Dear Comfort Advisor,
I just got a bid to replace my furnace and it was suggested that while the return duct was being modified, it would be a great idea to install a wide filter box, is that really necessary?
Dear Freddy with a Fancy Filter,
It is indeed true that there are quite a bit of filter options available for both new systems and existing furnaces. I have certainly seen an ever increasing trend in both residential and commercial systems that have enhanced filtration. The standard 1’’ filters have been the mainstay for years but are limited as to their effectiveness and service life. Many companies have developed better filters to fit into a 1’’ slot. These designs have met with mixed reviews because they have built-in limitations mainly because of the size constraints.
The circulating blowers on just about any forced air unit, be it a gas furnace or heat pump, are designed for a certain amount of restriction inherent in a filter. This is measured in inches of static pressure with a magnehelic gauge. A glass-floss fiberglass filter you can see through obviously has very little restriction because it is really nothing more than a screen. Pleated filters are a much better choice for air filtration but put more restriction and thus reduce airflow through the furnace. Many people have purchased “electrostatic filters” which induce a static charge as the air is pulled through the filter media. Many were built with multiple layers of material like a charcoal sheet for odor. This design not only stopped particulate which is good but seriously restricted the air flow through the system which is very bad. Imagine how hard your heart and lungs would need to work if you had to breathe through a pillow all day. Many heat exchangers have had shortened lives because of this type of filter.
As described above a 1’’ filter slot puts limits on the effectiveness of filtration. Enter deep pleated filters. In a pleated filter, the media is accordion folded like those paper fans you made in elementary school. 2’’ pleated filters have been used in commercial equipment for decades. They have a longer service life, less restriction, and more effective filtration. The increased surface area of a deep pleated filter media actually reduces airflow restriction. This design has been improved upon to the point that four and five inch width filters are becoming the norm in residential applications. There is a Lennox MERV 16 filter that has over 45 feet of filter media in a five inch wide slot. This is amazing and so is the benefit to the homeowner. For those who have electronic air cleaners, most manufacturers produce deep pleated filters that fit into the same housing.
This reduces maintenance and is actually more effective. For crawl space applications it is mandatory in my opinion to use deep pleated filters for nothing less than having to go down there only once a year. They also have sealed gasketed covers which eliminate sometimes questionable air in the crawl space from being introduced into the home. We are becoming accustomed to minimal maintenance and changing furnace filters every 1-2 months just doesn’t seem to happen and leads to furnace breakdowns. More furnaces are damaged and made inefficient by running dirty filters than any other every service issue. The proper application of deep pleated filters will keep the air you breathe cleaner, be easier on your heating and cooling system, and reduce maintenance on the equipment. I can review your particular situation and find a suitable filtration system to meet your needs and your budget. As always estimates and good advice is free at AirWorks.