Air filters

[jacount]

Hello all, I have recently discovered the Honeywell FC40 filters that let you put a thicker filter in a return box than what they normally can handle.

My question, is which would be better, the 20x20x1 MERV 13 filter that I have now, or an FC40 that is 20x20x5, but only MERV 10 or 11?

How can a 1" filter be better at filtering air then the much bigger FC40? What am I missing?

[jtrammel]

The 5" will be better, as long as the filter box is deep enough to accept the filter without choking off the air flow. The 1" filter is very restrictive and can cause problems with the system.

[jacount]

The 5" will be better, as long as the filter box is deep enough to accept the filter without choking off the air flow. The 1" filter is very restrictive and can cause problems with the system.

Better for the system, or better air filtration?

There is a good amount of space behind the filter but unfortunately the duct comes in at the bottom.

I like having MERV 13 filtration as I do have allergies, but I can't fathom that the 1" MERV 13 can really filter more then a 4 or 5" filter.

That said, when I replaced the existing paper thin fiberglass filter to the MERV 13 one, it was saturated with dirt in less then a month.

[RACMT]

Air Filters are rated by MERV > Minimum Efficiency Reporting Value, When you think of a air filter and you can't seem to fathom why it is than think of it like this:

You have a 5 gallon pale filled with water and you have to fill a 5 gallon pale that is underneath it and you poke one whole that is 1/4 inch in diameter and you let it drain. ok this is you 1 inch pleated 13 MERV

Now say you have a 5 gallon bucket filled with water and you have to fill the 5 gallon pale underneath it sbut this top pale with water in it has 10 holes at 1/4 inch in diameter. it will fill the pale faster because even though all the holes are the same size there is more of them so this is like a MERV 13 5-6 inch pleated.

So what we have here is a fixed value

our return air drop is x and say we don't want to change the size

Our desired CFM for Air Conditioning is 350 - 400 CFM per Ton of cooling

On the average system we have a TSP Total Static Pressure of .5 inch W.C

So if we desire MERV 13 filtration which is has a 90% Dust Spot Efficiency, So the more dust at smaller particle size and more efficient at arresting these particles brings me back to my 5 gallon pale example.

You can buy a 1 inch 13 merv which will choke your system and cut down on system capacity and performance or you can install a 5-6 inch pleated filter which has more surface area to allow to have small holes to arrest small particulate but at the same time allow for a lower pressure drop in the system.

The only reason companies sell these 1 inch hi merv filters is because they realized they can charger 10 times more. At the the end of the day 1 inch filters that are standard on an air handler system were never designed to clean the air, they were only designed to protect the coil from larger dirt and debris that could quickly plug up the indoor coil and now more importantly the secondary coil on Hi Eff furnaces.

If you have allergies and you have the money than put in a whole house HEPA by pass air cleaning system.

Another thing to remember is that no matter how efficient your filters are they can't suck the dust off the furniture that is the number one complaint by HO...

[jacount]

Thanks! I think I understand.

Unfortunately I'm renting so I can't put in a better filtration system, but I will most likely get the thicker FC40 filters to replace the MERV 13 I have now.

Is the 20x20 return thats there even big enough for the 2.5 ton HP that's installed?

[RACMT]

If you are renting and you are concerned about allergy mediation then the best bet is to invest in a portable room air purifier that way you don't put money into improving your slumlords equipment and if you ever want to move you can just bring it with you. I put MERV 8 in my stuff just sayin. My wife and son have allergies but I came to the conclusion that no air filter will stop them from having allergies.

[dlove]

AIR IS EVERYTHING the more efficient a filter is the higher the static will be, as its gets dirty static rises restricting air movement. before spending $ on expensive filters understand how it effects your system, Just because a filter looks dirty it may be working fine. I tell people to get a decent filter have someone check static and check it over and over as it gets dirty..go buy a manometer and check it yourself, it will pay for itself. knowing how dirty your filter gets and how fast is critical. you may need to change it once a month or one every three months..lastly i would recommend a portable air freshener.

[jacount]

I actually decided to buy a normal 5" merv 13 filter and let it stick out from the housing. I was afraid there wasn't enough room behind the fc40 types because the flex duct connects to the filter box from below.

[Ben14]

I second the idea of the room air purifier. We have one in each room and they have helped my allergies quite a bit.