Recommendations for Home A/C Filters

[tez929rr]

Between the house and outbuildings we have 4 heat pumps and a mini split system. I usually stop by Home Depot or WalMart and grab what looks decent. But the array of filters is daunting - I figure the highest priced ones are not worth the dollars but I don’t really know. Any recommendations from someone truly informed? I’m buying replacement filters tomorrow.

 

[PoorUB]

Just buy the low priced pleated paper filters. MERV 8 is fine, if you can find them, 10 or 11 is fine too. Anything fancy and claiming high efficiency is a waste of money and often the filters that make claims of high efficiency air cleaning are more restrictive and can screw up your system with reduced air flow.

 

[danski0224]

Plain fiberglass.

Almost all residential systems cannot handle anything more.

 

[PoorUB]

Plain fiberglass.

Almost all residential systems cannot handle anything more.

No way would I use fiberglass with AC or a heat pump. Fiberglass barely filters at all an your A coil will be the next "filter" in line and get plugged up with dust.

 

[mervyn]

I use the cheap ones and Change em every 2 or 3 months

 

[danski0224]

No way would I use fiberglass with AC or a heat pump. Fiberglass barely filters at all an your A coil will be the next "filter" in line and get plugged up with dust.

The systems do not have the available fan (static pressure) headroom to use anything more restrictive than a plain fiberglass filter.

It costs more money to use a pleated filter. Less airflow = less delivered btu's.

If the filter rack and stuff after the fiberglass filter is sealed properly, the filter does the job.

Plenty of ****** filter installs that allow dirt to be sucked in AFTER the filter.

 

[Dakotadadv8]

3M Filtrete 2200 is not bad costs more but does a great job.

 

[PoorUB]

The systems do not have the available fan (static pressure) headroom to use anything more restrictive than a plain fiberglass filter.

It costs more money to use a pleated filter. Less airflow = less delivered btu's.

If the filter rack and stuff after the fiberglass filter is sealed properly, the filter does the job.

Plenty of ****** filter installs that allow dirt to be sucked in AFTER the filter.

I will argue that to my death. It may have been true with the old belt drive oil burners, but newer systems can easily handle pleated paper filter.

Plus the fiberglass filter will pass all kinds of dust and **** and plug up the A-coil. I have seen it happen every time. How much have you gained with a plugged up A-coil?

If a pleated paper filter cuases too much restiction, the system was designed poorly. I have serviced 5 ton AC units on reidential air handlers with 20x20 pleated paper filters and they ran fine. I would recommend a larger filter, but as long as they were changed regularly it will work.

 

[danski0224]

If you check the TESP, you will find that it doesn't work.

 

[mrbill55]

For me, I'm a little different, I replaced my disposable filters with stainless steel, washable ones. I keep one regular paper filter to use for 24 hours while I wash the stainless units, then reinstall and forget about them for a while.

Return on investment, that depends on how many times you change your filter each year.

Bill S.

 

[P0234]

I like the Filtrete allergy defense. About 10% more expensive than the cheap Honeywell filters but have almost twice the pleats (17 vs 9).

 

[DrinkMan]

For me, I'm a little different, I replaced my disposable filters with stainless steel, washable ones. I keep one regular paper filter to use for 24 hours while I wash the stainless units, then reinstall and forget about them for a while.

Return on investment, that depends on how many times you change your filter each year.

Bill S.

I do similar. Only difference is that as part of the semi-annual checkup by the HVAC company, they clean them for me (after all, they are charging a pretty healthy annual amount to maintain the systems...I'm ready for all the responses that these contracts are a rip-off).

 

[toyotadriver]

I buy filters from this company in bulk. I use the MERV 11 filters. I have plenty of air intake space (much more than I need) so I like the higher MERV filters. Takes 4 filters every time I change them.

https://www.discountfilters.com/furnace-air-filters/

 

[PoorUB]

If you check the TESP, you will find that it doesn't work.

I have checked more times than I can count.

Either way a fiberglass filter is barely better than no filter at all. All it stops is tha big chunks. A lot of dust still gets through and plugs up the A-coil.

