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Do my AC air intake vents really need air filters?

Is there any downside to removing them? Like are the blowers expecting a certain level of resistance from the filters in order to work properly?

Could I damage the blower or the AC unit by not having a filter installed?

I really want the least amount of resistance in order to cool the house as fast as possible during these hot summer days.

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    All ac coils will need cleaned after a while. This can dramatically improve air flow. Best to let a pro do this. Running without a filter will cause the coil to get nasty much quicker. Also investigate if you can set the fan to a higher speed. Many come set on the low speed. – Kris Aug 19 at 13:29
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    In addition to the other answers, the problem may not be the filter. If you've routinely left your filters to get full of crud, or if it's a bad filter that doesn't seal well, then your fan motor may itself be absolutely full of dust and the blades may just be hotdogs now instead of airfoils. Before we go full MacGyver, take a minute, in addition to getting your AC coil inspected and cleaned, to also pull out the blower fan and see if that needs a good muck-out. From other comments you say it's a reusable metal filter - some of those can leak fine dust like crazy. Check your fan and coil. – J... Aug 19 at 16:16
  • Consider using additional fans to distribute the cold air around the house. This both makes it feel cooler and gives the AC warm air to cool. – Tomáš Zato - Reinstate Monica Aug 21 at 14:26
  • Sort of defeats the whole purpose of having central air. – Outdated Computer Tech Aug 22 at 8:34
  • Eliminating resistance can actually reduce the cooling (or increasing the fan speed beyond the design criteria) the evaporator coil needs the air to be in contact with the coil/fins to remove the heat from the air, there are flow curves for establishing the correct flow below the design will cause icing in most systems above design can damage the duct work. Popping a trunk line in a wall is very expensive. A friend that tapped his blower motor to high speed it split the trunk line in the wall we had to pull the sheetrock and remove the trunk line all the way up to the 2nd floor what a mess – Ed Beal Oct 4 at 16:44
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Yes, you'll distribute crud through your ventilation. On top of that, you'll accumulate crud in your AC unit. BAAAAADDD idea.

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    Which will not only reduce the efficiency of the AC, overcool the coil, and excessively dehumidify, but in winter (if you have such a thing) that clogged AC coil will also restrict the airflow through the furnace and can cause it to start overheating, short cycling, etc. Keeping clean filters installed is the best thing you can do for an HVAC system. Removing them, the worst. – J... Aug 19 at 16:13
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Yep... "BAAAADDD" idea. Don't remove your filters, you'll gum up your equipment. Nobody's house is "lint free".

I really want the least amount of resistance in order to cool the house as fast as possible during these hot summer days. Wondering what you guys think about this, thanks.

How about OTHER sources of "resistance". Simple things like, is your condenser exposed to direct sunlight? Are the coils of both the condenser and the evaporator clean? Is your current air filter new?

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  • It's a metal reusable filter. – Outdated Computer Tech Aug 19 at 3:54
  • Ok then make sure it's clean ;) What I'm getting at is there's more than just airflow through the system. You're moving heat. And anything that interferes with that heat transfer is going to reduce the efficiency of your system. – Kyle B Aug 19 at 3:56
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    If your filters are the washable reusable type, get at least one extra filter and it would be best to get a full set. That way you when you remove the dirty filter for cleaning you can immediately replace it with a clean, dry filter. – Jim Stewart Aug 19 at 16:30
  • Definitely good point on the position of the condenser. If sun shines on it, that's really bad. – Tomáš Zato - Reinstate Monica Aug 21 at 14:25
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The air handler is designed to work with a certain amount of resistance on the air inlet side as well as on the output side. If you would remove all resistance on the inlet side, the air handler motor could overspeed and be damaged.

Modern motor controls may limit the overspeeding risk, but most definitely in the past fan motors were burned up by overspeeding from unloading the inlet. I have been told this by an a/c tech, and 55 years ago I destroyed an expensive fan motor by running it without the loading filter on the inlet side. My landlord was not happy with me, and to this day I can hear her blistering criticism of how I treated her property.

