OT: HVAC Air Filters, Detrimental If MERV Too High?

dbCooper

Approximate 10 year old multistage Rheem Air-Source Heat Pump with natural gas backup.

Have always used 3M 1200 Filtrete filters with a MERV of 11.  Costco has been out of stock lately on my size, 20x25x1.  They have a Kirkland 2200 hi-perf filter in stock, MERV is 13.  I'm hesitant to buy these for a couple reasons:

- I get that the more efficient filter will reduce air flow and make the system less efficient.  Not a big concern.

- Seems the less efficient system may be damaged due over-stress from the reduced air flow. 

The second point is what I'm looking for help on.  Is that a valid concern and enough to stay away from a MERV 13 filter?

The Rheem manuals highlight the importance of filters but don't address which MERV to use/don't use.

Thanks for any insights on this.

Canugghead

tbh, I've no idea what MERV means  on a somewhat related note, I just bought two of these Winix units, you may find some useful MERV info in this discussion...
https://forums.redflagdeals.com/costco-winix-c535-air-purifier-159-99-40-off-2592480/

lkapigian

It’s not the MERV is to high, your return is grossly undersized , I am a fan of high MERV filters on duct systems we design and install, on others , use cheap low MERV filters … 20x25 is good for a 2 Ton AC or 800 CFM ( free air in the grill size) the other looming issue is the duct size from the grill to the unit . Delivered air= Delivered capacity 

CFM x Delta- H x 4.5. = total delivered capacity ( sensible + latent)

on another note, filters really just protect the equipment and do next to nothing for IAQ

kl8ton

lkapigian said:

It’s not the MERV is to high, your return is grossly undersized , I am a fan of high MERV filters on duct systems we design and install, on others , use cheap low MERV filters … 20x25 is good for a 2 Ton AC or 800 CFM ( free air in the grill size) the other looming issue is the duct size from the grill to the unit . Delivered air= Delivered capacity 

CFM x Delta- H x 4.5. = total delivered capacity ( sensible + latent)

on another note, filters really just protect the equipment and do next to nothing for IAQ

Pfffft.  Could we please get someone in here that knows what they are talking about?    

dbCooper

lkapigian said:

It’s not the MERV is to high, your return is grossly undersized , I am a fan of high MERV filters on duct systems we design and install, on others , use cheap low MERV filters … 20x25 is good for a 2 Ton AC or 800 CFM ( free air in the grill size) the other looming issue is the duct size from the grill to the unit . Delivered air= Delivered capacity 

CFM x Delta- H x 4.5. = total delivered capacity ( sensible + latent)

on another note, filters really just protect the equipment and do next to nothing for IAQ

@lkapigian - The furnace is a Rheem RGPE-07EAMKR with cased coils RCFL-HM2417CC.  Am I reading your response correctly, my return duct work needs enlarged to accept a filter bigger than 20x25?

lkapigian

dbCooper said:

lkapigian said:

It’s not the MERV is to high, your return is grossly undersized , I am a fan of high MERV filters on duct systems we design and install, on others , use cheap low MERV filters … 20x25 is good for a 2 Ton AC or 800 CFM ( free air in the grill size) the other looming issue is the duct size from the grill to the unit . Delivered air= Delivered capacity 

CFM x Delta- H x 4.5. = total delivered capacity ( sensible + latent)

on another note, filters really just protect the equipment and do next to nothing for IAQ

@lkapigian - The furnace is a Rheem RGPE-07EAMKR with cased coils RCFL-HM2417CC.  Am I reading your response correctly, my return duct work needs enlarged to accept a filter bigger than 20x25?

Since it’s only a 2 ton ( 800 CFM) 20x25 is right there , you want .5” “ per CFM Free Area, so you have to account for the louvers , if you want to use high MERV , I would go no less than 20x30 and a duct area of at least 320 square inches …. The only way to really know your system is to measure the static pressure and go from there 

But to your original question, high MERV filters are detrimental to the equipment if not done properly, these stores make a ton of money selling them without any thought to performance 

Legume

.

nolaegghead

Efficiency be damned without enough filter area to lower the static pressure to get the factory flow rate, EXCEPT if you are running a gas or electric furnace where it makes little difference (maybe some with gas).  But I digress, you have a heat pump.

nolaegghead

Anyway, @lkapigian is the master of HVAC, he has saved me a ton of money through the years when my stuff breaks.  (because I can fix it myself).

dbCooper

lkapigian said:

dbCooper said:

lkapigian said:

It’s not the MERV is to high, your return is grossly undersized , I am a fan of high MERV filters on duct systems we design and install, on others , use cheap low MERV filters … 20x25 is good for a 2 Ton AC or 800 CFM ( free air in the grill size) the other looming issue is the duct size from the grill to the unit . Delivered air= Delivered capacity 

CFM x Delta- H x 4.5. = total delivered capacity ( sensible + latent)

on another note, filters really just protect the equipment and do next to nothing for IAQ

@lkapigian - The furnace is a Rheem RGPE-07EAMKR with cased coils RCFL-HM2417CC.  Am I reading your response correctly, my return duct work needs enlarged to accept a filter bigger than 20x25?

