A loose rule of thumb... and we should NOT follow rules of thumb:
It takes around 3 times the watts to START an elec motor as it does to RUN the same motor. Whatever your run watts are (volts x amps)... then 3 times with some wiggle room probably will work.
I agree with Motoguy... a larger unit is a better choice. Remember that generally speaking: A generator will produce close to the same watts on LP gas as gasoline... yet around 20-25% LESS on NG.
Have a LICENSED electrician handle this for you.
Galatians 2:20-21; Colossians 1: 21-22 & 26-27; 3:1-4; Romans Ch's 5-6-7-8
2 Chronicles 7:14
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