Chapter 01Records · Practical note
How many air filters to buy for a year
Plan on 4 to 6 filters a year for each filter slot in the house. The EPA says manufacturers typically recommend a new filter every 60 to 90 days: a change every 90 days uses 4 filters a year, every 60 days uses 6. Two slots means 8 to 12. Check the filter once a month, as ENERGY STAR suggests, and change it sooner if it is dirty.
Source: EPA, Guide to Air Cleaners in the Home, checked October 9, 2026; ENERGY STAR maintenance checklist, checked October 15, 2026.
- Change interval manufacturers typically give60 to 90 days EPA, Guide to Air Cleaners in the Home, October 9, 2026
- Filters a year for each slot4 to 6 Arithmetic from the figures on this page
- How often to check the filterMonthly ENERGY STAR maintenance checklist, October 15, 2026
The arithmetic for one slot
The EPA says to replace filters according to the manufacturer's instructions, and that manufacturers typically recommend a new one every 60 to 90 days. The American Lung Association gives about every two months. A year has 365 days, so:
Source: EPA, Guide to Air Cleaners in the Home, checked October 9, 2026; American Lung Association, Air Cleaning, checked October 9, 2026.
- Every 90 days: 365 / 90 = about 4 changes, so 4 filters.
- Every 60 days, or about every two months: 365 / 60 = about 6 changes, so 6 filters.
- A plan in between, say every 75 days, lands on 5.
Count your filter slots
Multiply by the number of filter slots, not the number of furnaces. Filterbuy says larger homes often have more than one filter, and that equipment in an attic or crawlspace usually means several filters behind the return grilles instead of one at the unit. Walk the house with the system on: return grilles pull air in. Each one with a filter behind it counts as a slot.
Source: Filterbuy, Where Is My HVAC Air Filter?, checked October 9, 2026.
Two slots with two different sizes make two orders. A case of 6 in one size covers one slot for a year at the 60-day pace, or a year and a half at 90 days.
Let the filter tell you when
Treat the change date as a plan and look at the filter itself. ENERGY STAR's checklist says to inspect, clean or change the filter once a month. The EPA says that if filters look heavily soiled when you change them, change them more often. The American Lung Association suggests holding the filter next to a white sheet of paper to see how dirty it is.
Source: ENERGY STAR maintenance checklist, checked October 15, 2026; EPA, Guide to Air Cleaners in the Home, checked October 9, 2026; American Lung Association, Air Cleaning, checked October 9, 2026.
Heat pump homes may use more
Filterbuy notes that a heat pump air handler runs for heating and cooling, so its filter loads faster than the same filter in a furnace-and-AC home. If your monthly check keeps finding a dirty filter, plan for the 60-day end of the range.
Source: Filterbuy, Where Is My HVAC Air Filter?, checked October 9, 2026.
Thicker filters run on their own schedule
The American Lung Association's two-month figure is for the common one-inch filter that sits in the return ducts. Thicker filters in a media cabinet follow the interval printed on their own box or the cabinet label, so read that and put it in your record instead. Don't guess it from a 1-inch filter's schedule.
Source: EPA, Guide to Air Cleaners in the Home, checked October 9, 2026; American Lung Association, Air Cleaning, checked October 9, 2026.
Let the tool do the arithmeticHVAC filter size finder and replacement plannerEnter the date you put the current filter in. The finder gives the 60 and 90 day change dates, and the printable record keeps one row per slot.Example: 19.5 x 24.5 x 0.75 in (Actual size of a 20x25x1 filter)Open the tool
Buy and store the year's filters
- Order by the nominal size printed on the old frame. If it has worn off, the no-size guide shows how to measure the slot.
- Buy one filter to test the fit before you buy the year's supply.
- Store spares flat in their box. A bent filter won't sit snugly, and the EPA says a filter should fit without being bent or crushed.
- Write the install date on each new filter's frame as it goes in.
- Put the next change date in your calendar and on the record sheet.
Source: EPA, Guide to Air Cleaners in the Home, checked October 9, 2026; Filterbuy air filter size chart, checked October 9, 2026.
Checklist to print
Fill this in once, then reorder from it:
- Every return grille checked for a filter
- Number of filter slots counted
- Nominal size written for each slot
- Change plan chosen: every 60 days or every 90 days
- Filters a year worked out: slots x changes
- One filter bought first to test the fit
- Spares stored flat in their box
- Install date written on the frame
- A monthly check on the calendar
Tips and tricks
- Tip 01
Plan to the short end
Buy for the 60-day pace. If the monthly check shows a clean filter at 90 days, the spare carries into next year.
