Are MERV 8 — 13 Filters Too Restrictive for Central AC or Furnaces? Not if You Manage Air Velocity!
Are you wondering whether a MERV 8, MERV 11, or MERV 13 air filter might be too restrictive for your home’s air conditioner or furnace?
As an world known air filtration expert, I can assure you that the simple answer is no — these filters are not too resistrictive if installed correctly. In fact, when properly installed, MERV 13 air filters offer better protection for your AC and furnace by capturing finer particles that could otherwise build up in your system.
The real key is understanding how air velocity impacts filter performance, a factor we refer to in the industry as ‘resistance to airflow.’
Here we explore what makes MERV ratings crucial, why air velocity matters so much, and how to get the most out of your HVAC system with higher-rated filters. It’s also worth noting that many common furnace repair and AC repair issues can be traced back to a poor balance between air filters and air velocity.
What Is MERV?
Before discussing installation, it’s important to understand what MERV actually is.
MERV, or Minimum Efficiency Reporting Value, is a rating system developed by the ASHRAE (American Society of Heating, Refrigeration, and Air-Conditioning Engineers). To be more specific by Technical Committee TC 2.4 and SSPC 52.2. MERV ratings measure how effectively a filter captures airborne particles of various sizes. The higher the MERV rating, the better the filter is at capturing smaller particles. Many people assume that higher MERV ratings inevitably create more resistance to airflow (or “restriction”). While this perception is accurate, there are effective ways to reduce airflow resistance, particularly by lowering the air velocity through the filter.
While some stores display different rating systems, such as FPR (Filter Performance Rating) or MPR (Microparticle Performance Rating), these are just marketing labels developed by manufacturers and not nationally recognized standards or peer reviewed.
Common Misconception: Higher MERV Equals Restricted Airflow
One common misconception is that higher MERV 13 filters restrict airflow too much, causing strain on central AC systems or furnaces. But the truth is, higher MERV filters is beneficial for your indoor air quality, as they trap smaller, harmful particles — like pollen, mold spores, and fine dust — that lower-rated filters would miss.
The Real Factor: Air Velocity
So if MERV 13 filters aren’t the problem, what is? The real issue lies in air velocity. High air velocity can make any filter, regardless of its rating, appear overly restrictive. When air moves too quickly through a filter media (fabric), it creates more resistance, limiting airflow and making your system work harder.
The solution is to lower the air velocity through the filter, which is often achieved by increasing the filter media surface area, allowing air to pass through more smoothly. For example, this article on “what causes an air conditioner to freeze up” suggests doubling the return duct surface area to reduce air velocity while maintaining airflow intact — an effective approach that helps prevent system strain.
If the width and height of the air filter track are fixed and not modifiable, Another solution is to retrofit, a 1" deep filter with 4" deep. This trick has been used in the industry for many years usually known as depth filter.
How to Use MERV 13 Filters Without Overloading Your System
To use higher-rated MERV filters without compromising your HVAC system, here are some strategies to ensure balanced air velocity:
- Increase Filter Surface Area: Consider using a filter with a larger surface area, which reduces air velocity and allows air to flow more easily.
- Check Your Fan Speed: Many HVAC systems allow for fan speed adjustments. Slowing down the fan reduces air velocity, which can lessen airflow resistance.
- Invest in a Variable Speed Blower Motor: If you’re committed to higher filtration, upgrading to a variable speed motor can help. These motors adjust the fan speed to control air velocity automatically, balancing airflow and improving efficiency.
- Replace Filters Regularly: Even a high-quality filter becomes restrictive if it’s clogged with dust and particles. Regular replacement keeps the air velocity and airflow resistance under control.
Why a Higher MERV Rating Can Be a Smart Choice
If you’re looking to improve indoor air quality — especially if you have allergies or respiratory sensitivities — using a MERV 13 filter can be a worthwhile decision. These filters capture smaller particles that can otherwise circulate in your home, including bacteria, allergens, and even some viruses.
The benefits of MERV8, MERV 11 or MERV 13 filters, when used correctly, far outweigh the risks of airflow issues, especially if you understand how to manage air velocity.
Final Thoughts
Choosing the right filter for your HVAC system isn’t just about picking a MERV rating and calling it a day. It’s about understanding the balance between airflow, air velocity, and filtration needs. MERV 11 and MERV 13 filters can absolutely improve your indoor air quality without causing system strain, as long as you control air velocity. By implementing simple adjustments to your fan speed or considering filters with larger surface areas, you can safely enjoy the benefits of cleaner air in your home.
So next time you’re in the market for a filter, don’t shy away from higher MERV ratings. With a little knowledge and a few adjustments, you can achieve optimal indoor air quality without compromising your HVAC system’s efficiency.
