The air filters in your furnace have an important job to do. They remove dust and countless other particles from the air that passes through your HVAC, which not only protects your furnace from potentially damaging buildup, but helps improve your air quality and keeps you and your family healthy.
Furnace filters can remove dust, dirt, pollen, mold spores, insect waste, pet dander, dust mites and many other particles from the air, but not all filters are created equal. MERV ratings, which are usually printed on filters’ packaging, offer a simple and effective way to compare different filters and choose the ones that are best for your household.
MERV stands for “Minimum Efficiency Reporting Value,” and it essentially indicates how effectively a furnace traps particles from the air. All filters are assigned a rating between 1 and 20, and a higher rating means that a filter can catch smaller particles.
Choosing the best filter can be a bit of a balancing act, because low-rated filters lat a lot of particles pass right through, but a filter that is too efficient can become clogged quickly and cause air flow issues in your HVAC. It’s a good idea to know what specific MERV ratings mean in terms of efficiency.
MERV 1 to 4 – Filters at the low end of the MERV scale can only catch particles larger than 10 microns in diameter, which includes hair, larger dust particles and textile fibers. These filters do protect your furnace somewhat, but they do very little to improve your indoor air quality.
MERV 5 to 8 – These filters are a little better, and can catch particles 3 microns and larger. A filter rated between 5 and 8 is sufficient in many homes, but if anyone in your household suffers from allergies, you may want to consider a higher-rated filter.
MERV 9 to 13 – A rating in this range means that a filter can trap particles as small as 1 micron, which includes mold spores, humidifier dust and even some types of bacteria. These filters offer a good balance of cost and efficiency, and are more or less ideal for most HVAC systems.
MERV 14 to 16 – These filters are highly efficient, able to catch bacteria, most tobacco smoke and all particles larger than 0.3 microns in diameter. The downside to filters this efficient is that they get dirty quickly, which means they need to be changed or cleaned often, and they may restrict air flow in many systems.
- MERV 17 to 20 – A filter rated 17 or higher can catch particles as small as 0.1 microns, which includes just about everything. Unfortunately, filters that are this efficient make it extremely difficult for air to pass through your HVAC, which can cause overheating and short-cycling. These filters are almost never used in residential heating and cooling systems.