Any links to studies on MERV rating effectivenss?

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Old 10-17-13, 06:52 AM
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Any links to studies on MERV rating effectivenss?

Folks:

My new Lennox Elite Series EL296U two-Stage gas furnace was installed yesterday. So far, so good. My question to the group is regarding filters. It was put in with a large and properly built return system that utilizes a 25X29X4 filter. I thought I'd get a few on hand and noticed there are many different MERV rated filters. I generally know what that different level means. Has anyone done a MERV "restriction" test? Meaning if I go higher up the MERV scale, do I get reduce air flow? Thus, is there a good balance between filtration and flow? These filters are not cheap; I want to get the right one going forward.

Love your thoughts on the matter...thanks in advance!

TKH
 
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Old 10-17-13, 07:31 PM
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I can't point you to any published studies but can tell you from many years in the trade that yes, air flow does decrease as MERV increases. I can't begin to tell you how many frozen A/C coil calls I've been on which were directly traceable to high MERV filters.
 
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Old 10-18-13, 07:19 AM
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Grady:

That's what my logic would tell me, so I agree with you. If you decrease the size of items that can make it though, you've got to restrict something (flow).

Considering I only want to protect my fan motor and A/C coils from getting dirty, MERV 8 should be more than adequate. If I was running a clean room and producing medical equipment or silicone chips, etc, I would want the highest possible. However, to protect my furnace and keep my interior coils clean, MERV 8 sounds like more than sufficient given all the junk we (as humans) deal with day in and day out.

In your experience, if someone has a well designed return system where the filter is in a sealed box that requires all flow to pass through it--and the filter space is for the 4 inch pleated filters--have you seen situations where A/C coils do NOT need regular interior cleaning? My installers said if you keep these large, high-quality filters in place and change them as needed, you shouldn't have to clean the inside nor outside of your A/C coils.
 
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Old 10-18-13, 04:30 PM
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Your installers are trying to sell you a high dollar filter.
All I use in mine is the 1" glass fiber filters & change them as needed. By needed I don't mean any specific time interval but when the get dirty. My system has been in 23 years & I finally cleaned the coil this year & it wasn't bad at all.
 
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Old 10-18-13, 04:52 PM
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I had a standard split unit back in VA and used the cheap blue (<$1 each) then the cheap pleated (about $6 for 3) after my step-son with allergies came there. Changed as needed based on system usage. 3 cats, carpeted throughout. When we sold after 16 yrs the inspector asked if I had had recent service since the inside and outside coils were so clean. I said, "Nope, that was just me changing the filters regularly and hosing out the outside unit once a year'.

The 4" filters (from what I understand) will last a long time and not reduce flow as much. I've even seen recommendations to just inspect and replace as needed at the start of each season. They ARE harder to tell if they are really dirty though. So if you replace it every 6 months or so, how much will that cost?

The very best way is to have a gauge that tells you when flow across the filter is being reduced. Seems I used to see that as an option on installs way back when.
 
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