Since it’s only a 2 ton ( 800 CFM) 20x25 is right there , you want .5” “ per CFM Free Area, so you have to account for the louvers , if you want to use high MERV , I would go no less than 20x30 and a duct area of at least 320 square inches …. The only way to really know your system is to measure the static pressure and go from there 

But to your original question, high MERV filters are detrimental to the equipment if not done properly, these stores make a ton of money selling them without any thought to performance 

@lkapigian - Thank you.  I'll stay away from the higher MERV  and wait for 3M 1200's to get restocked.  Looks like Sam's Club is currently out of them too.

dbCooper

nolaegghead said:

Efficiency be damned without enough filter area to lower the static pressure to get the factory flow rate, EXCEPT if you are running a gas or electric furnace where it makes little difference (maybe some with gas).  But I digress, you have a heat pump.

@nolaegghead - My heat pump is air sourced, if temp gets colder than about 25 degrees the gas furnace takes over.  Hindsight says I should have gone ground sourced.

lkapigian

dbCooper said:

nolaegghead said:

Efficiency be damned without enough filter area to lower the static pressure to get the factory flow rate, EXCEPT if you are running a gas or electric furnace where it makes little difference (maybe some with gas).  But I digress, you have a heat pump.

@nolaegghead - My heat pump is air sourced, if temp gets colder than about 25 degrees the gas furnace takes over.  Hindsight says I should have gone ground sourced.

Hybrid heat is the way to go, ground source ( IMO) cost benefit ratio is low, the new heat pumps HSPF ratings are excellent below 0 c

lkapigian

 But I did stay at a Holiday Inn Express last night 

stv8r

I have to respectfully disagree with some of the information in the above posts.  A 20x25 return is good for a 3ton unit all day long.  1200cfm at .10 static pressure (recommended residential setting).  Your 2ton AC only requires 800 CFM.  A 30x20 rates at about 1500 CFM so total overkill.  However too big of a return is never an issue only  too small can cause problems. I am assuming your filter size matches your return duct size. The air filter is designed to protect the system from large particulates not improve air quality as some mentioned and a low MERV filter does that just fine.  A high efficiency filter can tax a systems airflow when it gets loaded up as most people don't change them often enough.  I'd go with the lower efficiency filter and change it once a month whether you think it needs it or not.  Cheap insurance.  

FanOfFanboys

I just buy the absolute cheapest filters and replace them 1st of every month. Is that wrong?

lkapigian

@stv8r design static is 5 not point 1 and most systems hover closer to .7-1 

lkapigian

FanOfFanboys said:

I just buy the absolute cheapest filters and replace them 1st of every month. Is that wrong?

Not at all

lkapigian

lkapigian said:

@stv8r design static is 5 not point 1 and most systems hover closer to .7-1 

Edit .5 not 5 

MaskedMarvel

I go through this a lot with my hvac folks. 

They’ll test the load with a simple service call, and be able to tell you  if your system is overloaded. 

stv8r

lkapigian said:

@stv8r design static is 5 not point 1 and most systems hover closer to .7-1 

then why does the duct calculator say the recommended setting for residential is .1? 20x25 is one of the larger return sizes in residential, definitely not just for 2 ton

lkapigian

stv8r said:

lkapigian said:

@stv8r design static is 5 not point 1 and most systems hover closer to .7-1 

then why does the duct calculator say the recommended setting for residential is .1? 20x25 is one of the larger return sizes in residential, definitely not just for 2 ton

That’s friction rate, not static pressure 

I would never put that size on a 3 ton, nor 2 knowing I was going high MERV , which is where people run into trouble, fine on a 2 ton, but add the static of a high MERV or under sized return it won’t perform .

on another note, the old PSC motors did not mind the excess static in old undersized systems, they simply delivered less air and no one knew ( yes most hvac systems are oversized and under perform) the new ECM motors hate static and will fail prematurely every time, we typically can decrease system capacity, increase ducting and the system will out perform the old one at a much reduced KWH consumption 

You have to do the math on the whole system, not what a grill/register could/ would do in a perfect world