Originally posted by jclancy
When you say add a new return run off the return drop, I apologize, but I don't know what you mean....going from where to where?
From the new properly sized return drop to the space that the unit is heating. Preferably to a location that doesn’t already have a return (but returns can’t be pulled from garages, bathrooms, kitchens, or utility rooms).

I guess my question is....if my existing ductwork can only handle X amount of air flowing through them because they're small, what is the benefit to the furnace of having more air supplied to it via a larger return?
Please see my previous post. I attached it below.

Is it solely to prevent the temperature rise that was mentioned?
Please see my previous post. I attached it below.

How will it do that if the air doesn't have anywhere to go?
The air enters the furnace from the return and then exits the furnace through the supply. If either of these is inadequate, they need to be addressed. The only way to know is to do some test to your equipment (temp rise, static pressure, gas pressure, etc…)

But with the existing ducts, does it make sense?
If your equipment is not operating with-in manufactures specifications, YES it makes all the sense in the world to redo the ducting so your furnace will last!

Original post follows below:

Originally posted by jultzya
Originally posted by jclancy
What are the long and short term consequences of having a return of the size I do?
High temperature rise, bad for heat exchanger and for other parts that operate outside of their specifications. Poor efficiency.

High Static Pressure, bad for blower motor and blower wheel.

High Temp Cycling, bad for efficiency and shortens equipments life span.

Overall, you are going to have a problematic unit that ends up costing you money in operating cost, repair costs, and the costs of your personal frustration EVERY time the unit has a problem.

Etc, etc,.....

It needs to be ADDRESSED!
Till the unit is properly tested, everything is just a guess. Get the test results and go from there. I will say that I have a pretty good idea what the results are going to be.

Good Luck.