Source: EPA, Guide to Air Cleaners in the Home, checked October 9, 2026.
- Tip 02
Same day every time
Change the filter on the first of the month it falls due, so the date is easy to remember.
- Tip 03
Write the date on the frame
A marker date on the cardboard edge tells you at the monthly check how long the filter has been in.
- Tip 04
One size, one row
Keep a row per slot on the record sheet. Two slots of different sizes are easy to mix up in the store.
What we would do
Count slots, buy for six changes, check monthly
Walk the house and count every slot with a filter behind it. Buy 6 filters for each slot, test one for fit, and store the rest flat. Check the filter on the first of each month and change it at 60 to 90 days, or sooner if it looks dirty. Whatever is left at year end starts next year's supply.
Source: EPA, Guide to Air Cleaners in the Home, checked October 9, 2026; ENERGY STAR maintenance checklist, checked October 15, 2026.
Questions
How many air filters do I need for a year?
4 to 6 for each filter slot. The EPA says manufacturers typically recommend a change every 60 to 90 days, which works out to 4 changes a year at 90 days and 6 at 60 days.
Source: EPA, Guide to Air Cleaners in the Home, checked October 9, 2026.
How long does a 6-pack of furnace filters last?
For one slot, a year at a 60-day change, or about a year and a half at 90 days. With two slots of the same size, about half that.
Is every 90 days too long?
It is the long end of the EPA's 60 to 90 day range. Check the filter monthly, as ENERGY STAR suggests, and change it sooner if it looks dirty.
Source: EPA, Guide to Air Cleaners in the Home, checked October 9, 2026; ENERGY STAR maintenance checklist, checked October 15, 2026.
How do I know if my filter is dirty?
The American Lung Association suggests comparing it to a white sheet of paper. The EPA says if filters look heavily soiled when you change them, change them more often.
Source: American Lung Association, Air Cleaning, checked October 9, 2026; EPA, Guide to Air Cleaners in the Home, checked October 9, 2026.
Do I need a filter for every return vent?
Only the ones with a filter behind them. Some homes have one filter at the furnace, some have one behind each return grille, and some have both. Open each grille and count.
Source: Filterbuy, Where Is My HVAC Air Filter?, checked October 9, 2026.
Part of a system
This page is one part of a bigger job. The system page puts the parts in order.
SystemFurnace filter record: every slot, its size and the change datesFind every filter slot, write down its size and arrow, buy a year of spares, then check monthly and log each change on one printable record.8 steps · 4 parts · 1 page to printOpen the system
SystemMonthly house checkOne page for the monthly house check: test each smoke and CO alarm, look at the filter, read the water meter, check under the sinks, write one line.8 steps · 7 parts · 1 page to printOpen the system
SystemSummer cooling-season recordOne printable page for the cooling season: the AC model and age, the spring check-up, a filter date each month, hot rooms and bills to show the contractor.8 steps · 7 parts · 1 page to printOpen the system
The tool and more guides
Chapter 01HVAC filter size finder and replacement plannerTurn a nominal size like 16x25x1 into the filter's actual dimensions, or measure an old filter to find the size to buy, then plan the next change.Open the tool
ProblemNo size printed on my air filter: how to find itThe print on the frame is gone or the slot is empty. Measure the opening, round to the nearest inch, and know when you need a custom size.Read the guide
Practical noteWhat to change on move-in day: locks, garage opener and codesNew house, old keys. Here's the order to work in on move-in week: count what you got, change the locks, clear the garage opener, reset codes, then cut copies.Read the guide- Chapter 01All records toolsPrintable home records with a calculator behind each one: appliance and warranty log, HVAC filter sizes and change dates.Open the chapter
Sources
- Guide to Air Cleaners in the Home, U.S. Environmental Protection Agency. Checked October 9, 2026.
- Heating and Cooling Maintenance Checklist, ENERGY STAR (U.S. EPA and DOE). Checked October 15, 2026.
- Air Cleaning, American Lung Association. Checked October 9, 2026.
- Where Is My HVAC Air Filter? Return Vents, Air Handlers, and Furnace Locations, Filterbuy (US air filter manufacturer). Checked October 9, 2026.
- Air Filter Sizes: Nominal vs. Actual Dimensions, Filterbuy (US air filter manufacturer). Checked October 9, 2026.
Every outside number on this page names its source and the date we checked it. See them all on the sources page. Spotted an error? Tell us.