I have been using the cheapest pleated filter I can find, but was recently told by someone in the industry that even they are too restrictive and they recommend the el cheapo fiberglass filters. He claimed they filter well enough and are much less restrictive. Thoughts? It seems opinions vary, some pros recommend the cheap pleated filters and others recommend the fiberglass ones.
Home HVAC filters
- Thread starter dishdude
- Start date
MERV 8 or less has been my hvac pro's recommendation for the last 35 years Living in Texas the a/c runs alot.
I run at my house a 4 inch 16x25 13 merv with 1 fiberglass cheapo in front of it to "cake" most of the dirt and clean the cheapo one time in the middle of the 6 month run time.
When I bought all my stuff for my daughters new furnace/A/C/new venting. I bought her a 4 inch 20x25 filter carrier that allows the cheapo prefilter to promote "caking" I get 6 months out of mine and it appears she will too if she goes Merv 13. She will use that too because of allergies/my wife too/ but not me luckily. She has a 3D printing business with 10) 3D printers going 15 hours a day. We use 2 separate HEPA filter standalones in her printing room to clean the air of micro particles. I have a $300 micro particle counter to verify that we are getting most of the particles.
When I bought all my stuff for my daughters new furnace/A/C/new venting. I bought her a 4 inch 20x25 filter carrier that allows the cheapo prefilter to promote "caking" I get 6 months out of mine and it appears she will too if she goes Merv 13. She will use that too because of allergies/my wife too/ but not me luckily. She has a 3D printing business with 10) 3D printers going 15 hours a day. We use 2 separate HEPA filter standalones in her printing room to clean the air of micro particles. I have a $300 micro particle counter to verify that we are getting most of the particles.
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I've been running the cheapest MERV 8 I can find for many years now. When I first bought my house, I ran a higher MERV, but it seemed to restrictive. MERV 8 has been a good balance for me with allergies, price, and restrictiveness. My furnace/ac is a 25 YO Goodman system.
I use a MERV 4 or less and change every 30 days or so....
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I have been using these project source filters from LOWE'S I feel they meet the needs of good efficiency and filtering
I just get the cheap fiberglass ones and change every 30 days. There are systems like from AprilAire you can have installed that'll provide more filtration without restricting the blower motor due to the larger filter area. Talk to your local HVAC people for options.
AZjeff
$50 Site Donor 2023
HVAC (furnace) filters were originally meant only to keep dust out of the heat exchanger and blower and later the AC condenser but have evolved into actual air cleaning devices. I had a long time HVAC guy tell me that using higher MERV filters is hard on the blower motor and obviously restricts flow volume which raises utility bills. Said to use the fiberglass filters to do the job as intended and if I want an air purifier filter get a stand alone unit in the living space which we've been doing for years. This might be old school thinking but there's no doubt the higher MERV filters restrict airflow. If you research it you'll find mentions that HVAC systems manufactured in the past 20 years should be able to handle MERV 13 filters without harm. Maybe so. Also you should be able to find what filter your unit is rated for if you have the literature that came with it or look it up online.
Our 7 year old 1600 sq ft house with 10 foot ceilings has a stupidly undersized 20x20x1 return filter so I only use the fiberglass filters to maximize flow. I tried a MERV 8 and it bowed significantly inward from the restriction so went back to fiberglass. Keep thinking about changing the filter box to a 20x20x2 or even a 20x20x4 filter to get more media just haven't done it.
Our 7 year old 1600 sq ft house with 10 foot ceilings has a stupidly undersized 20x20x1 return filter so I only use the fiberglass filters to maximize flow. I tried a MERV 8 and it bowed significantly inward from the restriction so went back to fiberglass. Keep thinking about changing the filter box to a 20x20x2 or even a 20x20x4 filter to get more media just haven't done it.
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- Apr 13, 2025
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Here is what I have been told....YMMV....