 

[FredWanaker]

State of California did an energy and efficiency study to see what worked best. 3M Filtrete 1900 series (Lowes or ACE) has the lowest restriction and best filtration. The only filters that have lower filtration are the MERV 3 keep you cat out of the HVAC duct fiberglass filters. The medium MERV filters have more restriction than the 1900. Since California got involved, there is now a small box on each filter filled in with the resistance information. It will state inches of mercury resistance at a given CFM. Many HVAC systems cannot handle anything more resistive than a MERV 3 without long term damage unless the filter box or inlet is enlarged to handle larger filters. For example, I run a 2.5 ton HVAC in a 1400 sq ft house. The CFM is right at 1000 CFM (350 - 400 CFM per ton) With a (25 x 30) main inlet, and a (24 x 14) ceiling inlet at the back of the house that gives me 750 sq inches plus 336 = 1086 sq inches which barely gets me under the manufacturer published specs using the Flitrete 1900. These systems were designed mostly for a MERV 3 filter, but they don't do nearly as good a job as the higher filtration units. My ducts are still spotless. They would be full of debris after 20 years if I used the MERV 3. A 2" or 4" thick filter has almost as much resistance as a 1". Figure that.

 

[Houdini5150]

I use whatever is one step above the fiber glass filters and change them every 3 months

 

[Mike007]

I have checked more times than I can count.

Either way a fiberglass filter is barely better than no filter at all. All it stops is tha big chunks. A lot of dust still gets through and plugs up the A-coil.

Unfortunately that's what many equipment manufacturers recommend. Cheap spun fiberglass filters. Most residential systems are short on airflow to begin with. Usually due to improper ductwork and/or oversized equipment. Around my area, at least. Then you throw a pleated filter in the system and the furnace runs hot and cycles on high limit and the AC freezes or runs just above the freezing point. Then it gets a little dirt on the filter and it freezes.

 

[FredWanaker]

If you look at most certified air filters, they will have this label on printed on them. It will list the MERV, what percentage of particles it catches, and also what the resistance is to airflow at different CFM's. In my research I found that the Filtrete 1900 (this label 20"x25") had not only a high MERV but also the lowest resistance to airflow. Many MERV 5 - 13 filters have significantly more resistance to airflow than this model does. The ONLY filters I found that had less were fiberglass MERV 1 thru MERV 3 designed to stop the kids, dog and cat from entering air duct. They will catch hair and large fibers but not the small dust particles that will eventually build up on the AC evaporator coils. The resistance may seem trivial but it is not. As the prior post said, when ducting resistance and the units own resistance is added in, most units cannot handle the increased resistance of the pleated air filters. That is a fact and not a speculation. I spent considerable time learning the way to measure resistance, then buying the equipment, then measuring mine. It barely meets the manufacturer's (Carrier) combined air flow resistance specs when the AC is on - and it took some work to get there. Most HVAC service guys have not a clue about this and frankly if you use the wrong filter and cut the life of your system in half, it just means more business for the HVAC folks.

 

[danski0224]

It barely meets the manufacturer's (Carrier) combined air flow resistance specs when the AC is on

What size is equipment?

 

[FredWanaker]

What size is equipment?

the model I have is 2.5 ton on the AC with a 3 ton air handler, however the manual covers the static pressures on the entire series which goes up to significantly larger Carrier units.

example

 

[bonneyman]

As a licensed contractor for 14 years I recommended folks use a pleated filter. MERV 8 was my standard filter, but I offered MERV 11 for special needs customers (allergies, fine dust areas, specialized applications). Problem jobs (excessive noise or airflow restrictions) I'd call in an air balance specialist and do what they recommended. Only had a few of those.

The local Flanders dealer offered me a great deal on special sizes, and they took standard size filters and cut them down professionally to what I needed at a $1 a cut. I told my customers with the types of conditions in our area to change filters once a month. And to do it when the electric bill came in - cause the utility is never gonna fail to tell you it's payment time!
And I told customers if they bought filters a dozen at a time, I'd deliver them for free. Then they'd be set for a year of monthly changes, I could collect when I was there taking the order, and fit them into my route later when they were ready to be dropped off. Worked great.

