Filter Due

How it works

Your filter wears out while the blower runs. The blower runs when it is hot or cold outside. So we read your local weather, day by day, and add up the wear.

Cold days (below 62 °F average) run the furnace. Hot days (above 72 °F) run the AC. The further from that band, the longer the blower runs, up to about 17 hours a day. Mild days still count a little: dust settles and the fan cycles.

A 1-inch filter is rated for about 90 days at 8 blower-hours a day. Thicker filters last longer. Pets, allergies, smoking and dust shorten the life. And no filter should stay in past its maximum age (1": 4 months, 2": 6, 4": 9, 5": 12) even in a mild climate.

No change logged? We count backward from today until one filter's life is used up. That date is your line: changed before it, the filter is due now.

Change logged? We count forward from that day. Past days use measured weather, the next 16 days use the forecast, and later days use last year's weather for the same date.

This is an estimate. A filter that looks gray or clogged is due, whatever the date says.