SWITCHING TO A HIGHER MERV RATED FILTER? PUMP THE BREAKS

During Covid we saw a big push for better filtration of facility air. Some facilities switched to tighter, higher MERV, filters without understanding the ramifications this would have on their HVAC equipment. Today we are going to cover what happens to your HVAC equipment when switching to a higher MERV rated filter. We are also going to you how you can improve your filters without damaging your equipment.

EFFECTS OF HIGHER MERV RATED FILTERS ON HVAC SYSTEMS

It’s important to understand that sliding in a tighter filter and walking away isn’t the right fix. Blower motors are designed to meet a certain static load and can’t always overcome a tighter filters restrictions on air flow.

If you were to throw in a high MERV filter, without adjusting anything else, you’ll increase the pressure drop across the unit. This is because, without changes, the motor can’t overcome the tighter filter. This reduces the airflow through the unit, causing a cascade of problems.

If we have lower airflow across your heat exchanger, that we are blasting a hot flame into, the heat exchanger temperature begins to rise. This means our heat exchanger is running hot and you will eventually burn holes in the heat exchanger. Additionally, your motor will also begin to heat up as there is less airflow and it struggles to keep up.

“85% motors that get sent back to Johnstone Supply are from a winding failure from getting to hot. This is caused from restrictions in airflow.” – Jason Carlson – VP of Training, Johnstone Supply

On top of this, your HVAC unit now has to stay on longer to deliver the same amount of air. This decreases the units efficiency. So what can you do?

SOLUTIONS FOR IMPROVED AIRFLOW

If you want to use a tighter filter, there are three primary solutions to maintain proper airflow:

1. Rebalancing equipment after adding a higher MERV rated filter
2. Adjust Motor Speed: Have a balancing company adjust the sheaves or pulleys on the motor to increase fan speed. If the existing motor’s horsepower is sufficient, this can overcome the pressure drop caused by a tighter filter.
3. Install a New Motor: If the current motor’s horsepower is insufficient, you need to install a new motor.

Note: Failing to rebalance your equipment after changing to a tighter filter means you’re knowingly restricting airflow. Over time you will cook the heat exchanger or the motor if adjustments aren’t made.

THE ROLE OF ECM MOTORS

Electronically Commutated Motors (ECMs) are now common in modern HVAC equipment. These motors are controlled by a control panel that adjusts fan speed to compensate for loss in airflow. They contain a module that measures static pressure and adjusts speed based on demand. While this can protect the heat exchanger if filters get plugged up, ECM motors become extremely inefficient at higher ranges. They also often can’t handle the increased restriction caused by tighter filters.

Newer units equipped with ECM motors may ramp the motor down to half speed if they detect a static pressure over 0.8. This protects the motor from overheating but also means the unit won’t run unless you make modifications to your system.

UNDERSTANDING MERV RATINGS

The Minimum Efficiency Reporting Value (MERV) tells us how tight a filter is or how small the particles it can capture. MERV ratings range from 1 to 20.

As the rating increases, the minimum size of the particles filtered out gets smaller, meaning more particles are captured. Here is a breakdown of MERV ratings and the particles they filter:

• MERV 1–4: > 10.0 μm (pollen, dust mites, textile fibers)
• MERV 5–8: 10.0–3.0 μm (mold spores, pet dander)
• MERV 9–12: 3.0–1.0 μm (legionella, lead dust)
• MERV 13–16: 1.0–0.3 μm (bacteria, smoke)
• MERV 17–20: < 0.3 μm (viruses, carbon dust)

While higher MERV ratings are effective at capturing smaller particles, they also create more resistance. This can lead to reduced airflow and potential damage to your HVAC system. For instance, MERV 8 filters catch larger particles and are less restrictive, while MERV 11 filters catch smaller particles and are more restrictive. This means?MERV 11 filters not only have higher initial resistance but also build up additional resistance faster as they capture more debris.

FILTER COMPARISON: MERV 8 VS. MERV 11

• MERV 8: Less restrictive, allows for better airflow, holds up to the light and you can see through it.
• MERV 11: More restrictive, captures smaller particles, builds up debris faster, and increases pressure drop.

MAINTENANCE TIPS WHEN SWITCHING TO A HIGHER MERV RATED FILTER

When switching to a higher MERV rated filter, it’s crucial to follow some maintenance tips to ensure your HVAC system runs efficiently:

1. Regular Inspections: Check your filters regularly. Higher MERV filters can become clogged faster, so more frequent inspections are necessary. This ensures that you catch any blockages early and maintain optimal airflow. Ignoring this step can lead to significant performance issues and increased wear and tear on your system.
2. Scheduled Replacements: Replace filters according to the manufacturer’s recommendations or even more frequently if the filters appear dirty. Higher MERV rated filters capture more particles, which means they can become saturated more quickly. Timely replacements prevent excessive strain on your HVAC system.
3. Monitor System Performance: Keep an eye on your HVAC system’s performance. If you notice a drop in efficiency or an increase in running time, it might be due to the higher resistance of the filter. Monitoring performance helps in identifying issues early, ensuring that your system remains effective and energy-efficient.
4. Professional Maintenance: Schedule regular maintenance with a professional HVAC technician to ensure your system is properly balanced and running efficiently. Professionals can adjust system settings and make necessary modifications to accommodate the higher MERV rated filters, ensuring long-term reliability.

COST IMPLICATIONS OF HIGHER MERV RATED FILTERS

While the initial cost of the filter might be higher, there can be additional costs associated with maintaining proper airflow and system efficiency. This might include:

1. Higher Energy Bills: Due to the increased resistance, your HVAC system might have to work harder. This leads to higher energy consumption and increased utility bills. This extra effort translates to more energy usage, which can quickly add up, impacting your monthly budget.
2. Maintenance Costs: More frequent filter replacements and potential adjustments to the HVAC system can lead to higher maintenance costs. Ensuring optimal performance with higher MERV rated filters might require additional services from HVAC professionals, increasing overall maintenance expenses.
3. System Wear and Tear: The increased strain on the system can lead to more frequent repairs. It can also lead to a shorter lifespan for your HVAC equipment. Components like motors and heat exchangers can suffer from the added stress, necessitating more frequent repairs or replacements, thereby increasing long-term costs.

FREQUENTLY ASKED QUESTIONS

Q: DO HIGHER MERV FILTERS RESTRICT AIRFLOW?

Yes, higher MERV filters are more restrictive and reduce airflow. If you make adjustments to the HVAC system it can eventually handle the increased resistance.

Q: CAN HIGHER MERV FILTERS DAMAGE MY HVAC SYSTEM?

If not properly managed, high MERV filters can cause increased pressure drop, leading to overheating and potential damage to the heat exchanger and motor.

Q: HOW CAN I IMPROVE FILTRATION WITHOUT DAMAGING MY HVAC SYSTEM?

Solutions include increasing the filter area, adjusting motor speed, or installing a new motor with higher horsepower.

NEED HELP SWITCHING TO A HIGHER MERV RATED FILTER?

Reach out to us via email at [email protected] or give us a call at 800-237-3154.