I used this kind of filter

PerfectPleat® ULTRA

<p style="text-align: left">The PerfectPleat ULTRA is a high-capacity self-supported pleated filter with an added antimicrobial to preserve media integrity, especially in high-moisture environments. The low-pressure drop and high dust-holding capacity can help reduce energy use and overall...

www.aafintl.com

These had the added benefit of an anti-microbial coating. So any entrapped mold or allergen spores captured with the dirt wouldn't proliferate during the month.

 

[Bert_]

Just looked at an a/c yesterday that wasn't cooling well. Sure enough it had a 1" pleated filter and the coil was running about 35*. Told her to run the cheap fiberglass filters.

 

[danski0224]

the model I have is 2.5 ton on the AC with a 3 ton air handler, however the manual covers the static pressures on the entire series which goes up to significantly larger Carrier units.

example

That's likely why yours works, a small system and (assumed) large filter sizes in Post #15.

In my experience, your system is an anomaly.

It is far more likely for me to see someone trying to pull 4 tons of cooling through a 16 x 25 filter on the side of the furnace, and this doesn't work.

I also disagree with the possibility of leaving the air filter out of the measuring process in that video. If you are using an air filter, then measure the system with it in place.

 

[FredWanaker]

As a licensed contractor for 14 years I recommended folks use a pleated filter. MERV 8 was my standard filter, but I offered MERV 11 for special needs customers (allergies, fine dust areas, specialized applications). Problem jobs (excessive noise or airflow restrictions) I'd call in an air balance specialist and do what they recommended. Only had a few of those.

The local Flanders dealer offered me a great deal on special sizes, and they took standard size filters and cut them down professionally to what I needed at a $1 a cut. I told my customers with the types of conditions in our area to change filters once a month. And to do it when the electric bill came in - cause the utility is never gonna fail to tell you it's payment time!
And I told customers if they bought filters a dozen at a time, I'd deliver them for free. Then they'd be set for a year of monthly changes, I could collect when I was there taking the order, and fit them into my route later when they were ready to be dropped off. Worked great.

I used this kind of filter

PerfectPleat® ULTRA

<p style="text-align: left">The PerfectPleat ULTRA is a high-capacity self-supported pleated filter with an added antimicrobial to preserve media integrity, especially in high-moisture environments. The low-pressure drop and high dust-holding capacity can help reduce energy use and overall...

www.aafintl.com

These had the added benefit of an anti-microbial coating. So any entrapped mold or allergen spores captured with the dirt wouldn't proliferate during the month.

Using your link, the Flanders (and I looked at them a couple years ago) shows an initial resistance of .42 inches at 500 fpm on a 20X25X1 at 1750 CFM compared to .39 inches on the Filtrete 1900 at the same CFM. They recommend changing at 1" or over double that. Many air handlers are rated to come in way under 1 inch total. Dropping down, at 300 fpm (1050 cfm) the Flanders is abou .22inches initial resistance whereas the Filtrete 1900 is .18 inches. The MERV on the 3M Filtrete 1900 is 13 while the MERV on the Flanders is only MERV 8. Filtrete is a better filter both on MERV and lower initial resistance. The labs also included Flanders filters in their testing. Lawrence Livermore Labs was involved in the testing. They wanted to determine energy efficiency of various filters commonly used in residential HVAC systems.

The study is here https://efiling.energy.ca.gov/GetDocument.aspx?tn=223245-14&DocumentContentId=27687

 

[PoorUB]

Using your link, the Flanders (and I looked at them a couple years ago) shows an initial resistance of .42 inches at 500 fpm on a 20X25X1 at 1750 CFM compared to .39 inches on the Filtrete 1900 at the same CFM. They recommend changing at 1" or over double that. Many air handlers are rated to come in way under 1 inch total. Dropping down, at 300 fpm (1050 cfm) the Flanders is abou .22inches initial resistance whereas the Filtrete 1900 is .18 inches. The MERV on the 3M Filtrete 1900 is 13 while the MERV on the Flanders is only MERV 8. Filtrete is a better filter both on MERV and lower initial resistance. The labs also included Flanders filters in their testing. Lawrence Livermore Labs was involved in the testing. They wanted to determine energy efficiency of various filters commonly used in residential HVAC systems.

