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Old 12-25-2008, 05:20 PM   #16
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Furnace Filters


Thanks for your data. I will save it to compare to my 4-3/8 inch filter by 16 X 25 inches. I suppose that to measure properly, I would need to test two times; once with the filter in place and once without. I am glad that "beenthere" answered this thread because there's a lot of people that do not know about the differant pressure drops between OEM and third paty filters even of the same material and size.

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Old 12-26-2008, 05:16 PM   #17
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I decided to do a performance test to check out both low and high heat for static pressure and pressure drop with a 4-3/8 X 16 X 25 inch 3M filtrete high performance filter. The filter was in use for 23 days before the test.

Low Heat, 0.29 static pressure with the filter in place.
High Heat, 0.58 static pressure with the filter in place.

Low Heat, 0.17 static pressure with the filter removed.
High Heat, 0.37 static pressure with the filter removed.

The pressure drop on Low Heat is 0.12
The pressure drop on High Heat is 0.21

This filter has a merv rating of 12 whereas the OEM has a rating of 8. Right away, this tells me that with a merv of 8, I should see a lower static pressure and a lower pressure drop.
And with a high heat static pressure of 0.58, I am under the recommended range of 0.8 per message #10.

I'll be running this test monthly to see how the numbers change. It does appear that the present filter is ok for now.

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Old 12-27-2008, 04:32 AM   #18
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When its time to change out that filter.
Try an OEM MERV 13 and see what your PD is.
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Old 12-27-2008, 06:29 AM   #19
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I will do that but it will take a year or more before I use up my filters. I have two Bryant filters on order. I looked over the installation manuals and owners manual and could not find any mention of what type of motor runs the blower. You mentioned ECM and I did not see this term. Do I need to remove the blower cover door to check the motor label? I have the model 315AAV/JAV Bryant plus 80 furnace.

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Old 12-27-2008, 06:39 AM   #20
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The Bryant 315AAV is an 80% AFUE VS/ECM blower furnace.
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Old 12-27-2008, 06:47 AM   #21
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Thanks.
While I was testing the performance, I also checked to see the pressure drop when I closed off the two returns in the basement with the filter in place and it went up to o.66. A big jump from 0.58 when they are left opened.
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Old 12-27-2008, 06:55 AM   #22
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If you redo that test.

Listen carefully, and you will hear the blower speed up, to maintain set air flow CFM.
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Old 12-27-2008, 07:02 AM   #23
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This has turned out to be an interesting thread for those interested in improving the performance and economic capabilities of their furnaces. Now it also has given me another thing to check in the cooling season. I have both bottom and top returns installed and I been closing the bottoms when using air conditioning. Now I wonder if that is raising the static pressure and causing the blower to be less efficient economically.
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Old 12-27-2008, 10:27 AM   #24
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Do you have the high ones closed off now.
If so, open them and see if your static drops.

I tell most people to leave both open weather heating or cooling.
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Old 12-27-2008, 10:44 AM   #25
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Thats interesting.
I thought the idea was to maintain efficiency by using upper returns during the cooling season and lower returns during the heating season. I never tried leaving both opened during the heating season. I will open all upper returns, after I get back from shopping to see effect on sp. The basement returns are in a high location. I did not install low returns there. The rest of my two story home has both upper and lower returns and discharges. I know that if I opened all the upper and lower discharges for cooling on the first floor, it does affect the cfm output to the second floor. So I think doing this for the heating season may affect it just as well.
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Old 12-27-2008, 10:51 AM   #26
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If you only open the lower returns in heating.
The the warmest air will stay at the ceiling, and the coldest at the floor.

Open both the high and low returns. You don't really need your ceiling to be 2 to 6 warmer then your floor do you.
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Old 12-27-2008, 11:00 AM   #27
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Thats right.
I never thought of it that way. I'll open them up now and go shopping. When I get back, I'll test again to see if sp was improved.
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Old 12-27-2008, 01:43 PM   #28
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With both top and bottom returns opened and the furnace heat on low, sp was the same as before, 0.29.
with the furnace heat on high, sp moved up a bit to 0.60. I did notice that the rpm's did increase slightly also.
So I guess I can dismiss this test and see what result I get when the cooling season starts.
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Old 12-27-2008, 04:25 PM   #29
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Strange that it went up.
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Old 12-27-2008, 06:54 PM   #30
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I believe it may have something to do with moisture in the air and the physics of air movement under changing conditions. The only thing I did was to leave the blower on low speed for over two hours before I tested. I normally leave it on auto during the heating season because I do feel cool air coming out of the discharge long before the heat kicks on. Both low and high heat tests last 5 minutes and I take my readings at midstream.

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