On Mon, 21 Nov 2005 16:46:23 GMT, "Rick Brandt"
wrote:


That would actually make it clog up twice as fast. To make a filter last longer
you need more surface area. Making the filter twice as thick does not add any
surface area.


Oh yes. Doubling the thickness does increase the filter surface area.
It also increases the air resistance to recirculating air and that may
reduce hot air reaching registers further away from the furnace. You
probably won't lose the total amount of heat output from the furnace.
I think having the filter clog faster might be a desirable result as
one can throw away a clogged filter and thereby permanently remove the
dust from the circulating air. In fact I think I will do this, cut
the hammock type filter to increase the regular filter's
effectiveness(?)