The study is here https://efiling.energy.ca.gov/GetDocument.aspx?tn=223245-14&DocumentContentId=27687

For 1750 CFM one 20x25x1 filter is not enough, no matter the type of filter you use. A low resistance filter may work, but in reality you need two of them.
I have made it work, but wouldn't recommend it.
At that CFM we would do two returns, a side and bottom, or both sides and run two filters

 

[FredWanaker]

For 1750 CFM one 20x25x1 filter is not enough, no matter the type of filter you use. A low resistance filter may work, but in reality you need two of them.
I have made it work, but wouldn't recommend it.
At that CFM we would do two returns, a side and bottom, or both sides and run two filters

yes to what you said. We have a 20x25x1 at the return duct and a 24x14x1 in the ceiling at the back of the hours for the 3-ton air handler. That is barely enough with the 3M Filtrete 1900. I could not find another pleated filter that would work, and there is no room for more filter area. The next step are the low MERV fiberglass filters but that would mean introducing dirt into the system and evap coil. It is a dance. Most people walk into a big box store, chose a pretty filter and begin to destroy their HVAC system without knowing it. Hence the original poster wanted to know what was a good filter. I think they left the room a long time ago when the answer became too technical for "tell me what to buy." But, that is how it is. Residential systems were not designed for much more than a horse hair or fiberglass filter. It took me considerable tuning to be able to use a high MERV filter and meet the manufacturer's specs.

 

[danski0224]

For 1750 CFM one 20x25x1 filter is not enough, no matter the type of filter you use. A low resistance filter may work, but in reality you need two of them.
I have made it work, but wouldn't recommend it.
At that CFM we would do two returns, a side and bottom, or both sides and run two filters

Two returns is actually in the GD installation manual for furnaces at 1600 CFM and up... at least it was.

Not that anyone outside of maybe 7 people would actually read that...

 

[bonneyman]

Two returns is actually in the GD installation manual for furnaces at 1600 CFM and up... at least it was.

Not that anyone outside of maybe 7 people would actually read that...

10-4 Most new HVAC units require airflow that the typical duct systems can't reliably provide. Putting in 2 filters (thus having say 40x25x1 instead of 20x25x1) would help let the system "breathe" easier. Won't eliminate bad duct design but would help airflow requirements.
Walked into many a new home with A/C issues to find single filters and - when the filter is pulled out - revealed squashed flex ducts above the filter box that were filthy. Flex duct already has more internal friction than sheet metal ducts, and are barely passable when installed properly. Most are not, and thus are restrictive to airflow. Add to this a too small filter, and the system is going to be having problems down the road. Unfortunately, by the time new home owners find out about it, the installing contractors warranty has expired, and they get the "sorry, nothing we can do now" or "nobody else in the sub-division is complaining" routine. And they don't want to pay me redoing/straightening the duct system and performing air balance testing (understandable).
Luckily my SIL's house has two filters, and she's religious about replacing the filters.

 

[DC73]

I use a MERV 11 or 12 in my systems depending on which is more readily available. I get good house dust control with this level of filtration and my old system handles them very well. However, I tried MERV 13 once and didn't like the sounds my unit made. It seems this level of filtration is a litte too restrictive for my system and that's something to consider. For best filtration, use the highest MERV rated filter you can but know that you can go too far. I would venture to say that most systems can use a MERV 11 or 12 but beyond that, the system should be specifically designed for the higher MERV rated filters.

I also discovered on my house system that it was set up for a 1" filter but had a bracket that could be removed so the housing could accommodate 2" filters. I switched to a 2" filter immediately and got much better filtration as a result. With a 2" filter and MERV 12, I can now easily go 3 months between filter changes and could probably go longer given how they look when I pull them out.

DC

 

[Jim greengo]

True blue merv3 from menards.
Change them once a month,no big deal.

