them, making a loud popping noise. This happens with new, higher merv filters as well. I am therefore unable to corroborate directly with the testing you have provided.
 
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Seems like the Filtrete Merv13 1900 has the best balance of filtering and initial pressure drop. But I’m curious how it holds up as it gets dirty. One of the lower end filters might start a little higher initially, but maintain a lower pressure drop as it loads up.

I have absolutely no scientific data to back my personal experience up, but when my son was diagnosed with asthma I immediately switched to the higher end 1900 or 2200 (it’s been a few years) to help him out. After 2 months the filter was starting to bow in from the suction created by the HVAC unit, something I never noticed with the lower end filters. Although my unit... and the new one, both use 14x20x1 filters.
 
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If you want to increase the amount of filtration you can reduce the pressure drop by increasing the area of the filter. For example if your furnace takes a 20x30 then you could build a return air box that holds 2 filters turning it into a 40x30. I've seen one photo of a building science/HVAC guy who turned the closet door to his furnace into one huge filter. I think he used something like 4 - 24x12's placed edge to edge.
 
I've been using the Merv 13 Filtrete filters on my system. 2003 Trane XR12. I use the 20x25x1 and I don't notice any restrictions. But I have noticed a lot less dust since I switched to these filters from the cheapos. I also just installed a Honeywell UV Light in my return.
 
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I try to use at least MERV 11. Going higher costs a lot more.

I am getting the ducts cleaned next week. We have lived here 26 years with no cleaning and have always had dogs and cats.
 
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This test in my OP was performed by the state of CA, not a dude in his basement. Let's leave politics out of it for a minute, I trust the state lab pretty well to get something like this right.

This is initial pressure drop only (not loaded with dust).
They achieve lower pressure drop with better materials and more pleating.
 
So what gets installed at the coils these days ? We put our latest HVAC system on a PM contract since I travel … and they tell me it’s a pretty thick filter changed quarterly … (so far I have not been home when changed) …
We are told “rock catchers” only (glass) in the two original intake spots …
 
I have used this thicker filter for a while:
Amazon.com: FilterBuy 20x20x5 Grille Honeywell FC40R1003, FC35A1043 Compatible Pleated AC Furnace Air Filters (MERV 11, AFB Gold). 2 Pack.: Appliances

Please choose the correct size for your application, this is the 20x20x5.
Note that there is a lip to hold this filter where a 1" thick filter is used.

There is a MERV 13 also but I usually just used MERV 11.
I replaced mine once per year since it has more dust capacity, 5 inches thick instead of 1 inch.
Although, that depends on the location and usage like pets, etc.
 
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If you want good filtering you want a 5" thick media filter housing and filter. Aprilaire sells them. But it needs to be installed between duct work and HVAC air handler. So more involved than sliding a new filter in.
 
I have used this thicker filter for a while:
Amazon.com: FilterBuy 20x20x5 Grille Honeywell FC40R1003, FC35A1043 Compatible Pleated AC Furnace Air Filters (MERV 11, AFB Gold). 2 Pack.: Appliances

Please choose the correct size for your application, this is the 20x20x5.
Note that there is a lip to hold this filter where a 1" thick filter is used.

There is a MERV 13 also but I usually just used MERV 11.
I replaced mine once per year since it has more dust capacity, 5 inches thick instead of 1 inch.
Although, that depends on the location and usage like pets, etc.
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?
 
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