Not Enough Return Air?

[jir]

4 ton system, NE Texas, held the 2500 sq ft house at about 78 in recent 12-104 temps.

The question is based on having one in-the-ceiling return from just outside the (remote) master bedroom that is 1 ft x 2 ft and on about a 40 foot run of round metal duct (maybe about 1 foot in diameter - not sure because it has some sort of silver / grey insulation that has what looks like stapled seams holding it on).

The other duct is floor level 2 feet by 1.5 feet - BUT that's just the opening - the return air actually travels up between the sheetrock on the outside and inside of the water heater closet (electric) and has about a generous estimate of 300 sq inches area (plus the added resistance to flow versus being a single open duct). The heat pump is mounted horizonally, with a box (plentum?) built over the water heater closet and with the remote return line coming into that box.

Are the friction losses and the smaller-than-apparent return area a significant concer? The total area works out to be 4 square feet, but given the arragement is that really enough for a 4 ton?

We're contemplating a replacement of the old 8.3 SEER unit and I'm trying to understand what more needs to be done than just removing and replacing the basic hardware...

Thanks for any insights!

[comfortdoc]

The only way to know is have the airflow measured. static pressure readings in supply and return compared to a fan performnace chart for your existing A/H will tell how much air is moving through the duct system.

[udarrell]

The tech needs to do some static testing to determine how the Supply Air static compares to the Return air Static.
There could be static problems on both sides of the ductwork.
Going through the wall areas could create problems.

Do some studing & see if the tech can locate any & all problems that might exist with the system, including the refrigerant system.

http://www.udarrell.com/external_static_pressure_readings.html
- udarrell