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Originally Posted by blade5009

How do you post questions on this site?

Go to the forum that that its description fits your question.
Click on new thread.

Type in topic.
Then type in question.
Then click submit new thread.

Honeywell makes a PD monitor.

Originally Posted by beenthere

If your waiting until they bow, your waiting TOO long!

Good.
So, bowing (regardless of appearance or being able to see through it) indicates resistance to air flow and so it must be clogging up?

Maybe somebody makes a furnace filter monitor based on pressure differential, light passing or the element being gradually bowed over time.
Is the ultimate pass/fail standard the upstream/downstream pressure ∆?

If I never replace a filter, the airflow will tend toward zero and the furnace high limit switch will open, yes?

Originally Posted by blade5009

How do you post questions on this site?

The same way I do. . .

How do you post questions on this site?

If your waiting until they bow, your waiting TOO long!

let me rephrase. . .

If they still look fine and are not bowed after 6 months and you can still sort of see through them, is there any reason to replace them? How 'bout after 12 months?
Do filters clog up even if they look perfectly OK?

every three months

Originally Posted by WhoIsThat?

After two months they still look almost new.

Then change them after 3 months. This is what I do, but I have no issues with poor air flow. I use the NaturalAire Standard pleated filters, MERV 8. The filter media is charcoal grey when I pull it out to be replaced (white when first installed).

Take care.

Originally Posted by grasshopper

Just change them monthly.

After two months they still look almost new.

Just change them monthly.

HD 16x25x1 paper frame furnace filters

Any suggestions on when to replace these, based on appearance or how bowed they become over time, or how well they pass light?

It seems to me someone made an embedded whistle for filters of this type that would start to whistle when the upstream and downstream pressure delta was enough. Anyone know of a company that makes these?

Thanks.