The fact is that the loading of the ductwork on the output side is almost certainly enough loading to prevent burning up the motor even with the filters removed, but this would pressurize the ductwork beyond design limits and would cause higher air flow through the ductwork (and through the a/c coil and furnace heat exchanger) than designed.

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I was naive when I moved into my first apartment with an HVAC. But the owners were also negligent and did not keep up with a maintenance schedule. I was later told that they replace the filter "once a year" but privately that it was more like "only when people ask".

What happened was the unit never had a filter installed or it had a filter and it was never replaced (I don't remember which). Because it has AC, there is a pipe to drain the water that accumulates.

Well, the pipe got clogged up with lint and other debris through regular use. And when the water had nowhere else to go, it started to pool onto the floor of the storage closet. The closet was shut and I never looked at it; until I started hearing an ominous "drip-drip-drip" sound coming from it. The water had soaked the carpet, waterlogged everything beneath, and had started to pool. Mold had also started to grow into the wall.

I've never forgotten to check the filter since.

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  • Classic example of 'penny wise, pound foolish' – Glen Yates Aug 20 at 20:08
  • other than the filter that is placed where the air intake is. Are there other filters i'm not aware of? – Outdated Computer Tech Aug 21 at 2:22
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All of the answers are to the question of whether your HVAC system needs a filter. However, that's not what the wording in the question asks:

Do my AC air intake vents really need air filters?

If you're referring to filters in the return vents, that's a different question. Just in case that's actually what you're asking, let me clarify.

The air handler should have a filter in or next to the furnace that filters all of the air as it goes in. You need that and that's the only filter you should have.

Supplemental filters are sold for the registers and/or return vents. Those are a bad idea. Best case, they're thin and not dense, and don't have much air resistance. They will degrade system performance a little but aren't likely to damage it. They will accumulate some dirt and discolor over time but don't really add any useful filtration, so they're a waste of money and your system won't be as efficient.

If you add anything to the vents that does useful filtration, those will add excessive air resistance. System efficiency will suffer and it can strain the system.

The HVAC system is designed to need only the central filter, and it should do all of the required air filtration. If the central filter is not doing an adequate job, use a filter with a higher MERV rating and/or replace it more often.

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  • Yea, now i'm honestly getting confused. Maybe some visuals might be useful. I'm referring to these: i.imgur.com/sjwp38e.png – Outdated Computer Tech Aug 22 at 8:31
  • Im assume these are called intake vents, because it takes IN warm air. Are you all saying there are 2 separate vents that require filters? Downstairs we have a 20x20 filter, and up we have a 30x14. – Outdated Computer Tech Aug 22 at 8:32
  • @Sickest, the kind of filter in your image is what goes into the air handler (inside or next to the furnace). It sounds like you have two zones (two furnaces, one to handle the upstairs and one for the downstairs). The air handlers and ductwork aren't called vents. Vents are the grills mostly in the living areas (there are often a few in utility areas also to condition the air there). The conditioned air enters the living spaces via grills/vents, typically in floors, ceilings, or walls. (cont'd) – fixer1234 Aug 22 at 10:08
  • To get the air back to the furnace, each zone has one or more return vents, typically a large square grill in a wall. What I was concerned you were referring to, based on the question wording, was the vents in the living areas. Filter material is sold to stick inside those vents, in addition to the normal filter in the air handler. Those supplemental room vent filters are what is not a good idea. – fixer1234 Aug 22 at 10:08
  • For me those "return vents" have filters (2 metal reusable ones) which i've recently replaced with the image above because I honestly could not tell if the reusable ones are good or bad. But I do know they are both 25 years old. I've never seen filters at our blower/furnace. Our filters have always been placed inside the house, 1 upstairs, 1 downstairs. 1 of our blowers is in the garage, and 1 is in the attic. – Outdated Computer Tech Aug 22 at 17:23

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