When you shop for a filter for your furnace, you may wonder what the difference is between lower-cost and higher-end filters. Generally speaking, the denser the filter, the better job it does of keeping dirt and other particles out of your equipment. So what’s the right filter for your furnace? Read on for some information that will help you choose.

MERV Rating

HVAC system filters are rated by the MERV, or minimum efficiency reporting value, system. Manufacturers sometimes use their own rating systems, but MERV is the industry standard.

Homeowners who choose the cheapest fiberglass filters, usually rated MERV 1-4, are providing minimal protection for their HVAC systems from the largest dirt and debris particles. Nor do these filters do much to improve indoor air quality.

Higher-rated filters keep smaller particles out of the HVAC system. They also capture more allergens and other particles that might be recirculated into the home’s air, causing respiratory problems. Better quality filters for the home are usually pleated, providing greater surface area to trap particles, and are made of a cotton and polyester blend. They generally last longer than cheaper filters; depending on how dusty the home is, they may be used for as long as three months before changing the air filter is necessary.

Filters rated MERV 5-7 do an adequate job of keeping most airborne particles out of the HVAC system and the home’s air, including mold, dust, pollen and textile and carpet fibers. Filters rated between MERV 8 and 12 are recommended for the typical home, while filters rated MERV 13-20 are too dense for most residential HVAC systems, and cannot be used without significant modifications to accommodate airflow.