High MERV rating Air Filters on older HVAC system, bad?

I have an HVAC system that is older (analog thermostat) but seems to work fine; someone in HVAC warned me that using too high a “MERV” rating would be bad for it, because the motor would blow out, and that I should use only the fiberglass ones; another HVAC guy said that that was unnecessary but didn’t give any detail. So I have been using Filtrete 1000 (about Merv 11?) for years, replacing timely.

So are higher MERV ratings, like the premium filters (Merv 13?) from 3m, bad for any HVAC system that isn’t newer? Or is it better for it to have the filtering keep it from dust?

Well I have a limited knowledge on this, but I do have a rather thick HVAC textbook in front of me so ill paraphrase what it says.

By having too high of a MERV rating you could be overworking the blower. The only real way to tell if its too high is to measure the pressure drop across the filter. I doubt you have a manometer laying around to check.

For residential use though, unless you or someone in the house has real sensitive allergies or asthma or anything in that vein, a MERV 8 is completely fine and still provides excellent filtration. For just dust you start filtering it out around MERV 4/5. MERV 8 is getting out dust, lead dust, pollen, mold spores, which you can get out at a MERV 5/6, but its just getting more of them so to say. MERV 13 your starting to completely filter out bacteria, tobacco smoke, and other incredibly small particles. MERV 13 and above are generally used in hospitals and such.

In my very amateur opinion, your probably already using too much filter, especially if you said you have an older system, and reducing the life span on your blower.

You say that you would be overworking the blower, and I’ve always thought that to be true, but thinking about it, I don’t think it’s true. If there is not enough air for the blower to pull through the filter, then how does that put more strain on the blower? It would be like operating it in a vacuum, right? The only strain would be from the system having to be on for longer periods because not enough air would be moving across the coils to operate most efficiently.
Sent from my iPhone using Tapatalk

Well I haven’t quite finished school yet, so I may be wrong on some of this.

Any HVAC system needs the right amount air flow across the coil or heat exchanger to operate properly. When you over-filter or have a clogged filter, this increases the pressure drop across the filter, it reduces the airflow. In order to maintain the proper airflow, the blower works harder and harder to pull the amount of air needed. This is harder on the motor, and it could overheat the motor. Running with too little airflow could potentially cause other problems as well with the compressor and overheating of the heat exchanger causing it to shut-off. You could also get icing on your coils in AC mode, and when heating reduces the efficient of the system, making it run longer and cost more so your paying more for the same amount of heat.

I have been using the same filters for as long as they have made them. I currently use the Filtrete with allergen removal and just below the high end odor removal version. Looking at the website I think it is the same as you use. No problems on my system.