Customer Q & A
Q1: My furnace can accomodate either a 4in. filter or a 1 in. Could I use two filters or would this harm the unit by overly restricting airflow? If I can't, which is better the 4in with a 1550 MPR or a 1 inch with a 1900? I noticed the 1inch only captured 93% while the 4inch said 97%. Being allergy free is more important than cost.
I'm not exactly sure since I don't know the specifics about your furnace airflow, how large is the unit, how many rooms in the home, how many floors, etc., but I would recommend going with the 4" filter. While doubling the 1" filter would improve filtration, you're still going to have more filter media with the 4" filter.
The 1" filters have much tighter pleats, and I think you are right to worry that doubling this may put too much strain on the blower.
Q2: How often do these filters have to be changed? If I use a media filter, does that eliminate the need for other thinner furnace filters?
Typically, the 4" media filters last you 1 year, so replace annually. This may vary a bit depending on the conditions in your home and where you live. Areas effected by high levels of seasonal pollen may decrease the filter life.
Generally, no, a 1" filter is not required. Most often large media filters like these are used in commercial settings where air is circulated through much larger spaces than the average home. So these thicker, larger, higher capacity filters are ideal in those situations. In commercial applications these filters are changed more frequently, but in a single dwelling, you should only need one filter per year to keep the air freer of dust, dirt, and other particles.
Q3: What is the MERV rating for your Filtrete 1550 Allergen High Performance Filter 20x25x4. Thank you
MERV ratings measure filtration efficiency of particles ranging from 0.3 microns and up. With more an more emphasis being placed on micro particles, 3M developed their MPR Micro Particle Rating to measure filtration of even smaller particles, down to .001. Some competitors are beginning to adopt the new standard that 3M developed but there is still predominant use of MERV.
As a reference, the 3M Micro furnace filters have a MPR of 1000. Their rough equivalent MERV rating is 13-14. So while their is currently no sure equation way to convert MERV to MPR, if you use the approximate MERV rating of the Micro filter MPR rated at 1000, then the 4" filters MPR rated at 1550 would conceivably exceed MERV 18, which currently puts their filtration in line with the more expensive NordicPure furnace filters.
Because 3M uses this different measuring scale and system, it's difficult to do a straight comparison.
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