We all know the higher vs lower MERV filter deal: With higher MERV filters (MERV 11, 14), you get better filtration but higher resistance (more strain on AC, furnace). That’s because higher MERV filters have a higher pressure drop across the filter. What are pressure drops over different MERV filters, and how do MERV 6 vs. 8 vs. 11 vs. 14 filter pressure drops compare?
We are going to look at a rough MERV filter pressure drop chart to see the differences (focusing on MERV 8, MERV 11, and MERV 14 filters, since we use these ones in air conditioners and furnaces the most). This is vital to understand when we should pick MERV 8 vs 11 vs 14 for your HVAC appliance.
Here is the key point:
Since higher MERV filters are made out of more densely packed fibers, it is harder for AC or furnace to deliver adequate airflow. This is because of higher pressure drops of MERV 11 and MERV 14 filters, for example, that an AC or a furnace has to work against.
Specific filter pressure drops depend on filter type, filter thickness, airflow (CFMs), and even manufacturers (MERV 8 filtrate filter, for example, can have a different pressure drop than the 3M MERV 8 filter). Here is the standard MERV filter pressure drop table:
MERV Pressure Drop Table And Chart
| Filter MERV Rating | Pressure Drop (300 CFM) | Pressure Drop (500 CFM) | Pressure Drop (10,00 CFM) |
|---|---|---|---|
| MERV 6 | 0.10 in. w.g. | 0.15 in. w.g. | 0.25 in. w.g. |
| MERV 7 | 0.12 in. w.g. | 0.18 in. w.g. | 0.30 in. w.g. |
| MERV 8 | 0.14 in. w.g. | 0.20 in. w.g. | 0.35 in. w.g. |
| MERV 9 | 0.16 in. w.g. | 0.22 in. w.g. | 0.40 in. w.g. |
| MERV 10 | 0.18 in. w.g. | 0.25 in. w.g. | 0.45 in. w.g. |
| MERV 11 | 0.20 in. w.g. | 0.28 in. w.g. | 0.50 in. w.g. |
| MERV 12 | 0.22 in. w.g. | 0.30 in. w.g. | 0.55 in. w.g. |
| MERV 13 | 0.24 in. w.g. | 0.33 in. w.g. | 0.70 in. w.g. |
| MERV 14 | 0.26 in. w.g. | 0.36 in. w.g. | 0.90 in. w.g. |
Note: We measure filter pressure drop in units called ‘inches of water column’, abbreviated as ‘in. w.g.’ in the table.
From this table, we can see that:
- Pressure drop at 300 CFM ranges from 0.10 (MERV 6) to 0.26 (MERV 14) in. w.g.
- Pressure drop at 500 CFM ranges from 0.15 (MERV 6) to 0.36 (MERV 14) in. w.g.
- Pressure drop at 1,000 CFM ranges from 0.25 (MERV 6) to 0.90 (MERV 14) in. w.g.
We see that MERV 14 presents about double the resistance of the MERV 8 filter at lower (300 CFM) and standard (500 CFM) airflow. At higher airflow (1000 CFM), the MERV 14 presents triple the resistance compared to the MERV 8 filter (0.90 vs. 0.35 inches of water column pressure, respectively).
To better visualize the difference in pressure drop between these MERV filters, we prepared the following chart:
MERV 8 vs MERV 11 vs MERV 14 Pressure Drop Chart
From this graph, we see that MERV 14 filter is the most resistive (compared to MERV 11 and MERV 8 filters). By looking at 300 CFM, 500 CFM, and 1000 CFM airflow, we see 2 very important characteristics:
- At lower airflow (300 CFM, 500 CFM), the pressure drop across the MERV 8, 11, and 14 filters is significant but constant.
- At higher airflow (1000 CFM), the pressure drop across finer filters like MERV 14 increases dramatically when compared to less finer filters like MERV 11 and MERV 8.
Let’s explain how understanding this chart is useful when choosing the right MERV filter:
What To Consider When Choosing MERV Filter (Key Takeaway)
We get questions from people in our comments about which MERV filter they should choose for their AC, heat pump, furnace, etc. Obviously, homeowners are rightfully concerned that a higher MERV filter – more strain on the HVAC unit – will reduce the lifespan of said unit.
On the other hand, if you have a higher MERV filter, like MERV 14, you will get better filtration and thus cleaner air to breathe.
The main run-of-the-mill advice of sticking to the MERV filter that manufacturers of the HVAC unit specify always holds true. However, many specs may read something along these lines: “Allowed Filters: MERV 8, MERV 11, MERV 14”. When faced with this choice, you can use this simple rule of thumb:
- If you run your HVAC unit at lower airflow (mostly 500 CFM or below), you can opt for higher MERV filters like MERV 14. MERV 11 is still the best compromise between filtration and strain on the AC unit. You can use higher MERV filters for smaller and standard-sized air handlers. Example: 1 ton or a 9,000 BTU/hr air handler will produce about 400 CFM of airflow. You can slip in the MERV 14 in that, since the airflow is fairly low.
- If you run your HVAC unit at higher airflow (say 1000 CFM), you should opt for lower MERV filters like MERV 8, maybe MERV 11. This is because – as we see in the pressure drop chart above – the pressure drop and, thus, strain on the HVAC unit is much higher at higher airflow if we use a restrictive MERV 14 filter. Example: 2 ton or an 18,000 BTU/hr air handler will produce about 800 CFM of airflow. You can’t use MERV 14 here; MERV 8 or even possibly MERV 11 are clearly much better choices (won’t put your AC or furnace under too much pressure, prolonging its lifespan).
So, in essence:
- Low airflow = Higher MERV filter is OK.
- High airflow = Higher MERV filter is not OK. You should usually go with MERV 8.
We hope these filter pressure drop data-point give you a good insight into how MERV 8, 11, and 14 pressure drops differ. Based on these differences, you can make a more informed choice of the filter that will not reduce the lifespan of expensive HVAC units and still produce as clean air as the HVAC unit allows.