I live in the Pacific Northwest (Seattle area) and the allergy season has started for me. It is so bad that I am thinking about getting an air exchanger for next year. The house I live in was built in 2007. It has a standard gas furnace and the furnace has a large 20 x 25 x 4 filter attached to it (I change the filter twice a year).

What is the difference between the filter attached on my furnace and an air exchanger? Are they doing the same thing? Would I get much better air in the house with an air exchanger? Is it worth getting an air exchanger?

Thank you!

  • This is a pretty broad question as written. An air filter simply tries to catch dust and an exchanger actually takes new air from outside and puts that into your house. One is not a replacement for the other. You may want to do some basic research and focus your question more with any specific questions you have.
    – JPhi1618
    Apr 4, 2019 at 18:11

2 Answers 2


Do you mean HRV/ERV? They won't help with allergens. In fact they are likely to make the situation worse. Their job is to bring in fresh air and pre condition it with the outgoing air. They do have filters but they are just to protect the exchange core. If your allergic reactions are due to pollen and the like an HRV will make it worse as the equipped filter is not a MERV rated filter. You would be better off installing a whole house HEPA unit.

Duct mount HEPA

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Elecro-Air Five Seasons

I've installed lots of these. You would leave the furnace fan running constantly as well as the HEPA filter fan. There are much better options available from IQAir but they are very expensive.

  • MERV is the ASHRAE standard for filter performance. MERV 12 will capture 35% of the particles that are 0.3 microns, the HEPA standard is 90%, equivalent to MERV 16. There is debate among allergy specialists as to whether or not this ultimately makes much of a difference for sufferers, but I believe it helps.
    – JRaef
    Apr 4, 2019 at 21:50
  • I only install them on a request basis. I have zero allergies and can eat just about anything. Anytime I've put the HEPA units in I've always got very positive feedback. Could be a placebo. I don't have any tools to test how well they work. I just don't know.
    – Joe Fala
    Apr 5, 2019 at 1:08

Conceptually they are the same if you have a fan forced furnace, but not all furnaces are like that, some are passive (convection). But also, the filter on your furnace must allow the proper amount of air to pass through it based on the blower capacity and air ducting, otherwise your furnace efficiency drops and it costs you more to operate it. But you should be able to buy "hypoallergenic" filters for most furnaces, where they use highly pleated filter media to increase the total surface area in order to compensate for the lower air flow through the media. These filters will cost you a lot more than standard filters, upward of 10x the plain filter cost depending on what level of filtration you want.

With an air exchanger, flow efficiency is irrelevant so the filter can be more restrictive and can operate with a low air volume since you typically leave it on all of the time.

  • Thanks for the reply. I have a forced air furnace. If I understand you well, a $85 filter MERV 12+ would do the same job, right? If I was to get an Air Exchanger installed, would it use my existing duct?
    – Martin
    Apr 4, 2019 at 18:44

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