Envirosept Furnace Filter
I am in the process of adding central air to an existing furnace system. The system currently includes a Honeywell electronic air cleaner made in 1976. As part of the addition, I am considering replacing the old Honeywell with an Envirosept Electronic Furnace Filter, which sounds pretty good just from browsing the Net. My question is, would this new unit be much more effective (or less effective) than the old one? I know the old one is working to some extent, since I can see the dirt come off when it gets cleaned. Any advice greatly appreciated!
Answer:
Media air filters typically filter the air better than standard fiberglass filters. However they have much more resistance to air flow than standard air filters. Typically, they reduce measured overall air flow by 10% to 20%. If you add an AC coil to your existing furnace, you will be reducing air flow some with it. The electronic air filters usually have low resistance to air flow, I would stick with the existing electronic filter. Electronic filters are usually more effiient than media filters as well. Remember: Air Conditioning begins with AIR! supply and media, therefore produces o-zone as well high resistance media. The electrostatic filters typically used arrestance test for efficiency, which has a large particle size dust for testing. The media filters typically use dust spot test as opposed to arrestance test used by electrostatic filters. A 95% arrestance rating on an electrostatic filter is about the same as a 15 to 20% atmospheric dust spot test. The tests are completely different, therefore no direct co-relation. Electrostatic filters don't work well below about 300 Feet per minute air velocity, because they don't develope a charge below that air speed. Therefore their high resistance to air flow is their own enemy. If you oversize electrostatic filters to reduce resistance to air flow, the velocity drops below the 300 FPM threshold and they loose effectiveness. The combination filters like Envirosept and Dynamic are the worst of both worlfs. They have media which has high resistance to air flow needs and replaced periodically $$$, and they produce ozone. Nick, you should get a flow hood and a differential pressure gauge and test the results before you recommend them to anyone. The saving grace of the Envirosept is it seems to be a better than average filter, if you have a powerful enough blower to overcome their high resistance to air flow. As an option, put two filter grilles side by side, due to the fan laws, since the velocity is 1/2, the pressure drop will be only 1/4 (the square of the change). Then the Envirosept becomes a more interesting concept. Just remember, if you use a high resistance/efficiency filter, your air will be cleaner, but with reduced air flow your AC may not work well and your efficiency will be reduced. (Unless you have a high powered blower or oversized filter.) Nick, half of the systems that I measure have air flow of 200 CFM/ ton instead of the 400 CFM/ton they should have. Hence my dislike of high efficiency/high resistance filters that reduce air flow another 10% to20%.