# Do anti-allergy air filters hurt air conditioners?
**URL:** https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186
**Category:** Factual Questions
**Created:** [September 4, 2011, 8:59pm UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186 "2011-09-04T20:59:01Z")
**Posts on this page:** 13
**Page:** 1
### Author:  [@No\_Wikipedia\_Cites](https://boards.straightdope.com/u/No_Wikipedia_Cites)
#### Post date: [September 4, 2011, 8:59pm UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186/1 "2011-09-04T20:59:01Z")
I have a unit in an apartment, central air & heating, and the repair guy came over and said I should use a cheap filter (the old timey ones with minimal protection) because the dense anti-allergy filters were too demanding of the system.
However this guy also gave me false information saying that there would be no way to replace the system where it is (in the ceiling) and i would need to put a replacement in the corner and wall it in. (I posted another question about that). I got a second opinion and the other company said there were units that would fit and to call them back when the unit breaks, years from now.
The home inspector said the unit was 7 years old and 16000BTU heating and 18000 cooling (or 1.5 ton?). The inspector also wrote “12-13 degrees of cooling measured; likely related to poor duct design. 15-20 degrees is considered normal”
So should I throw my 3m anti allergy filter out and put in the cheapos?
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### Author:  [@JKilez](https://boards.straightdope.com/u/JKilez)
#### Post date: [September 5, 2011, 12:02am UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186/2 "2011-09-05T00:02:32Z")
Higher efficiency air filters _will_ reduce air flow to some extent, which may be the repair guy’s point. The efficiency rating is the ability to remove particles, not the mechanical efficiency of the system. If your blower was undersized to begin with, this could make a noticeable difference.
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### Author:  [@Batfish](https://boards.straightdope.com/u/Batfish)
#### Post date: [September 5, 2011, 12:08am UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186/3 "2011-09-05T00:08:16Z")
> [@No\_Wikipedia\_Cites](#):
>
> The home inspector said the unit was 7 years old and 16000BTU heating and 18000 cooling (or 1.5 ton?). The inspector also wrote “12-13 degrees of cooling measured; likely related to poor duct design. 15-20 degrees is considered normal”
If the airflow was restricted by the higher efficiency air filter then the deltaT would be higher, not lower.
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### Author:  [@No\_Wikipedia\_Cites](https://boards.straightdope.com/u/No_Wikipedia_Cites)
#### Post date: [September 5, 2011, 12:13am UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186/4 "2011-09-05T00:13:48Z")
> [@Batfish](#):
>
> If the airflow was restricted by the higher efficiency air filter then the deltaT would be higher, not lower.
So the higher efficiency air filter helps the system by allowing it to cool smaller amounts of air?
I’m not sure which to use, my goal is to prolong the life of the system
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### Author:  [@No\_Wikipedia\_Cites](https://boards.straightdope.com/u/No_Wikipedia_Cites)
#### Post date: [September 5, 2011, 12:16am UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186/5 "2011-09-05T00:16:25Z")
Or maybe the repair guy was afraid the filters would slow air flow down too much so that the air pump would overheat?
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### Author:  [@Snnipe\_70E](https://boards.straightdope.com/u/Snnipe_70E)
#### Post date: [September 5, 2011, 6:40am UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186/6 "2011-09-05T06:40:09Z")
Slowing the air flow to much can cause the cooling coil to ice over.
A good test get a new cheapo filter. start the fan and see how much air comes out of the vents. Then change the filter and compare. If the difference is small then it will probably not matter.
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### Author:  [@raindog](https://boards.straightdope.com/u/raindog)
#### Post date: [September 5, 2011, 1:21pm UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186/7 "2011-09-05T13:21:43Z")
The very dense nylon/polyester (or whatever they’re made of) washable filters are generally bad for your system—particularly for your A/C system.
The other extreme----which is what your guy recommended------_may_ be just as bad.
**All** A/C systems require a certain amount of air to function properly. The system’s blower is designed to deliver the correct amount of air. The designers know that there are “restrictions” to the air flow, and design a blower to “overcome” those restrictions. Examples of restrictions: your duct-work, your A/C coil----and your filter.
The problem with those high-falutin filters is that while they do a good job of filtering air, they provide way, way too much restriction. (which can be measured)
The cheapo filters, however, allow dust to pass through your filter and hit your A/C coil----which in the summer time will be **wet.** Immediately it will be mud, _and over a period of time_ will build up. In HVAC parlance, you have a “dirty (or plugged up) evaporator coil.”
