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Old 08-18-2020, 07:02 AM   #1
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MERV rating of filters- is what I did ok ?


In December I had a 18 SEER dual fuel system installed in the house . The system uses a 16" x 20" x 4 " filter . I decided to replace it but couldn't find one locally so I purchased four 1 " thick filters . The existing filter had no MERV rating stamped on it . I called the installer and he said if you can't see through it then it's good enough , gotta love good ole boy humor

So I went to local big box store and purchased two filters rated MERV 4 and two filters rated MERV 7 . The four individual filters fit the housing as well as the original 4 " thick filter . I did this a week ago and no visible signs of any issues . Very hot/humid where we live but the system seems to be working great .

So any issues you guys see with using the individual filters ? I am thinking in 3 months pull the leading filter out , move the remaining 3 to the front of the line and back fill with one new filter . And keep doing this every 3 months . Any new filter will be of the same MERV rating as the one being pulled out of rotation .

I of course can just order online the 4 " filter to get the cost down and I can do the same for the 1 " filters . But it is handy to be able to buy the 1 " locally in a pinch and they aren't that expensive .
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Old 08-18-2020, 08:17 AM   #2
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Re: MERV rating of filters- is what I did ok ?


No, too restrictive using stacked 1” filters.
The 4” are superior for flow. Just order 2 and always have 1 as a backup.
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Old 08-18-2020, 09:45 AM   #3
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Re: MERV rating of filters- is what I did ok ?


Bad idea. Restrictions are additive so you had the practical equivalent of a Merv 22 filter. Very restrictive!

Furnace manufacturers recommend no higher than a 7 Merv filter for their own selfish reasons during the warranty period but it works for your protection after that since replacing a damaged heat exchanger is an expensive process.

A convincing demonstration would be to have the blower running without any filters installed and to install your filters one at a time. You will quickly notice that they get pulled in less strongly as they get stacked in there.
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Old 08-18-2020, 12:37 PM   #4
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Re: MERV rating of filters- is what I did ok ?


I'll pile on and add a suggestion...

For sure this is bad, don't even wait for those filters to be spent, If you can't find the correct filter you need at a local retailer, just order online.
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Old 08-18-2020, 05:18 PM   #5
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Re: MERV rating of filters- is what I did ok ?


You can get the correct filters on Amazon or Smarthome. Take those 1" filters out until the 4" one comes in.

Note - 4x1" filters is not the same as 1x4" filter, not by a long way. A 1" filter has ~4x the resistance as a 4" filter and 4 of them have ~16x the resistance of a 4" filter!
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Old 08-19-2020, 12:23 AM   #6
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Re: MERV rating of filters- is what I did ok ?


Our FL house has an unusual filter size. I order from an Amazon vendor and get high quality filters.
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Old 08-19-2020, 06:23 AM   #7
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Re: MERV rating of filters- is what I did ok ?


Appreciate the feedback/advice I will order 4 " thick filters .
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Old 08-19-2020, 09:44 AM   #8
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Re: MERV rating of filters- is what I did ok ?


Now you're cookin'

Although the bulk of the information in this thread (my part included) is somewhat exaggerated to get your attention, the intentions were noble enough and the outcome is proper.

Actually the restrictive effects of using multiple filters is additive but not at a linear rate. Since MERV values were established by ASRAE, they used an arbitrary flow rate for their standard *. With that comes the rule of diminishing returns/effects when you start reducing the air flow on a system.

Best regards, SD2

*For the curious that may be interested in digging deeper into this, I recommend the following MERV rating explanation compiled by a P.E.:
+
+ https://web.archive.org/web/20150412...xplanation.pdf
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Old 08-19-2020, 09:48 AM   #9
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Re: MERV rating of filters- is what I did ok ?


Quote:
Originally Posted by Porsche986S View Post
Appreciate the feedback/advice I will order 4 " thick filters .
A very wise choice.
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Old 08-19-2020, 11:53 AM   #10
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Re: MERV rating of filters- is what I did ok ?


I ordered a twin pack of filters with a MERV rating of 8 . Visually they look just like the one I pulled out . They will arrive on Monday per the tracking .
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Old 08-20-2020, 09:16 AM   #11
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Re: MERV rating of filters- is what I did ok ?


Lastly, I put strips of painter's blue tape on filter edges to frame. Then put the date on that.
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