The air filter is the cheapest part of your HVAC system and the one most likely to cause an expensive problem. It is also the part homeowners get the most conflicting advice about.
Here is what the numbers mean, what thickness changes, and how to buy the right one.
Quick answer: A furnace filter MERV rating measures how well the filter captures airborne particles. Higher is not always better: the right furnace filter MERV rating is the highest one your system can move air through, and a thicker four-inch filter usually outperforms a dense one-inch filter.
MERV stands for Minimum Efficiency Reporting Value. It is a standardized scale from 1 to 16 for residential filters, measuring how effectively a filter captures particles in specific size ranges.
Higher numbers capture smaller particles. That part is simple. What is not simple is that higher is not automatically better.
MERV 1 to 4. Basic fiberglass. Protects the equipment from large debris, does very little for air quality.
MERV 5 to 8. Pleated. Catches dust, pollen, mold spores and pet dander. The practical default for most homes and comfortable for standard residential blowers.
MERV 9 to 12. Finer pleated media. Adds finer dust and some bacteria. Good for allergy households, provided the system can handle it.
MERV 13 to 16. Captures smoke and fine particulates. Effective, and demanding on airflow.
A filter works by restricting airflow. The finer the media, the more resistance it adds.
Residential blowers are designed for a specific total static pressure. Drop a MERV 13 one-inch filter into a system built around a MERV 8 and you can push pressure past what the blower was designed to handle. The result is reduced airflow, which overheats a furnace and trips its limit switch in winter, and causes an AC to freeze up in summer.
So the honest answer: the best MERV is the highest one your specific system can move air through without a pressure penalty. That is measured, not guessed, and any technician taking proper readings during a furnace tune-up can tell you where yours stands.
A four-inch filter has far more surface area than a one-inch filter of the same MERV rating. More area means the same filtration with less resistance per square inch, and much longer service life.
One-inch filters. Check monthly, replace when dirty. Most homes land between one and three months. Pets, kids and nearby construction shorten that. Our guide on how often to change your filter has the full schedule.
Four and five-inch media filters. Typically six months, which lines up neatly with spring and fall service visits.
If you are on a one-inch filter and tired of how often it needs changing, ask whether your system can accept a media cabinet. In many homes it is a straightforward upgrade, and it is also the right way to get serious filtration for fall allergies without strangling the blower.
The dimensions are printed on the cardboard frame of the filter currently installed. It reads something like 16x25x1.
Two things to know. The printed size is nominal, and the actual filter measures slightly smaller so it slides in — do not try to correct for it. And a filter that is too small lets air bypass around the edges, which defeats the entire point. It needs to fit the slot snugly.
You can order filters online through our store rather than guessing at the hardware store.
Every filter has an arrow printed on the frame. The arrow points in the direction of airflow, which means toward the furnace or air handler and away from the return duct.
Installed backwards, the media works against its design and loads up faster.
A clogged filter is not a minor issue. In rough order of how often we see it: reduced airflow driving temperature rise up, limit switch trips that look exactly like a furnace failure, frozen evaporator coils in cooling season, blower motor strain, higher energy use, and dust bypassing a loaded filter to coat the coil, which is a much bigger cleaning job.
A three-dollar filter causing a service call is a real thing and it happens constantly.
Check the filter on the first of every month. Hold it up to a light. If you cannot see light through the media, replace it. Write the date on the frame with a marker.
For four-inch media filters, tie it to your seasonal service visits — one at the fall furnace tune-up, one at the spring AC tune-up. Members of our maintenance plan get both, at $79 per tune-up, and membership is free to join.
J&J has serviced HVAC systems across Southwest Michigan for over 50 years.
No. A filter your system cannot move air through causes more problems than it solves. The right MERV is the highest one your equipment handles without a static pressure penalty.
The size is printed on the frame of the one currently in the slot. If the housing is empty, measure the opening and take the closest nominal size.
Only if it is specifically sold as washable. Standard pleated and fiberglass filters are disposable, and washing them damages the media and encourages mold growth.
Not sure which furnace filter MERV rating your system can handle? J&J can check it during your next visit.
Schedule service online or get in touch at (269) 965-1627 today! Prefer to pick a time yourself? Book your visit online.
9000 M-66 South • East Leroy, MI 49051
(269) 965-1627
Monday - Friday: 8:00am - 5:00pm
