Many forced air furnaces have throw-away type fabric filters. It still surprises me how often these filters are installed so that they can be drawn out of place by the suction created by the furnace blower. When this happens the filter can be sucked against one side of the blower. This condition allows all the air returning to the furnace to by-pass the filter and go into the other side of the blower where it is blown back through the supply air registers and into the house.
In my opinion these filters should never be installed "inside" the plenum immediately attached to the furnace----unless there is some means of "positively" holding all four edges in place. This is rarely the case. Usually there is some assortment of wires that hold it in place (or nothing at all) and the filter, under suction, deforms to allow air to pass unfiltered around the edges.
As the filter becomes clogged with dust, the blower has to work harder and shortens the blower's life as well. This picture shows a filter that has been sucked against the blower and the circular discoloration is dust that has been pulled through the filter. This is the "clean" side of the filter.
While I could go into how these things "should" be installed, a better solution is to upgrade to an electronic type air-cleaner. These cloth type filters, even when "ideally" installed, still do not clean the air the way an electronic filter will.
Charles Buell
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Hi charles, can you tell me where one can find out about the electronic air cleaners which you would recommend? Thanks.
Joan, I don't really have a "favorite" but I see lots of Trane and Honeywell
Charles, it is common practice around here for furnace installers to install the filters in the return air in a sort of slide channel. As long as the filters are changed regularly, and they are not the 'cheapest' kind you can buy, there isn't usually a problem with them sucking into the fan.
Sometimes they don't install a proper channel for them, as you say, and then they would get sucked in.
Also, in newer installations, if they don't have an electronic air filter, many installers are going to the wide filter media. These are much better, and more efficient, and not much chance of getting sucked in.
How am I supose to get any real estate work done if I have to keep running home to check systems evertime I read your posts? cheryl (hope mine doesn't ) willis
Kevin, I just like to see that channel on the "ouside" of the plenum that the blower is in so that it gets sucked against four flat surfaces.
Cheryl, you remember what Manard G Krebs said about "work"?:)
Even if there is the proper chanel the cheapo filters get sucked in over time (without the use of wire supports). The dirtier the filter gets the more chance there is of it becoming fan fodder.
Jack, when the filters get really plugged it can make the blower work too hard trying to pull air through the filter.
Charles, when I purchased my apartments many years ago EVERY furnace/AC filter has Soooo stuffed with dirt that it was about impossible for me to pull them out. We then had to go through every fan and scrap the layers of dirt off the blades. Took forever to clean them all, not to mention all the motors we had to replace.
Sean Allen
Sean, so much for having a maintenance plan in place:)
Good tips Charlie. I have seen filters that gagged me taking them out, all the dust in the air.
Choke.... call the paramedics! Whats even worse.... I have found that there were a couple of hvac companies in Cleveland that were installing funaces WITHOUT any return aire system at all, no filter, no ductwork. The poor fans were sooo caked that the "dust" frequently blew off into the ductwork in large chunks!
Unsuspecting homeowners didn't know any better... they were being sold as 'maintenance free' units that never needed the filter changed... imagine that.
Steve, like you say----they can be really nasty at times.
Kevin, permenant filters----now there is a concept that will sell:)