 

[FredWanaker]

I was in the blue box store yesterday. Their $5-$6 3m MERV5 is the basic basic filter they sell. Comparing the static pressure at various air flows to the 3M MERV 13 1900 Filter, the 1900 has lower resistance to air flow. It costs 4x as much but it is the ONLY filter that is closer to the MERV 3 blue catch your cat fiberglass filters. I know that my system works Ok with them because I have tested the static pressure and it is within the manufacturer specs. Even that MERV 5 basic filter they sell would not be. Go buy the equipment and test your own system and you will see what I am speaking of. Most HVAC repair people haven't a clue how to do a static test. A few do. And yes, a 40x25x1 would be much better but there is no room for that where the inlet is. The house does not warrant spending $5K to redesign the inlet system, especially when the woke folks are trying to ban anything but electric baseboard heating or heat pumps in this state (which freeze up here because it is common to be 33F and foggy here. Heat pump coils simply ice up.)

 

[bonneyman]

Depending on the system I've cut out another hole in the drywall and "added" another filter. On rooftop units I've modified the ductwork so I could install a 4" thick filter. Or if I had room I'd make a sheet metal A=frame and put two filters in at an angle and drop the assembly into the exisiting filter holder. Whatever I could do to help airflow.
Mainly I've done this to address noise problems but then later in my career discovered it helped filter resistance. "Happy accidents" maybe?

 

[JackOfDiamonds]

So much bad information in this thread.

First of all, there is ZERO correlation between the particle removal rating of any given filter and its restriction. The only way you can know the restriction is by measuring or by trusting the published data. The reason is that while more-restrictive fabrics remove typically remove more particles, manufacturers have the option of simply adding more pleats to reduce restriction. So a fabric that is twice as restrictive will have exactly the same restriction if the manufacturer simply uses twice the pleats.

This is why the idea that the cheap fiberglass filters are "less restrictive" is total garbage. The cheap filters don't use any pleats at all! So they probably filter like garbage and are still restrictive...there's no way to know.

Good filters have the restriction printed right on the filter. I buy Honeywell filters that literally print the restriction vs. airflow right on the filter. Go ahead and compare filters with different MERV ratings...there's no difference in restriction, because the manufacturers compensate.

Second, if you really want to know the restriction of a filter, either when new or when dirty, just measure it. You don't need an electronic meter. Just a piece of clear hose. Make a loop in a piece of 1/2" clear hose and put some water in it, to form a P-trap. Tap one end of the hose into the plenum downstream of your filter. Leave the other end open. The difference between the water levels will be your filter restriction...1/4" difference in level means 1/4" W.C. restriction. I have a tap in all my furnaces for doing this. Just drill a hole with a step bit, and pop in a cork when done measuring.

I was skeptical that 4" thick filters were really good for 1 year. After I switched my system to a 4-inch filter, I was still measuring less restriction wit the 4-inch filter after 1 year, than with a BRAND NEW 1 inch filter. So I'm a big fan of the thick filters.

 

[FredWanaker]

most manufacturers don't post their specs online. California requires it on the package in a standardized form. One can compare any two filters that way if the manufacturer prints the filters for sale in California. BTW when I say fiberglass, I literally mean spun glass that you can almost see thru. They catch hair and some dust but aren't something that will do a good job at cleaning up the air. Just make sure that when going to pleated filters you take the time to know what the air resistance will do to your system. As others have stated, do not assume that a medium priced filter will do a good job of passing air thru it. It may do a worse job than a filter with more pleats. The Filtrete 1900 has a lot of pleats in it, and that is why the resistance is less than a lower merv filter that looks like it would breathe easier. In general 4" filters do pass more air thru them based on the California / Lawrence Livermore study, but barely. It is a long read and I have posted a link to the pdf on it before. However not all 4" filters will offer lower resistance than 1" filters. If the air handler motor has to work harder to pull more air it will not only shorten its life, but it will raise your electric bill. If you have a system where the gas furnace uses the same air handler, which is common, if the air flow is reduced too much the heat manifolds can get too hot and crack. It really pays to study these things before just grabbing any filter off the shelf. There are a couple people here who understand this but a good number of people do not, and as a result they fall victim to marketing on many filter lines.

 

[danski0224]

This is why the idea that the cheap fiberglass filters are "less restrictive" is total garbage. The cheap filters don't use any pleats at all! So they probably filter like garbage and are still restrictive...there's no way to know.

This is pretty much ********.

The fiberglass filters ARE less restrictive.

