05 Feb

How to Select The Right MERV Rating for Your Furnace Filter


 How to select the right MERV rating for your furnace filterSince it’s still winter, here’s a quick PSA – when was the last time you replaced your furnace filter? Most disposable filters should be replaced every three months.

Now that we have that covered, let’s talk about how to select the right air filter for your furnace. One important aspect to look at is the filter’s MERV rating.

What does MERV mean?

MERV stands for Minimum Efficiency Reporting Value, which is a rating system designed by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). The rating indicates the size of particles the air filter is designed to capture. Ranging from 1 to 20, the larger the number, the better the filter is at catching small particles.

Below is a table grouping MERV ratings by particle size:

MERV Min. particle size Typical controlled contaminant Typical Application 
1–4 > 10.0 μm Pollen, dust mites, cockroach debris, sanding dust, spray paint dust, textile fibers, carpet fibers Residential window AC units
5–8 10.0–3.0 μm Mold, spores, dust mite debris, cat and dog dander, hair spray, fabric protector, dusting aids, pudding mix Better residential, general commercial, industrial workspaces
9–12 3.0–1.0 μm Legionella, Humidifier dust, Lead dust, Milled flour, Auto emission particulates, Nebulizer droplets Superior residential, better commercial, hospital laboratories
13–16 1.0–0.3 μm Bacteria, droplet nuclei (sneeze), cooking oil, most smoke, and insecticide dust, most face powder, most paint pigments hospital & general surgery
17–20 < 0.3 μm Virus, carbon dust, sea salt, smoke Electronics & pharmaceutical manufacturing cleanroom

Note: Table copied from Wikipedia

What MERV Should I Use in My Home Furnace?

In general, filters with higher MERV ratings are more effective and improve air quality – but are also more expensive. Plus, higher doesn’t always mean better for homeowners. MERV ratings above 16 are typically used in specialized commercial settings where air filtration is critical, such as hospitals.

For residential furnaces, filters range from 4 to 12 on the MERV scale. A basic MERV 4 filter will likely be the cheapest but won’t catch certain small particles (like dust mites and pet dander) that could be in your home. If your family has health or allergy issues, then you may want to look for a high-efficiency filter that’s MERV 11 or higher. But for most households, a MERV 7 or 8 filter might be the sweet spot between performance and cost.

Other Rating Systems.

When shopping for furnace air filters, don’t confuse MERV with other rating systems that may appear on packaging (especially from big box home improvement stores). This isn’t to say one system is right and the other is wrong – they’re just rated by different standards.

A word of caution.

One final note. Since higher-rate filters allow less air to flow through your furnace, it’s a good idea to check if your system has a maximum MERV rating. The wrong type of air filter can force your furnace to work harder and increase the risk of it breaking down.

If you have any questions about picking the right air filter for your home furnace, give Robert B. Payne, Inc. a call, and we’ll be happy to provide our expert opinion.