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Need rec: Furnace Filter for cat hair
QUESTION:Would someone in the know please advise me (a homeowner) on the selection
of an appropriate high efficiency furnace filter? I am concerned about
the potential over-heating of my heat exchanger if I use an inappropriate
filter. We have a 2-year old gas forced air Lennox (sorry, but don't have
the model number here, but I recall it's rated at 90% efficient) vertical
draw, and I think the filter is 18 x 25". We have *too many* cats and our
present filter (Whistle-Air) gets pretty choked with cat hair as well as
dust. I'm pretty good about cleaning it every month, but I'm concerned
that even when it's clean it's too restrictive to air flow since the
furnace will run for a while and then turn off *before* reaching the room
temp the thermostat is set for. When we had it serviced this fall it
'passed' with flying colors, and no criticism was made about the filter.
I presume that there's a calculation that can be made, but are filters
*rated* as to air resistance? Alternatively I suppose that air pressure
could be compared on either side of the filter, but this is probably
beyond what I could/should do.
Of course, what I'm hoping for is someone to tell me, "Oh, just buy the
'Filter-Gizmo' brand -- they work in everything." Actually, I've seen
some of the plastic electrostatic filters and they obviously might work in
anything, but with their coarse mesh and lack of a fine-pored medium, are
they actually filtering much of anything? If I get a permanent filter
it's important that I'm able to dislodge the 2" long cat hair that tends
to 'weave' itself into the Whistle-Air.
ANSWER: The best way to tell if you're creating a problem is to check your heat
rise. To do this you'll need a small dial thermometer. Look on your
furnace data plate. Someplace it will mention temperature rise. It's
usually in the range of 65-90 degrees F. I have seen a couple that
specify a maximum outlet temp. To check the temp rise drill a small
hole in the supply trunk out of line of sight of the heat exchanger.
This is important so we don't get radiant on the thermometer probe.
Also drill a small hole in the return near the furnace. Measure the
temp at these points while the furnace is near normal operating
temperature. The difference between these readings will give you
temperature rise.
Is the furnace shutdown a new problem or has it been that way right
along? Is the burner only shutting down or blower and burner?
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