I'm getting ready to pick out a backup generator for my house, and part of the process is figuring out "startup amperage" of the electrical motors of the appliances that will be on the generator circuits. I could calculate this if i knew what the HP rating of the motors were... pump motors, fan motors, compressor motor, am i missing anything?

I have a 3 ton climatemaster 27, w/ ecm fan, and a 2 pump QT nonpressurized flow center.

i have backup heat in the form of pellet stoves that will be on the generator, but having the heat pump means having warm, possibly hot water from the desuperheater as well... in my old age i find i like my luxuries.

I'm sure i could get this from the manufacturers, but i'm also sure i'm not this first guy to try this. so i thought i'd pick your brains first.

 thanks in advance!

Startup amps are equivalent to Locked Rotor Amps listed on unit nameplate. It is a big number, on the order of 4-6x full load amps. The good news is that a genny will supply amps far in excess of rated surge kW divided by voltage for the few cycles necessary to start a compressor. For example, an 18kW Generac whose specs I have on file will make 35 KVA at a 35% voltage dip. Despite the dip, the KVA are available to kick start a compressor.

Better news is that there is an option specifically designed to ease the difficulty of running a compressor off grid. Google "Intellistart" and "Securestart" for details.

I have a similar 3 ton geo heat pump and it starts flawlessly with a 24 kW genny. In fact, that is ovekill

For true generator happiness, spring for a 4 pole 1800 RPM model. They are quieter, beefier, longer lasting, and more efficient. We've had instances where my wife was unaware the house was on the genny following an outage

Cool. thanks! everything i needed.