John

I'm already familiar w/the 20Kw Generac, so I Googled Onan. Unless I don't understand what I read, it looks like the Onan is completely different than you assume? Am I reading the right specs?

http://www.cumminsonan.com/residential/products/homestandby/compare?gensetId=110&detail=true

First of all, it's a water-cooled 20kw. Then it also says it spins @ 3600 rpm because of a 2-pole armature. I think their RV models are 4 pole for noise reasons, but maybe they don't go up to 20Kw? I'm guessing if I had a choice on standby generators, I'd choose air cooled over water cooled. I think the overall maintenance would be less on the air-cooled. Now, if one is expecting thousands of hours of operation from it, then the water cooled would have longer life, I'd assume.