I've seen many
reports that indicate that variable speed DC motors are prone to much
more frequent failure. There is not only the motor but the power
control circuitry that can fail and to replace either costs a lot more
than a std motor.

The motor it self rarely fails. Most often it is the electronic module
that mounts on the motor that fails. Most manufacturers now sell the
module separately as a repair part. We usually just change the module.
It is faster than replacing a standard motor, so the labor cost is
lower. Even if the module costs more the total cost is about even. The
variable speed motor ramps up to speed more slowly than a standard
motor, so you don't notice a blast of air when it starts. If it is set
to enhanced mode it dehumidifies better. It is also quieter and more
efficient. I would recommend a variable speed blower on most
installations.

However, I question why the Carrier dealer bid a larger unit. I hope
he did a load calculation. If he just bid by the 500 sq ft per ton
rule, the benefits of variable speed will be lost. Did he just measure
floor area or did he also measure walls, windows, doors, etc. Did he
check insulation levels. If he did not, then chuck his bid and get
another opinion. Depending on where you live, I would question why the
Rheem guy only bid an 80% furnace. If you are in a cooling dominated
climate he needs to bid hiugh efficiency A/C. If you are in a heating
dominated climate, he should bid a high efficiency furnace. The only
time I would want both units to be standard efficiency is in a very
mild climate that uses very little heating or AC.

Stretch