How Often Should You Change a MERV 13 Furnace Filter?
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Both Filtrete filters in our catalog state a three-month replacement interval. That is a reasonable default, but a higher-MERV filter in a house with pets, construction dust or heavy runtime loads faster than one in an empty apartment. Check it monthly for the first cycle, replace when it is visibly loaded rather than on the calendar, and remember the EPA's point that a dirty or overloaded filter does not work well.
The two Filtrete filters we list state three months. Treat that as a starting point rather than a schedule: look at the filter after the first month, and replace it when it is visibly loaded. A filter's life is set by how much air has gone through it and how dirty that air was, neither of which the manufacturer can know.
We do not hold a stated interval for the Aerostar filter in our catalog.
Filter intervals are one of the few pieces of home maintenance where the interval printed on the box and the right interval for your house can diverge substantially in either direction, and where checking takes less time than reading about checking.
What the filters we list actually say
| Product | MERV | Stated interval (months) | Pack count | Nominal size | Link |
|---|---|---|---|---|---|
| Filtrete Filtrete 20x25x1 Air Filter, MERV 13, MPR 1900 | 13 | 3 | 2 | 20x25x1 | Check price |
| Filtrete Filtrete 12x24x1 Air Filter, MERV 11, MPR 1000 | 11 | 3 | 4 | 12x24x1 | Check price |
| Aerostar Aerostar 20x25x1 Air Filter, MERV 13 | 13 | — | 6 | 20x25x1 | Check price |
Multiply those two columns together and you get the more useful number, which is how long a pack lasts at the stated interval:
- Filtrete 20x25x1 MERV 13 — three months, two per pack, so about six months per pack.
- Filtrete 12x24x1 MERV 11 — three months, four per pack, so about twelve months per pack.
- Aerostar 20x25x1 MERV 13 — six per pack. At a three-month interval that would be about eighteen months, though the interval for this filter is not one we hold.
What actually determines the interval
Four variables, none of which appear on the packaging.
System runtime
The filter only loads while air is moving through it, so a system running through a hot summer loads its filter far faster than one idle in a mild autumn.
What to look for: Whether your fan runs continuously or only with heating and cooling. Continuous-fan settings shorten filter life considerably.
Pets and occupancy
Dander and hair add to what the filter has to hold, on top of ordinary household dust.
What to look for: Visible fur on the filter face at the first monthly check, which is a reliable sign you are on a shorter cycle than the box assumes.
Dust events
Renovation, sanding or nearby construction can load a filter in days rather than months.
What to look for: Any work that produces airborne dust. Change the filter after the work finishes rather than waiting out the interval.
MERV rating
A filter capturing more particles accumulates more material, all else equal.
What to look for: The EPA's guidance is at least MERV 13, or as high as the system will accommodate. Higher capture is worth having; it just needs looking at more often.
Why an overdue filter is a system problem too
The air-quality argument is the obvious one, and the EPA states it directly: a dirty or overloaded filter does not work well. The mechanical argument gets less attention and costs more. A loaded filter is a restriction, and a one-inch filter has little depth to spare before that restriction bites. Restriction reduces airflow across the system, and reduced airflow in cooling is the classic route to a frozen evaporator coil and a call-out.
This is also why upgrading MERV and forgetting the filter is a bad combination: you have raised the baseline restriction and then allowed it to climb. The fix is not a lower MERV. It is looking at the filter.
Best for staying ahead of the interval
Aerostar Aerostar 20x25x1 Air Filter, MERV 13
Six MERV 13 filters in the pack, which makes it far more likely a spare is in the house on the day you notice the current one is loaded.
- Merv Rating
- 13
- Pack Count
- 6
- Nominal Size
- 20x25x1
- Pleated
- true
MERV 13 with a stated interval
Filtrete Filtrete 20x25x1 Air Filter, MERV 13, MPR 1900
Publishes a three-month replacement interval, which is a useful starting default. Two per pack, so plan on reordering roughly twice a year.
- Merv Rating
- 13
- Replace Months
- 3
- Pack Count
- 2
- Mpr
- 1900
We do not hold a manufacturer replacement interval for the Aerostar filter, and we hold no pressure-drop or airflow-restriction figures for any of the three filters in our catalog. Loading rate is also entirely house-specific, so no interval on this page should be treated as a prediction for your system.
If you are weighing a MERV upgrade at the same time as a schedule change, the airflow trade-off is the thing to understand first: MERV 13 versus MERV 11 in a one-inch filter.
The short version
- Three months is the stated interval on both Filtrete filters we list.
- Load depends on runtime, occupancy, pets and dust, none of which the box knows about.
- A loaded filter restricts airflow, which is a system problem as well as an air-quality one.
- Buy in pack sizes that match your real interval, not the one on the label.
Sources
- Dehumidifiers — ENERGY STAR
That dehumidifier capacity is measured in pints per 24 hours, and that the capacity needed depends on the size of the space and the conditions in it.
- Energy Conservation Program: Test Procedure for Dehumidifiers — US Department of Energy (Federal Register)
That a dehumidifier's capacity is defined by federal test procedure as the volume of water in pints removed from ambient air per day, normalized to a standard ambient temperature and relative humidity.
- A Brief Guide to Mold, Moisture and Your Home — US Environmental Protection Agency
That indoor humidity should be kept below 60 percent, ideally between 30 and 50 percent relative humidity.
- Guide to Air Cleaners in the Home — US Environmental Protection Agency
That a portable air cleaner should have a clean air delivery rate (CADR) large enough for the size of the room, that a higher CADR filters more particles and serves a larger area, and that most portable air cleaners carry a CADR rating on an AHAM label.
- Guide to Air Cleaners in the Home (room sizing) — US Environmental Protection Agency
That the room area should be compared against the maximum recommended room size on the packaging; that an open floor plan means considering the entire space the cleaner would serve; and that ceilings above 8 feet mean sizing up.
- Guide to Air Cleaners in the Home (furnace filters) — US Environmental Protection Agency
That a furnace or HVAC filter should be rated at least MERV 13, or as high as the system will accommodate, and that a dirty or overloaded filter does not work well.
- Air Changes per Hour FAQ — AHAM Verifide
That the AHAM Verifide seal gives a suggested room size based on 4.8 air changes per hour, alongside reduction rates for tobacco smoke, dust and pollen known as clean air delivery rates (CADR), and that certified units are independently tested by a third-party laboratory.
- Air Filtration Standards — AHAM Verifide
That AHAM's standard for measuring an air cleaner's efficacy is the Clean Air Delivery Rate (CADR), which indicates the volume of filtered air delivered with separate scores for tobacco smoke, pollen and dust, and that a higher CADR means faster filtering.