Do AC Return Vents Need Filters to Reduce Dust?


Some people wish to filter out more dust and they are thinking of putting filters on their AC return vents. However, adding more filters may harm your AC. So, do you really need to put filters on the return vents?

AC return vents do not need filters. Putting extra filters on air conditioning return vents will reduce the performance and lifespan of the air conditioner. The filters will reduce the airflow and put stress on the AC fan motor. The air conditioner already has a filter right before its cooling coil and thus, additional return vent filters are unnecessary.

Adding filters on the return vent do more harm than good. However, there are times where doing so makes total sense.

Why You Don’t Need Return Vent Filters?

Every air conditioner has a built-in filter to prevent dust from entering into its cooling coil. The AC filter is not meant to provide clean air for your house but protect the AC itself.

Air conditioners are designed to operate within a range of airflow. At the same time, filters are meant to block dust but they also reduce airflow. So, when you put filters on the return vents, you’ll start to stress and suffocate your AC.

When an air conditioner does not have sufficient airflow, the following problems may occur:

  • High fan motor running current and eventually burn.
  • Insufficient cooling and thus, constantly running at full capacity and consume more power.
  • Coil freezing and the AC stops functioning.
  • Water dripping due to condensation happens at the supply air outlet.

Therefore, unless it is really necessary, it is not a good idea to put filters on return vents. So, what do I mean by “really necessary”?

When You Should Put Filters on Return Vents?

You should put filters on return vents when you are unable to wash/install the filter in the AC itself due to space limitation or accessibility issues.

Bad AC installation does not give enough space for people to remove and clean the filter. When we encounter such a problem, we’ll advise the customer to forget about the original AC filter and put new filters on every return vents.

If you have the same problem, remember that you should put filters on EVERY return vent to prevent dust from entering into the AC coil. However, it’s not the end of the world if you can’t reach a vent or two. Your AC is still fine to operate. It’s just that your AC coil will get dirty sooner and a coil cleaning service is quite expensive.

Alternative to Return Vent Filters

If your air conditioner was done badly and you don’t have space to install back its filter. I have some suggestions for you.

Normally, an AC filter is one big rectangular piece. However, you can buy a foldable filter where the one big piece filter is split into 3-4 pieces and linked with hinges. With that, the filter suddenly doesn’t require that much space to put back into the AC.

If you can’t find the hinged foldable filter, you can use smaller pieces of filter. Then, you can put a string or something on them so that you can pull them out when it’s time to service.

By the way, while I was doing my research, I found some great air filters on Amazon:

Another way to avoid using return vent filters is to put a filter in the return air duct right before it enters the air conditioner. The principle is the same as the original AC filter but, you forget about the original filter location and put it in the return duct instead.

Putting a filter in the return duct requires you to cut an opening, put two rails (top and bottom) to slot in and hold the filter. Ensure the filter stays firmly because the return air has a great amount of suction.

Problems with Return Vent Filters

If you have to put filters on return vents, here are a few problems that you can expect:

1. You May Need to Buy New Return Vents

Most return vents don’t have a hinge for people to open because you don’t need to. Besides, they don’t have a slot to hold the filter. So, if your return vents are high up the ceiling, you’ll need to get some new vents.

If your return vents are on the floor, you may not need new vents. You can put the filter on the vents but it’ll not be good-looking and it may move around when the AC is not operating (filters are very light). Besides, some people also said that their return vent filters bend into the vent due to strong suction.

So, I went on to search for a good return vent that have a dedicated filter slot on Amazon, here is my top pick:

2. You’ll Need to Spend More on Filters

A good central air conditioning system has a return vent in every room to accurately control the temperature of each room as well as maintaining equal air pressure in every room. Thus, a central air conditioner can have 4-5 return vents in a house. So, you’ll need to clean all of them.

In addition, there is a limit on how many times a filter can be washed. Many manufacturers recommend changing a new filter after 3-4 times of washing. So, you’ll need to replace all of them after a while.

3. You’ll Need to Seal the Original Filter Opening

After you removed the AC filter, there is a hole in the air conditioner and you’ll need to seal it. Otherwise, air will go in from the opening together with all the dust.

Furthermore, your AC will be getting the return air from the opening but not from the return vent. Hence, temperature control can go haywire.

4. If You Have a Fresh Air Intake, You’ll Need a Filter for That Too

Some central air conditioners have ducted in fresh air from outside into its return air plenum. Then, the AC filter will block dust from both the fresh air and return air.

If your AC has a fresh air intake, you’ll need to put a filter either in the duct or the external vent just like the return vents. There you go, one more filter to wash/replace, and one more vent to change.

Worry If the Return Air Duct is Dusty?

Some people want to put filters on return vents to prevent dust from building up inside their return air duct. If you too want to do so, be sure to remove the original AC filter and seal the opening so that your AC won’t suffer from low airflow.

However, I don’t think it is necessary. As long as you regularly clean the original AC filter and thus, maintaining a good airflow rate, dust built-up is inevitable but very slowly. Some buildings only need to do duct cleaning after more than 10-15 years of 24/7 usage.

I also heard some people said that they have pets and they saw many hairs go inside the return vents. However, don’t worry about it, the hair will be captured by the original AC filter. It’s just that you have to clean the filter more frequently.

How About Filters on Supply Vents?

You should not put filters on supply vents because it does not help anything but reducing the airflow of your air conditioner and thus, causing problems such as insufficient cooling and condensation.

AC filters are meant to protect dust from entering into the cooling coil and clog it up. Putting filters after the cooling coil does nothing to protect the coil. It only blocks the airflow which is bad for the performance of the air conditioner.

Conclusion

If I were you, I’ll crank my head to solve the accessibility issue so that I can take out, wash and put back the original AC filter. The filter is most compatible with the air conditioner. Thus, I can have peace of mind as long as I wash the filter regularly.

Putting multiple return vent filters is just too much inefficient work for me. Air conditioners are not designed in such a way. Furthermore, if you have a fresh air intake, more work has to be done.

Nonetheless, there are times when putting filters on return vents is necessary. Just like my previous work on a very old building. We had no choice but to put hundreds of return vent filters. Trust me, it is a painful process. Anyhow, everyone has a different situation, do what is best for you and know what to expect.

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Yu Chang Zhen

Yu was working in the air conditioning industry for the past 7 years, covering from design to installation and maintenance. Yu wish to share all the things he learned with the people around the world.

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