Furnace filter size

My in laws furnace call for 2 filters 16 X 16 X 1 inch and they bought 16 X 16 X 2 inch.
My question is, will the thicker filter cause a problem with the air flow?

That’s like asking… “My inlaws purchased a new car with air conditioning. Can they run E-85 fuel in it”?

Need more info!

(Begin with reading the users manual).


How would it be any thicker? 2 filters 16 X 16 X 1 inch = 2 inch and they bought 16 X 16 X 2 inch.

Usually when two filters are required they’re installed in 2 different places, but I’m* sure *you know that.


   I believe what you are asking about is the "MERVE-RATING". The higher the MERVE-RATING,  the more restriction to the air-flow. The lower the MERVE-RATING,  the less restriction to air-flow.

Check the filter Dave and see if the MERVE-RATING is around 7, it should be close. Remember to have them clean and replace per your recommendations.

In short, there really isn’t a big deal if the furnace keeps operating as it was intended. However when you go to your in-laws, listen to the system while you are carrying on a conversation. If you barely hear it running, they are fine. If the system seems a little noisier than normal, go back to the original filter size.

I agree … Roy … usually … no big deal

I believe that they will have to buy another filter as the furnace call for 2 filters…

Thickness should not be a problem if they fit.

Assuming the filters are identical when they install 2, I don’t think the second filter is accomplishing much of anything. If they were two different MERVE ratings it would make sense to line them up and each removes different sized particles of the dust in the air.

If the rating of the single filter is the same as the two, it shouldn’t cause any problem because it will have a larger surface area due to the deeper pleats. That should produce better air flow not less.


Some furnace (Dettson oil furnace comes to mind) require 2 filters to cover the area.

Ah… now we’re getting to the point of my comment of reading the users manual…

**What does the manufacture **recommend for filter(s)?

You may find that the manufacture recommends a two inch filter, but the prior homeowner took the cheap way out and installed doubled $0.59 cent filters as opposed to one $4.99 filter!

Also, I would NEVER install a newer HEPA type filter in an old POS furnace! Just asking for trouble.

There should little difference in airflow by going from one inch to two inch. If the furnace was that sensitive, it would constantly be locking out whenever the filter got dirty.

Thanks everyone.

Marcel, on this furnace the filters are installed in the shape of a V, they bought a case of 5 or 6 and I did put 2 new filters in.

Michael, I will check the MERVE rating out when I go over there later today.

Jeffrey, this is in a condo they just purchased and the previous owner didn’t leave any paper work for the unit…I guess I could have Googled it but you guys are more fun.

Thanks again and Happy Holidays.

Your post just proves my point… don’t you think all of this info would have been nice to have up front when asking the question? Perhaps you would have received more relevent information!

I’ll never understand why those posing questions on this MB feel it necessary to withhold information that the readers may find useful in attempting to help. It actually comes across as “playing games”, which I personally find distasteful. Many bi*ch and moan that this MB isn’t professional and always strays from the original subject, well… it all begins with precise, professional opening posts! Think about it.

I do not really understand this post as my HVAC requires 2 Filters side by side to fill the duct.
There is no room to double the thickness (4 Filters at a time)
more clarification and/or photos are needed…

May I ask what kind of trouble would you be referencing the old POS furnace blower motor has a RPM of 1500 RPM and the brand shiny new furnace blower motor has a RPM of 1500 RPM???:wink:

I was reading the OP wrong. It sounded like they replaced two with onepre filter and fine filter), not two with two thicker ones.

Gosh, that makes this a total non-issue. The thicker one has more surface area if the ratings are same.