Filtration vs Static Pressure - Which is More Important?

Hogan

In another thread here I have discussed my findings of static pressure in my two furnace systems.   Both seem constrained by return airflow, not supply airflow.   Pressure above the AC coil in each is only 0.06.    It's the return pressure before and after the filter that is high.  

The question I have is, is it better to still run my Merv 7 1 inch pleated filters to get better filtration for the equipment even though it results in a return air pressure of like .62 vs .46 if I use a cheap Merv 2 fiberglass filter?    I know it's harder on the blower but I also had read something that newer blower motors with ECM can just torque up more to maintain flow and so they will maintain the CFM you need, and thus you might as well get the better filtration?     What do you think

STEVEusaPA

I think most people think these filters actually filter the air. Their main job in this typical application is to protect the blower motor.
Higher static pressure will reduce blower motor life.
Ecm motors are much more expensive than standard psc motors.

EBEBRATT-Ed

I think your after the wrong thing. Everyone seems pretty sure that the returns are undersized. I know you have said many times you don't wat to rip things apart to increase the duct size. Many have given you other suggestions.

Taking static pressure reading is not going to make the return ducts enlarge. Somebody either you or a sheet metal guy needs to figure out what you need, how to increase the supply and return ducts so you get the air flow the furnace needs.

Hogan

EBEBRATT-Ed said:

I think your after the wrong thing. Everyone seems pretty sure that the returns are undersized. I know you have said many times you don't wat to rip things apart to increase the duct size. Many have given you other suggestions. Taking static pressure reading is not going to make the return ducts enlarge. Somebody either you or a sheet metal guy needs to figure out what you need, how to increase the supply and return ducts so you get the air flow the furnace needs.

I fully understand my return ducts are undersized.   My decision point is how to make the best of it vs some huge expensive job of ripping open walls or ceilings.    So the question about the filter is just one small refinement on the current making the best of it spectrum, and so my question is, is it better to let the blower run under a lower static pressure while not having as strong of a filtration effect, or is it more important to filter dust from going thru the blower and heat exchanger and AC coil.   My guess is that it is actually better to have the motor run on the lower pressure so using a fiberglass filter is better here for the time being.  

Yes I would love to improve the return flow but looking at the house currently it's not a simple solution.  I've been looking for space where I could have a floor vent cut in and there isn't a logical spot that lines up with the return trunk.   I can't just drop a hole right in the middle of the kitchen floor of course.   One thing I'm looking at is the kitchen island.  There is currently a supply vent on one bottom corner of the kitchen island that is one of the strongest heat flow vents because it is so close to the furnace below it.   I am wondering if we could make a return vent on the other side of that island that could tie into the return ducts.  Unfortunately it seems all of the joist spaces in the open furnace room underneath are already occupied by something that would get in the way, whether an existing supply or return duct or a bathroom vent fan duct or a laundry room dryer duct etc