A dirty evaporator coil has the same effect that a super-duper vinyl filter has: severely reduced air flow. And…severely reduced air flow can/will destroy your compressor outside. (read: _expensive_)
My internet advice: Use a good pleated filter and change it regularly. (and how often you should change it is another question altogether) 3M’s [Filtrete](http://www.filtrete.com/wps/portal/3M/en_US/FiltreteUS/Filtrete/Products/Catalog-Air/?PC_7_RJH9U52308MGD0ICA24GES1011_nid=5ZF0147CLCbeQHZF8K475Hgl) is just one example, and you can find pleated filters at any home improvement store.
raindog
HVAC guy
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### Author:  [@raindog](https://boards.straightdope.com/u/raindog)
#### Post date: [September 5, 2011, 1:27pm UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186/8 "2011-09-05T13:27:56Z")
> [@No\_Wikipedia\_Cites](#):
>
> I have a unit in an apartment, central air & heating, and the repair guy came over and said I should use a cheap filter (the old timey ones with minimal protection) because the dense anti-allergy filters were too demanding of the system.
>
> However this guy also gave me false information saying that there would be no way to replace the system where it is (in the ceiling) and i would need to put a replacement in the corner and wall it in. (I posted another question about that). I got a second opinion and the other company said there were units that would fit and to call them back when the unit breaks, years from now.
>
> The home inspector said the unit was 7 years old and 16000BTU heating and 18000 cooling (or 1.5 ton?). The inspector also wrote “12-13 degrees of cooling measured; likely related to poor duct design. 15-20 degrees is considered normal”
>
> So should I throw my 3m anti allergy filter out and put in the cheapos?
ETA: It is unlikely that the home inspector would know the elements of duct design unless he/she had a background in HVAC. He’s correct that a 12-13° split is not good, but I would guess that it is not related to duct design, but something in the refrigeration cycle.
Home inspectors are good, from 30,000 feet. If you’re really interested in the property get a professional to inspect the HVAC system.
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### Author:  [@No\_Wikipedia\_Cites](https://boards.straightdope.com/u/No_Wikipedia_Cites)
#### Post date: [September 5, 2011, 3:14pm UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186/9 "2011-09-05T15:14:47Z")
> [@raindog](#):
>
> Air/?PC\_7\_RJH9U52308MGD0ICA24GES1011\_nid=5ZF0147CLCbeQHZF8K475Hgl"]Filtrete is just one example, and you can find pleated filters at any home improvement store.
Oh I see, that is very helpful of a post and I will be returning my cheapos. HOwever, what level of filtration should I get in the 3m Filtrete ones? It varies from MERV 6 (the lowest they have, ‘dust’ only) to much higher
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### Author:  [@raindog](https://boards.straightdope.com/u/raindog)
#### Post date: [September 5, 2011, 3:37pm UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186/10 "2011-09-05T15:37:17Z")
Even the best Filtrete (which presumably has the highest restriction, right?) will not have anywhere near the level of restriction that those permanent filters do, and they will not have too much restriction.
Any of them will work fine. (and, really, any good pleated filter will do a good job)
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### Author:  [@ZenBeam](https://boards.straightdope.com/u/ZenBeam)
#### Post date: [September 5, 2011, 4:03pm UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186/11 "2011-09-05T16:03:22Z")
Don’t filters have the amount of airflow restriction labeled on them? (We have an electronic air filter, so I never have to buy filters.)
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### Author:  [@raindog](https://boards.straightdope.com/u/raindog)
#### Post date: [September 5, 2011, 4:09pm UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186/12 "2011-09-05T16:09:57Z")
> [@ZenBeam](#):
>
> Don’t filters have the amount of airflow restriction labeled on them? (We have an electronic air filter, so I never have to buy filters.)
No, in part because there are other variables-----outside of the filter itself------that will influence actual pressure drop.
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### Author:  [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)
#### Post date: [September 5, 2011, 5:03pm UTC](https://boards.straightdope.com/t/do-anti-allergy-air-filters-hurt-air-conditioners/595186/13 "2011-09-05T17:03:44Z")
I normally get the red “1000” Filtretes. They seem to strike a good balance of catching crud in the air and not being overly restrictive, and not being excessively expensive.
Definitely avoid the cheapies sold at the grocery store - those things with such an open mesh that you could read through them don’t catch much more than insects and airborne pebbles. As **raindog** said, the next line of filtration is unintentional - the dust will stick to the wet evaporator coil. The cheap pleated filters are at the other end of the spectrum - they’re so restrictive even when new that the airflow through them will suck them into a dish shape.
Above all, the best advice I have regarding filters is to change them regularly. I’ve been changing ours monthly, which might be a bit excessive, but compared to repairs or the inconvenience of having the AC fail when it’s 95 degrees, it’s worth it. For their part, 3M says the filters last “up to” 3 months.