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ellunchboxo
New Orleans Saints Fan
Gtown
Member since Feb 2009
16975 posts
 Online 

HVAC Filter question
I have 3 HVAC systems in my house and they each have a whole house air cleaner on the air handlers. The filters are 20x25x4.

Like this:



I also have filters in all the returns. My question is do I need to keep the air cleaner filters in there or can i leave them out? Or vise versa with the return filters. Do I need both, because those big filters are expensive but you don't have to change them as frequently.

TIA


LSUtigerME
LSU Fan
Walker, LA
Member since Oct 2012
2158 posts

re: HVAC Filter question
One or the other, not both.

Most people with the large filters prefer to keep them. However, there’s also some people who recommend going with the least possible restriction in the return air system by using a spun fiberglass cheapo filter.


lsuwins3
LSU Fan
Member since Nov 2008
781 posts

re: HVAC Filter question
I asked the same question before, definitely want to keep the larger one then follow manufacturers recommendation which you can probably find online. Some units may not need both may make the unit work less efficient.


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ellunchboxo
New Orleans Saints Fan
Gtown
Member since Feb 2009
16975 posts
 Online 

re: HVAC Filter question
Ok. Thanks.

We’ve been in the house a year and a half and haven’t had any issues yet. I was trying to get some perspective before spending money on those big filters.


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CrawDude
LSU Fan
Baton Rouge
Member since Apr 2019
905 posts

re: HVAC Filter question
Not a HVAC professional but have done extensive reading on the subject from HVAC sites and gathering opinions of HVAC techs, and I’m not sure that even HVAC professionals would have common agreement with an appropriate answer.

First and foremost the primary purpose of the filter is protection of the HVAC equipment and not air equality for human health. With your set up as is, probably the best answer I heard from a individual with knowledge of HVAC systems, would be to use a cheap “see through” spun fiberglass filter (not a pleated filter) in your return vent grill changed monthly, at least during the summer, and change your thicker pleated filters at 6 month intervals. You don’t want to restrict the air flow so much that it raises the static pressure in the system causing issues with air flow and having the long term consequence of reducing the life of your HVAC equipment associated with high static pressure.



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LEASTBAY
LSU Fan
Member since Aug 2007
6127 posts

re: HVAC Filter question
I had that at my old house. I think you're saying there's a smaller filter that goes before the large one correct? I would use both. You can change the small one monthly. If you just use the large one it's gonna block up with dust faster and you'll have to change it sooner.


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gumbo2176
Member since May 2018
4537 posts

re: HVAC Filter question
Here's some food for thought. You can buy permanent filters that can be hosed out monthly or whenever you would change out your filters in the return air grill.

They do cost more up front, but last for years if you don't bang them around. I ordered 2 for where my wife works when they first opened the office in an old building that was refurbished.

One cost $75 and the other cost $50 to fit the units they had installed. Once a month I'll pull them out and just hose them with the garden hose and let them drip dry and replace them in the grill. You will save money in the long run doing this.


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notsince98
Missouri Fan
KC, MO
Member since Oct 2012
10907 posts

re: HVAC Filter question
Do not use filters at the return grills. The filters at the AHU do a much better job, especially 4"-5" deep filters.

Doubling up will only kill your AHUs.
This post was edited on 10/7 at 12:20 pm


Clint Torres
New Orleans Pelicans Fan
Member since Oct 2011
1719 posts

re: HVAC Filter question
quote:

Do not use filters at the return grills.


Really? That advice sounds unusual. Where you do you get AHU filters?


CrawDude
LSU Fan
Baton Rouge
Member since Apr 2019
905 posts

re: HVAC Filter question
quote:

Really? That advice sounds unusual. Where you do you get AHU filters?

Does your air handler have a slot for AHU filter? Not all do - mine doesn’t. If that’s the case you need one at the return vent grill - assuming that how your HVAC is set up.


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20
SSpaniel
Memphis Fan
Germantown
Member since Feb 2013
18437 posts
 Online 

re: HVAC Filter question
quote:

That advice sounds unusual.


My return vents are screwed into the wall. There's not even a place to put a filter. The filter is between the return air plenum and the coil. I actually thought all were like this.


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notsince98
Missouri Fan
KC, MO
Member since Oct 2012
10907 posts

re: HVAC Filter question
quote:

Really? That advice sounds unusual. Where you do you get AHU filters?


AHU filters are essentially the same but they are located at the AHU instead of return grills.

AHU filters are much better when you have 4" to 5" deep filters like the picture in the original post. They filter more contaminants, have lower pressure drop and last longer. Their housings also tend to seal much better where as return grill filters let a lot of unfiltered air by.


baldona
Auburn Fan
Florida
Member since Feb 2016
10472 posts

re: HVAC Filter question
The primary use of air filters is to prevent your inside unit coils from getting dirty. In order to do this most manufacturers recommend 1 sq ft of filter per tonnage of air handler. So 5 sq ft for a 5 ton for your basic filter. Anything above basic needs more sq ft.

Anything above and beyond that, is all for your own air quality needs.

Just remember that there are better methods of cleaning your indoor air then HVAC air filters.


notsince98
Missouri Fan
KC, MO
Member since Oct 2012
10907 posts

re: HVAC Filter question
quote:


Just remember that there are better methods of cleaning your indoor air then HVAC air filters.


That is subjective and depends on how you prioritize the properties.

Just remember that clean rooms at hospitals, pharma manufacturing, etc. anywhere that highly clean air is required, the best and most cost effective way is through pleated media filters.


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