Hi All,

I have an electric furnace that I recently upgraded to a heat pump.

The furnace is a Carrier FH4B003. It had the motor speed set at medium for the electric heat strips. The tech set to high speed after heat pump installed (2.5 ton rheem w/3 ton coil).

I measured external static pressure of 0.5" WC at return plenum, and 0.0" WC at discharge plenum, so I assume I have a total of 0.5" WC and supply ducting is of adequate size. Please correct me if I am wrong.

Furnace nominal flow is 1700 cfm.

There is a chart for airflow at different speeds.

At 0.5" WC @ 230volts, HIGH = 2106 cfm, MED = 1890 cfm, LOW = 1467 cfm.

There is another chart for airflow with coil(Carrier not one I have.) 0.5" WC @ 230volts, HIGH =1555 cfm, Med =1485 cfm, LOW = 1360 cfm.

My heat pump and a-coil give ARI cooling performance specs at 1050 cfm.

My question:

I would say I need to have fan at low speed for maximum efficiency, and If so should tech be called back out to check charge at new lower speed?

Also, this is a downflow furnace, and there is no trap on condensate line. I think I need one. Drain line only goes about 3 feet before exiting garage to outside.

Thanks.