Heating, Air Conditioning, Fridge, HVAC/Home generator capacity


2 contractors have given me completely different proposals as to how large a home generator I need.  The issue is one of our air conditioning units.  According to the plate on the unit its LRA is 169, which is apparently high.  One contractor tells us that would require a 30kw generator (He is including some other circuits as well, but the driver of the recommended generator size is definitely the high LRA on the AC unit.)  The other contractor says that he doesn't size the generator based on the 169 locked rotor amps, and that all we need is a 20kw generator.  Is one or the other of them right?  Are there other issues I need to be considering?


I am in no way an expert on generator sizing...
I can speak from experience though...
I had a 15 kw run my entire house with one 4 ton a/c unit.  I had nat. gas to the water heater, stove/oven and the dryer.  I limited what was turned on due to fuel usage (gasoline), but, none the less, I could turn just about everything on.  I did notice that at times when the a/c would turn on the voltage drop was enough to cause the computer to reset along with other electronics.  When the a/c was off, it normally ran about 50% or less load.

Things you need to consider.

You mentioned air conditioners?  Can the smaller unit handle BOTH/ALL units coming on at the exact same time (both peaking at LRA)?  Do you plan on running all of them?  Can it handle the load of all of them?  If there is an auto switch over, install timers on the units to try and ensure they can not start at the same time.

Installing starting components (ie hard start kit) on the compressors will help with the LRA and stress the generator less. They also help when on normal power too...

Do you have UPS on the computers and other electronics to protect during a power surge?

Bigger is not always better, but if you have the funds or it is important enough, then I would go with the bigger unit.  Otherwise, I would try to limit to just the minimum to survive on the smaller unit.


Heating, Air Conditioning, Fridge, HVAC

All Answers

Answers by Expert:

Ask Experts


Craig HVAC Expert


I have been in the HVAC field for the past 18 years. I can help with most HVAC questions. I work on commerical buildings for the most part, and have yet to find anything I could not troubleshoot and repair, when repairable. I work on small 1 ton units to a 2500 ton chiller. Troubleshoot air flow, elect, and control problems. I attend regular classes to keep up with the latest and greatest.


I work on commerical sites, hospitals, gov't buildings. I can troubleshoot just about anything in the HVAC business.

5 years trade school, VFD training classes, Liebert factory training, some York and Trane factory training.

©2017 About.com. All rights reserved.

[an error occurred while processing this directive]