Air flow determines how much water is removed from the air in your home (assuming a properly sized and efficient AC system). If the air flow is too great, too much moisture is drawn off the coils and back into the air resulting in higher humidity.
Not enough air flow and the coils can freeze condensate and block the system. It's a balancing act.
The air flow is adjustable by setting the fan speed and by filter restriction.
Just keep in mind that it is crucial to keep dust and dirt off the coils so good filtration is important.
I'm just the messenger...don't shoot
Air flow determines how much water is removed from the air in your home (assuming a properly sized and efficient AC system). If the air flow is too great, too much moisture is drawn off the coils and back into the air resulting in higher humidity.
Not enough air flow and the coils can freeze condensate and block the system. It's a balancing act.
The air flow is adjustable by setting the fan speed and by filter restriction.
Just keep in mind that it is crucial to keep dust and dirt off the coils so good filtration is important.
I'm just the messenger...don't shoot
I went from a 1 inch thick filter to a 4 inch.
My 'differential' pressure dropped from .30 to .10 (inches of water) on a 'new' 4 inch filter.
I'm using a MERV 13 filter that traps most dust.
I choose the AprilAir filter and enclosure .... Best thing I ever did.
The amount of dust that settles on furniture drastically decreased.
Like oil filter efficiency, you have to understand what the % is in relation to particle size.
This chart shows it.
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when your home was built I would think the air mechanical company did a load calculation test on the home and the return was sized appropriately for the living space being conditioned. my home is slightly larger with 9ft ceilings the living room and master has 11ft tray ceilings and my return is a 20x25x1.
When I had my unit replaced a few years ago with a Lennox, it came with a MERV11 5" filter. I asked them about restriction and was told that most newer systems are designed to work with the higher MERV, more restrictive filters. They also said that if you have an older system which uses a 1" filter or similar, to stick with the less restrictive because those systems weren't designed with high filter ratings because they weren't really a "thing" back in the day. How much of this is true, I don't know. I just replace them with the same filter that came with the unit (Healthy Climate) since they are OEM and about the same price as some of the AM options. I haven't had a problem.
AZjeff
$50 Site Donor 2023
One would think so, until I found out an elderly neighbor's house with less square footage has a 20 x 30 return filter. Same builder, HVAC equipment etc. All of the HVAC ducting and the air handler are in the attic of these homes and there are complaints that the ducts are undersized and rooms farthest from the air handler are hot/cold. We have that problem with 2 bedrooms, the one that faces north is cold in the winter and the one that faces east and gets full morning sun is hot in summer. They may be to size but barely. There was talk of a lawsuit.
@MasterSolenoid what are the dimensions of your filter and how often do you change it? The delta P drop from .3 to .1 WC is significant. Maybe it's time I did the same thing.
I use MERV 12 filters and measure the pressure drop to change my filters out.
Also I hate when HVAC techs say "more restriction is going to put more load on the blower motor. " It's a squirrel cage (forward curve centrifugal fan).
In reality your HVAC system may be designed to run at a specific pressure drop. So less pressure it can overheat and more pressure it may not move enough airflow over the coils.(Freeze up) But you can check this against the acceptable pressure drops in the owners manual.
As flow goes down so does power usage.
3M adds more pleats to their higher merv rated filters to increase the flow area which is how they reduce the pressure drop. Most cheap higher merv filters don't do that so just keep that in mind.
Also I hate when HVAC techs say "more restriction is going to put more load on the blower motor. " It's a squirrel cage (forward curve centrifugal fan).
In reality your HVAC system may be designed to run at a specific pressure drop. So less pressure it can overheat and more pressure it may not move enough airflow over the coils.(Freeze up) But you can check this against the acceptable pressure drops in the owners manual.
As flow goes down so does power usage.
3M adds more pleats to their higher merv rated filters to increase the flow area which is how they reduce the pressure drop. Most cheap higher merv filters don't do that so just keep that in mind.