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Old 08-01-2020, 12:27 PM   #1
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Filter differential pressure


Being an ex Navy guy and having worked in the nuclear industry this is one of those things I have wanted to do for a long time. We of course had lots of air filters and they were always monitored for D/P to check performance and to indicate replacement. So I got a Magnehelic gauge and installed the probe tips on either side of my filter. This is a 16X25X1" filter, system has an ECM fan air handler (York TM9V) in cooling mode with a 3 ton Bryant condenser, with air handler jumpers set to 1200 CFM.

I have always used the pleated filters and wondered how high the D/P would be. Turns out pretty high. The photo below is running a brand new MERV 8 filter. I'll operate it like this and monitor performance and see how much and fast the D/P rises over time, and eventually decide on replacement criteria. D/P numbers will obviously be a little less in heating mode where the airflow is lower, especially in low fire.

This is one of those "unnecessary" projects you do when you are retired and in pandemic mode, I guess.
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Old 08-01-2020, 12:37 PM   #2
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Re: Filter differential pressure


It would be interesting to determine what the D/P would with a cheeeeep 1" fiberglass.



I could check mine but i have two 15x24 filters servicing a 2.5 ton unit and my home made manometer wouldn't even be close to your equipment capabilities.




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Old 08-01-2020, 12:39 PM   #3
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Re: Filter differential pressure


Probably very close to the zero it reads with no filter. But those let too much crap get through to clog up the coil.

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It would be interesting to determine what the D/P would with a cheeeeep 1" fiberglass.



I could check mine but i have two 15x24 filters servicing a 2.5 ton unit and my home made manometer wouldn't even be close to your equipment capabilities.




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Old 08-01-2020, 01:40 PM   #4
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Re: Filter differential pressure


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Probably very close to the zero it reads with no filter. But those let too much crap get through to clog up the coil.
My fiberglass don't seem to let crap through. Wanna see the blower wheel that's never been cleaned after 36 years. Oh, i about forgot the F/G filters have had the same washable hog hair pre filters for the last 10 or 15 years. The tech nor i have ever looked at the coil and tech said there's no need to look with a wheel that looks like that and a DT of 20 on a good day and 16 on a bad day.




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Old 08-01-2020, 02:33 PM   #5
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Re: Filter differential pressure


You must be doing some clean livin'! ;-)


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My fiberglass don't seem to let crap through. Wanna see the blower wheel that's never been cleaned after 36 years. Oh, i about forgot the F/G filters have had the same washable hog hair pre filters for the last 10 or 15 years. The tech nor i have ever looked at the coil and tech said there's no need to look with a wheel that looks like that and a DT of 20 on a good day and 16 on a bad day.




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Old 08-01-2020, 04:57 PM   #6
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Re: Filter differential pressure


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You must be doing some clean livin'! ;-)
Thanks, but really not any different than average i suspect. Maybe some different that the 3 kids have been away in their homes for maybe, well i don't really know how long, but awhile.




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Old 09-01-2020, 06:07 AM   #7
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Re: Filter differential pressure


Some of you may recall I installed a Magnehelic differential pressure gauge across the 16x25x1 filter in my York TM9V furnace air handler with 17" cabinet. Furnace is an 80kBTU 96% efficient. A/C condenser is my old Bryant 3 ton R22 unit.

I have always used the mid to lower MERV or FPR pleated filters first in the original Bryant furnace/air handler with PSC blower and then with the York with its ECM blower. Never had any problems but after all the discussions here about how restrictive they can be I had to test it.

I ran my usual MERV 8 filter for a month and it worked OK, as expected. D/P started out at about .25" and ended up about .28". Filter didn't look too dirty and I could have run it another month but the experiment couldn't wait.

So today I picked up a 3 pack of Rheem MERV 4 filters at Home Depot... and one Honeywell MERV 12. I fully expected the higher MERV filter to be more restrictive but I thought that the additional pleats created more overall surface area and that might mitigate some of the rise. But the question was, how much? Turns out not so much after all. The Rheem MERV 4 produced a differential pressure of about .15". But the MERV 12 Honeywell produced a whopping .4"! Yikes. And I could hear the blower motor adjust to try to compensate for it. It was working hard. So, no way I'll be using that MERV 12 filter. Wasted a few $ but I had to know.

These all in cooling mode with the jumpers set for 1200 CFM.


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Last edited by raylo32; 09-01-2020 at 06:11 AM.
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