Hey Jeff,
This is a good question, here is my feedback.
I am an electronics tech, I am familiar with both generators. I have a Generac at my house, I have friends that have Kohler, both are really reliable and run really well. Here are some things to consider from my experience:
- I have a Generac 13KW nat gas generator. In short, it has been nothing but terrific. Care has been changing the oil, air filter, and a couple easy to do adjustments (like speed). I installed it in 2005, and it has kept us thru many power outages, a couple of them were 3-day events. Didn't miss a beat. (we get 1 to 3 power outages a year). It does have a little bit of rust on the bottom of the cabinet on the outside, that's about the only complaint I have. The area where I have it does not see a lot of sunlight.
- Friends with Kohler, very much the same. No issues, very solid and reliable.
- I can tell you that Generac seems to deal with service with their dealers, and it seems that getting parts outside of the dealers is impossible. I have not needed that, so no issue yet. If/when I need a new generator, I might consider Kohler because of that, however this thing has been bombproof so it will be hard to change. I like the option of fixing things myself which I most often do. So if you are a 'fix it myself' type of guy, you may want to consider Kohler. Otherwise, find a dealer that services Generac (not all do) and has a good reputation, then sit back and don't worry.
- If I remember right, propane delivers a bit more energy than natural gas, so you may get a KW or two above rated if running propane.
- Propane and Nat Gas powered generators are remarkably simple. You have an airbox, then the rest of the engine. Because of that they are pretty reliable. Do your maintenance, err on the side of changing oil early and you will get alot of life out of it. It's now 17 years later, I still have trouble seeing the oil level on the stick after an oil change because the oil stays squeaky clean.
- THIS PART IS IMPORTANT - when sizing the generator most people try to go 'whole house' or get almost every thing in the house on it. If you are looking just to ride thru the occasional power outage and cost is not of concern this may be the option for you. HOWEVER, what most people do not consider is this: Duty cycle during an extended outage. I deliberately sized my unit to run essentials and have a bit of over head for some 'nice to haves'. I have a 3,000 sq/ft house, run it just fine on a 12KW unit. I could have done a 'whole house' at 20KW+, glad I didn't. Here is why:
If you have an extended outage, your gas bill will be expensive. Like I mentioned we have had ~numerous~ 2-3 day outages where the generator was running non-stop. Our gas bill was indistinguishable month-to-month when we had those events - really impressed my wife who watches that stuff like a hawk. IF you are experiencing multi-day outages frequently, or getting a generator to get thru a potential 'SHTF' event (down for weeks) you may want to consider that especially if you are having propane delivered - will make that last twice as long. I have nat gas so when the power goes out there is more for me - no issues, a virtual continuous supply.
The smaller KW units are cheaper, are widely installed (means parts are available), and run terrifically well. Some have optional features which you will be easily ready to afford as opposed to getting a big unit. Those are not cheap.
Do a survey of what you can and can't live with. I live in PA, can do without the AC. Not without the furnace. Need the septic pump. Can do without lights in the kids bathroom. I can say that when the lights go out we don't really miss much. We were the envy of our neighborhood. We had lights as they were loading up their freezers to take to other people's houses....till they got their own generators.
Good luck with your installation.. Hope this helped.
BJ