On 9/30/2015 11:15 AM, Bill Gill wrote:
Everybody says to inspect your furnace filters, but they don't say what to look
for. On the TV news they always say it, then show a filter that
is completely clogged. Obviously they should be replaced before that.
So what should I look for to decide if I need to replace them. I have
been replacing them every 3 months, but when I do I can barely tell
the difference between the old ones and the new ones.

We buy the cheap(est) -- DIRT cheapest! -- filters and try to replace them
monthly. We tend to have a fair bit of dust/dirt from the climate in
which we live so they get "visibly dirty" pretty quickly.

Our thinking is that it's easier to remember to do something (trivial)
every month than to keep track of N month intervals.