wa8yxm wrote:
Half a horse power (Common blower size) is 500 watts running (Approximently, I know that's not the right math but the motor is not 100% efficient so that's what it takes) starting can be 2500 or more.
OP has a 35K BTU 90+ furnace.
It won't have even a "half horse" fan motor.
Even though the furnace documentation may not be the same as the OPs (since they didn't give model, I guessed using documentation for any newer high efficiency furnace) I suspect the that small of furnce will have similar limited CFMs which does not require a large motor. The one I linked states 1/3 HP motor, by pure math 1/3 HP would be roughly 250W or 2 amps at 120V. This is very doable with a small gen even a 1000W gen should be able to run that furnace.
If OP furnace was larger like 75K BTU then yes, a much larger fan motor would be required and employed in order to get the correct CFM of airflow. 35K BTU furnace does not require a huge amount of airflow and hence a much smaller fan motor can be used.
The OP also clearly stated that their 35K BTU furnace is using ECM type of motors.
You can read up on ECM motors
HEREECM motors by their design do not have a large startup surge, they are actually soft started.
"An ECM motor, known as Electrically Commutated Motors, is the fastest it has ever been, with unparalleled airflow delivery to meet the necessity of a heating or cooling system. It can be used in hundreds of different applications. It is a self-regulating motor that do not need the assistance of any other system to operate. But what causes an ECM motor to work? How does the motor know when to speed up and when to slow down without external sensors to track pressure, temperature, or something else?
ECM motor has a microprocessor which is a crucial factor in its ability to have higher performance. The microprocessor is used to sequentially energize and de-energize each winding of the stator, generating an electrical current. The processor-based pulse control generates a magnetic field, which allows the rotor inside this ring of magnets to spin. The microprocessor employs a closed-loop feedback system to more accurately regulate the magnetic fields, thus reducing the eddy currents and losses experienced by conventional mechanically commutated motors. This also allows for the use of a brushless motor, which reduces points of physical contact within the motor’s moving parts and makes them more durable.
"Think of a ECM motor as more like a DC brushless motor like what is typically used in computer fans, only on a much larger scale. It is fully RPM controllable from start up to full speed and back down to zero without large startup currents.
