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Old 01-17-2010, 09:06 PM   #1
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Filter Sizing - Surface Area


My 5 Ton AH, currently has a 20x25x4 filter.

It also contributes to a high WC on the return side.

I dont know how to calculate the increased surface area of going to a 20x25x5 or even a 20x25x6 filter and it if is worth the added cost...to give me a lower WC and higher CFM?

I installed this size based on the recommendation of a couple of you HVAC guys here....I think I need to go bigger.

HVAC - Airflow Issue

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Old 01-17-2010, 09:39 PM   #2
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Filter Sizing - Surface Area


Are you using OEM refills. Or third party refills.

3 party refills are often much more restrictive then OEM refills. .1" or more.

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Old 01-17-2010, 09:54 PM   #3
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Filter Sizing - Surface Area


I believe in the "you get what you pay for" when it comes to filters.

So I use, OEM.

Currently, I have in there 3m Filtrete filter.

When I pull it, even 1/2 the way out, I can hear a difference in the air flow through the system.
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Old 01-17-2010, 10:05 PM   #4
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Filter Sizing - Surface Area


Honeywell 4" MERV 12 or Lennox 5" MERV 16 both measured .02" in several systems I checked.

Did you add those basement returns yet?
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Old 01-17-2010, 10:22 PM   #5
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Quote:
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Honeywell 4" MERV 12 or Lennox 5" MERV 16 both measured .02" in several systems I checked.

Did you add those basement returns yet?

Sort of, I took the end off one one of the return trunks...its a 10x26 trunk.

So, yes.

When I use my homemade manometer...I get a higher reading when I check between the blower and filter.

When I check above the filter, the reading is neglible. So I think the capacity thru the ductwork is ok.
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Old 01-17-2010, 10:39 PM   #6
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Wouldnt I be fine with say a merv 6-8 for winter (heating) season and then bump back up to a higher merv in the summer?

I have no problems cooling the house, its heating....that is the challenge.
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Old 01-17-2010, 11:35 PM   #7
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3M filtrete is one of the worse you can use. they are very restrictive.
Use a Honeywell of the same MERV, and you'll get much better air flow.

You don't need more then a MERV 8.
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Old 01-18-2010, 07:33 AM   #8
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3M filtrete is one of the worse you can use. they are very restrictive.
Use a Honeywell of the same MERV, and you'll get much better air flow.

You don't need more then a MERV 8.
Good to know. My lowes only carried this filter in a 4" thick, which is what I needed baesd on your previous suggestions.

I'll order some honeywell filters today online...if I upsize to a 5" or 6" thick, that should help with the WC too, right?

Or is there a point of no value(return) when going "thicker"?
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Old 01-18-2010, 07:38 AM   #9
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A 5 or 6" should reduce your wc. But, I'd try one of the Honeywell 4" first.
You may not need to go bigger if you use them. And, I can't say that a 5 or 6" would have enough of a lower PD to get you a noticeable change in air flow.

A HW 4" will probably have a .1 plus lower PD across it then that Filtrete.
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Old 01-18-2010, 01:03 PM   #10
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A 5 or 6" should reduce your wc. But, I'd try one of the Honeywell 4" first.
You may not need to go bigger if you use them. And, I can't say that a 5 or 6" would have enough of a lower PD to get you a noticeable change in air flow.

A HW 4" will probably have a .1 plus lower PD across it then that Filtrete.
That is a significant drop in WC, right?

I dont mind going to a 5" if it has a remote chance of being even better, especially when the filter loads up.
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Old 01-18-2010, 02:53 PM   #11
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A 5" will have a longer time before it restricts as much as a 4". And may be worthwhile.

That i can say from this monitor.
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Old 01-18-2010, 07:52 PM   #12
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What are the thoughts on a filter loading gauge?
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Old 01-18-2010, 09:53 PM   #13
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As often as your in your basement. Its a good thing.

Most people don't check them. But I believe you would be an exception to that rule.
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Old 01-18-2010, 11:22 PM   #14
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As often as your in your basement. Its a good thing.

Most people don't check them. But I believe you would be an exception to that rule.
Hmmh, which way to take that remark.

I check my basement almost everyday....even though it is not a finished basement, we do store things down there...and the sump pump failed last Christmas Eve.

The way I knew the basement was flooded (4" water) was because one of my furnace monitor probes had failed, it was under water.

I saw that item on a website I was ordering the filters from. I didnt buy it...seems to me, I'd likely be replacing the filter regardless of what that device said to do.

You familar with this companies filters?

http://www.glasfloss.com/utils/file.cgi/zspf.pdf
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Old 01-18-2010, 11:35 PM   #15
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LOL... It was a compliment.

I use those on some commercial apps that nee good filtering, and have routine maintainence done.


The 20X25X4 HV is ok. The SB and ZL are too high of a PD. And the nice thing is with those PDs, they are rating at 500 FPM.

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