Write the install date on your furnace filter
Furnace filter
Mark the install date on the cardboard frame edge with a permanent marker so you can peek and know when the HVAC filter was last changed.
A clean-looking filter can still be months old. Writing the install date on the cardboard edge turns the next peek into a calendar check instead of a guess.
Mark the frame once
- After you seat a new filter (size and arrow first — see Read furnace filter size before you buy and Furnace filter arrow must face the airflow), use a permanent marker on a visible frame edge.
- Write the month and day (and year if you like). Leave the date where you can read it without fully pulling the pad.
- Optional: set a phone reminder for a rough check — many homes peek at a 1-inch filter every 1–3 months, sooner with pets or heavy dust. Gray, packed pleats beat the calendar; if you cannot hold light through the media, swap it.
If a new pad whistles, reseat or check density with Furnace filter whistle after a new filter instead of waiting for the reminder.
Honest stop
Never run the system with an empty filter rack “until the next delivery.” Dust loads the blower. Cabinet work beyond the filter slot is HVAC territory.
More help
- Same niche: Furnace air filter — do not crush accordion into a thin slot · Furnace air filter — cut-to-fit foam is not a pleat · Do not wash a disposable furnace air filter · Furnace filter arrow must face the airflow · Furnace filter whistle after a new filter · Furnace air filter — seat toward the hinge-side slot wall · Furnace air filter — lifetime labels still mean replace on schedule · Furnace air filter — measure slot depth if the size stamp is gone · Furnace air filter — metal-mesh vs electrostatic washable labels · Furnace air filter — photo the size stamp before you discard it · Read furnace filter size before you buy · Furnace air filter — return-grille foam is not the slot filter · Furnace air filter — skip high MERV when return grille foam already blocks · Furnace air filter — slide it flush to one slot wall · Furnace air filter — store the spare flat and in plastic · Furnace air filter — tape a faded airflow arrow before you install · Tell washable vs disposable furnace air filter · Furnace air filter — check it sooner if the fan stays on · Furnace air filter — tissue test register airflow after a swap · Furnace air filter — turn the system off before you swap · Furnace air filter — vacuum the return grille at each swap · All furnace filter guides
- Related fixes elsewhere: Dryer takes two cycles — vent checklist · Leave clearance so the dryer hose is not crushed