Best MERV rating for HVAC air filter?

naivehomeowner

I have a Ducane air handler about four years old that works central air conditioning for cooling and a hydro coil for all the heat in the space. Other than recommending that the air filter be changed regularly the air handler owners manual does not specify the filter MERV rating. I have read a lot of contradictory advice about best MERV, some says higher is better air filtration for example that MERV13 should be used to filter out virus. Other advice states that high MERV is bad for the system and will reduce efficiency and wear out handler motor thru excessive air resistance. I have two big dogs that shed a lot and another dog and cat, and the space includes kitchen so I like the idea of maximum air filtration but certainly don’t want to burn out the handler motor prematurely. The filter is 24x16x1 inch. What is best MERV rating and does that change according to whether it is cooling or heating function? thanks for any advice

SlamDunk

I wouldnt go crazy with the higher filtration. They will clog with fur faster and become even better filters; and, your airflow will be reduced. But if you replace filters frequently, go for it.

pecmsg

MERV rating is one thing. You need to know what the static pressure is on the system.

I say go with the lowest MERV rating. The filter is to protect the equipment, not vacuum the house!

Zman

If you want to go with a higher rating, you will need to do some homework. The higher the MERV, the more filter changes you will need, a lot more. Using too fine a filter could also reduce the airflow to the point where your system will malfunction or be damaged.

naivehomeowner

As for using lowest rated MERV, I also read that higher MERV can prevent fine dust from building on hydro coil fins and that is a consideration?

Zman

I am sure the finer filter will reduce that dust as well. Another avenue you could explore would be to go with a deeper filter. Deeper (thicker) filters have more surface area and would overcome some of the extra resistance associated with the higher merv.

naivehomeowner

The filter space only is for one inch depth.

Zman

naivehomeowner said:

The filter space only is for one inch depth.

Does it have to stay that way? You can likely make it bigger.

HVACNUT

I don't think you'll find anything above a MERV 8 with a 1 inch filter anyway, and that's fine.
If you're concerned about allergies and stuff, you could look into UV lamps or an ionization generator. 
If the house is dry, a whole house steam humidifier like the Aprilaire 800 will help during the heating season. 

ChrisJ

HVACNUT said:

I don't think you'll find anything above a MERV 8 with a 1 inch filter anyway, and that's fine.
If you're concerned about allergies and stuff, you could look into UV lamps or an ionization generator. 
If the house is dry, a whole house steam humidifier like the Aprilaire 800 will help during the heating season. 

Oh yeah, you can find them.
I recall seeing alleged MERV 13's in a 1".

If it was my system and I insisted on using a 1" filter I'd probably use the low MERV (3?) fiberglass mesh ones.

I run a 5" thick MERV 8 Airbear filter on my A/C.

PC7060

I've found the 3M Filtrete Basic pleated offer best performance without driving up the status air pressure drop across the air handler. The pleated filter will catch fine dust with potential for clogging (drywall dust especially) so be sure to check it monthly.

Looks like a MERV 5 rating

You can buy at both Home deport and Lowes

https://www.lowes.com/pd/Filtrete-3-Pack-Basic-Pleated-Common-20-in-x-20-in-x-1-in-Actual-19-6-in-x-19-6-in-x-0-8125-in-Pleated-Air-Filter/3800427

lkstdl

You can certainly use MERV-13 filters on your system but you will need to more filter area to avoid excessive pressure drop. The rule of thumb is Filter Area = 2 square feet (or more) for each 400 cfm of air flow. I'm guessing your system is in the 1600-2000 cfm range, so you would aim for 8-10 sq ft. filter area.

More information: Low Pressure Drop Across a High-MERV Filter

It may be easiest to switch to return filter grilles (individual filters on each return) rather than a single filter just before the air handler. These simply open up to allow you to replace the filter inside. They have the added benefit of keeping your return ducts clean.




There are filter grilles that will accept 4" deep filters (e.g. Hart-Cooley, Dayus) but they are les common than 1" or 2" depth versions. If all you can find are the 1" grilles, there are special deep filters that fit in a return grill made for 1" filters but I am guessing they'd be more expensive and harder to source than standard filters.