Furnace Filter Airflow Restrictions

[Buzz]

I've consulted several HVAC contractors on this subject and received widely ranging answers so I've turned to you folks for some expert opinion/help.

I currently use 3M's new 12 MERV 1" premium filter and my furnace fan is set to 'auto'. I'm very satisfied with the filtering I'm currently getting with this filter. I'm in the process of adding an HRV and will

be running the furnace fan on low at the continuous setting year-round.

Some contractors have suggested upgrading from a 1" media filter to a

5" media filter to improve airflow, theory being the 3M's I'm currently

using are too restrictive now that I'll be running the fan continuously.

My concern is that the 5" media filters typically have a lower MERV rating and I'll lose some filtering effectiveness.

Should I be concerned about airflow restriction with the 3M filters based on continuous fan operation and is there any other benefit, aside

from reduced filter change frequency, to switch to a 5" media filter?

The one upside that I've considered is that if I add a 5" filter to my system I can use the 1" slot for a charcoal/carbon filter to improve odor/gas removal - any thoughts?

I appreciate your responses. Regards. Buzz

[m Ransley]

I have an april air media , its a good filter and it lasts, filter efficiency goes up as they get dirtier a large media will do a better job longer. Just dont get an April Air unit the casing design leaks air past the filter housing, something an april air rep said cant be fixed.

[Tony Hwang]

Huh? The better, the dirtier?

[Bob]

[Bob]

If you look long enough, you'll find people to tell you how great those filters are, but I've seen them do more harm than good.

[Stretch]

The April-Aire filters have a high MERV, 12 as I recall. They have MUCH less restriction to air flow than the one inch pleateds. Up to

2.5 tons, the April-Aire filters are about the same pressure drop or less as a properly sized fiberglass filter. The one-inch pleated filters have about 2.5 times the pressure drop of a properly sized (or same sized) fiberglass filter. This is according to my own testing with an air flow hood and digital manometers and magnahelic gauges. If you put a carbon filter in the 1" slot, plus have the Aprilaire filter, your pressure drop will go sky high again. Typically, a 1" pleated filter will drop air flow 10% to 20% vs. a standard fiberglass filter. If you want all that filtration, have someonme measure your air flow with a flow hood before you install the filters. If you have less than 400 CFM/ton, stick to a fiberglass filter OR upgrade to a variable speed blower OR replace your duct system. Low air flow will reduce your system capacity efficiency and capacity. It can also damage your compressor.

Stretch

[m Ransley]

Learn bobb, go read the April Air site. Filters filter better the dirtier they get, filter dirt better. A filters job is filtering dirt while allowing suficient airflow required for proper furnace operation. The % pass through of dirt continues to go down till they are restrictive, needing replacement. April Air Media go up something like

9% as they approach needing replacement. Media filter different micron size particles at different first time % pass through. First time % pass is the important number I am refering to, not airflow which large media are superior in compared to 1". As acumulations of dirt build on the filter first time % dirt pass through efficiencies go up on media, less dirt is passed though. It is what media do, nothing new. Airlow is not comprimised enough requiring replacement till filter is dirty. This is exactly the oposite of 120v powered electronic wire type, they need to be clean to meet stated efficiencies.

So bobb learn a bit before you post a response.