Yes, if the number of pleats goes up, the square footage/inches of filter media area goes up and therefore given the same filter size (say, 16 x 25) and same airflow, resistance goes down.

The filter is PART of the system.

The fan in a residential HVAC system can typically handle 0.5" wc of total external static pressure (TESP) and deliver the rated airflow at the least amount of electricity used.

Your 0.25" wc example measurement of filter restriction can be 50% of the available total TESP of the fan.

Not good.

 

[JackOfDiamonds]

Thanks for providing the info about 1/2" WC limit. I never knew if there was a limit or guideline for how much pressure drop is acceptable. I was only comparing my new filter to the old one.

If the 1/2" figure is actually the right number to go by, I could run my current filters until I hot that limit. Right now I just change yearly.

Actually my numbers when I compared filters were more like this:

No filter: 0"
New 4" filter (Honeywell MERV8): 1/16-1/8"
1-year old 4" filter: 3/8 - 7/16"
New 1" filter (filtrete midrange): 1/2"
3-month old 1" filter 5/8-3/4"

 

[danski0224]

That limit also includes pressure drop from AC coil and ductwork.

Air handlers include the evap.

It isn't 0.5" for the filter by itself.

 

[FredWanaker]

The spec will be on a tag on the air handler. For my Carrier it states .5" WC and then in the installation manual it states that includes .10 for the internal fiberglass/horsehair type filter, which if removed can be added back to the total. So for my Carrier it is .50 + .10 since there is no internal filter. The pressure below the air handler includes the inlet air filter(s) The pressure above the air handler includes the evap and ducting resistance. Combined they cannot exceed .60" WC on my unit. If you want your HVAC system to work properly then one has to be sure the manufacturer's specs are adhered to. Almost all units are designed for either the factory 4" accessory filter that goes inline, or the factory 1" FIBERGLASS/Horsehair MERV 1 see thru filter. That is NOT the MERV 4 Basic filter at many hardware stores. It is now a hard to find almost see thru spun fiberglass wool filter. Last place I saw some was ACE had some Flanders MERV 1 sizes. They will stop the cat and its hair from being sucked in but beyond that not much else. I found only two filters that would keep my unit under the manufacturer's spec - the 3M Filterete 1900 and the basic spun fiberglass. Nothing else in the 3M, Flanders, Honeywell etc would work for me. I have two filters, one 25x20x1 and one 24x14x1. The smaller one pulls air from the back of the house but it shares the same inlet as the larger one. There was no room to add an additional inlet due to gas pipes and a water heater. Lots of these split systems are designed to use a spun fiberglass / horsehair type filter internally. When I bought this house the original owner tossed a fiberglass filter into the inlet but never took the horsehair out on the old system from 1980. It was caked with inches of dust while the inlet filter was new. Dumb. If you have an external filter, take the time to look inside your air handler to be sure that the original filter hasn't been forgotten, sitting in there for 10 years collecting dust. FWIW when I traveled for a living, even when visiting a Hilton I would take my flashlight and shine it up at the heater / AC filter in the room. If it was caked with dirt, which they always were, I made engineering come up and replace it. If they didn't, I pulled it out in the morning, left it on the floor and asked for my money back because of the inconvenience and unsanitary conditions.

 

[roc_on_the_rocks]

So much bad information in this thread.

Second, if you really want to know the restriction of a filter, either when new or when dirty, just measure it. You don't need an electronic meter. Just a piece of clear hose. Make a loop in a piece of 1/2" clear hose and put some water in it, to form a P-trap. Tap one end of the hose into the plenum downstream of your filter. Leave the other end open. The difference between the water levels will be your filter restriction...1/4" difference in level means 1/4" W.C. restriction. I have a tap in all my furnaces for doing this. Just drill a hole with a step bit, and pop in a cork when done measuring.

Shouldn't the other end of the hose be connected to the upstream section of the plenum?

 

[JackOfDiamonds]

Shouldn't the other end of the hose be connected to the upstream section of the plenum?

It depends what you want to measure. You can always measure it as well but the upstream pressure is usually practically the same as atmosphere. In my case I want to get a measurement of how much the pressure changes over the life of the filter so it's not important to me if I have some zero crossing error anyway.