Can a Higher-MERV Filter Hurt HVAC Airflow?

HVAC FILTERS • MERV RATINGS • INDOOR AIR QUALITY

You stand in the filter aisle.

MERV 8

MERV 11

MERV 13

Higher number must mean better.

So buy the biggest number, right?

Maybe.

HVAC FILTRATION HAS TWO JOBS

Capture particles

+

Maintain appropriate airflow

The best filter is the one that improves filtration and works properly with your HVAC system.

What Does MERV Mean?

MERV stands for:

MERV Minimum Efficiency Reporting Value

It is a rating system used to describe how effectively an air filter captures particles within specified size ranges.

In general, higher MERV ratings indicate greater particle-capture efficiency.

So Why Not Install the Highest MERV Possible?

Filters create resistance as air passes through them.

The HVAC blower needs to overcome that resistance.

FILTER Creates airflow resistance

→

BLOWER Has to move air through it

→

TOO RESTRICTIVE? Airflow can suffer

If a filter is too restrictive for the system, it can affect:

Heating performance

Cooling performance

Equipment temperatures

Comfort

Blower workload

Coil performance

BETTER FILTRATION IS ONLY BETTER IF THE SYSTEM CAN MOVE AIR Filtration and airflow need to work together.

MERV Rating Is Not the Only Factor

Two filters with the same MERV rating may not create identical pressure drop.

Design matters.

THIN FILTER Less media surface area

VS.

DEEPER MEDIA FILTER Potentially greater surface area

A thicker filter with greater surface area may sometimes provide strong filtration with less resistance than a thin filter trying to accomplish the same thing.

Simply comparing the MERV number on the package can be misleading.

Your Filter Cabinet Matters

Some homes have a basic 1-inch filter slot.

Others use:

1" Standard filter slot

4" Media filter

5" Deep media filter

IAQ Dedicated air cleaner

+ Larger filter cabinets

The available surface area changes how filtration can be designed.

IF INDOOR AIR QUALITY IS THE GOAL Improving the filter setup may make more sense than forcing a highly restrictive filter into a small slot.

What About Wildfire Smoke?

Fine smoke particles are exactly why homeowners become interested in better filtration.

EPA GUIDANCE EPA currently recommends MERV 13 or higher during smoke events where the HVAC system can accommodate it.

EPA also notes that an HVAC professional can help determine the highest-efficiency filter suitable for the system.

THE WORDS THAT MATTER “Can accommodate it.”

A higher-efficiency filter only helps if the HVAC system can continue moving the airflow it needs.

How Can You Tell if a Filter Is Too Restrictive?

Possible clues include:

Reduced airflow at registers

Unusual HVAC noise

Very rapid filter loading

Cooling performance changes

Low-airflow equipment problems

These symptoms can also have other causes.

MEASURE INSTEAD OF GUESS Airflow or static-pressure measurements can provide better information than assuming the filter is the problem.

Don't Forget to Replace It

A good filter becomes a bad airflow restriction if it is completely loaded with debris.

Replacement frequency depends on:

Filter type

System runtime

Pets

Smoke events

Household conditions

Construction dust

Other airborne particles

BETTER RULE Inspect it.

Do not rely entirely on the calendar.

Filtration Is a System Decision

If you want better indoor air quality, start with the question:

ASK THIS “What filtration can my HVAC system support effectively?”

not:

INSTEAD OF “What is the biggest MERV number at the hardware store?”

01 Filtration goal

02 Filter design

03 Cabinet size

04 System airflow

05 Maintenance

THE BEST FILTER ISN'T AUTOMATICALLY THE BIGGEST NUMBER It is the filtration setup that improves particle capture while allowing the HVAC system to operate properly.

WANT BETTER FILTRATION WITHOUT CHOKING YOUR HVAC SYSTEM?

Let's Match the Filter to the System

Air Comfort Heating & Air Conditioning helps homeowners throughout Anoka County, the North Metro and surrounding Minnesota communities improve HVAC filtration, understand MERV ratings and protect the airflow their heating and cooling equipment needs.

If indoor air quality is a priority, we can look at the filter, cabinet, airflow and system together instead of choosing based on one number on the package.

CALL 763-753-6623 REQUEST SERVICE

FREQUENTLY ASKED QUESTIONS

MERV & HVAC Filter Questions

Is MERV 13 good for wildfire smoke?

EPA currently recommends MERV 13 or higher where the HVAC system can accommodate the filter.

Can a high-MERV filter damage my HVAC system?

Excessive airflow restriction can create HVAC performance problems. Filter selection should account for the airflow requirements of the system.

Is a thicker filter better than a 1-inch filter?

Larger media filters can provide more filter surface area and may offer different airflow characteristics, but the correct setup depends on the HVAC system and filter cabinet.