natural gas in the home, could supplement with gasoline/propane as needed
hot as fuck, it was almost 100 just this past Monday. Low is usually in the 30s
good airflow, cleaner than it probably looks. no cobwebs or leaves
junction box would be the other side of the house. yes to file and water
no idea, I would need to grab an electric bill
yeah, can almost stand up under there
Natural Gas will require a new meter & line run. I did this with mine. My opinion is that NG is the best option because you'll have fuel as long as the compressor stations are operating (and will likely have fuel even for a couple days after they go down).
For really hot areas I like water cooled standby generators. They're going to cost more but the engine will likely last longer & they won't(shouldn't) use nearly as much oil as an air cooled. I wish I would have gone with a water cooled unit when I did my whole house generator. I use a VERY good oil that isn't really to manufacturer specs (more viscous at high temperature) but is FAR more sheer stable, FAR less volatile (turning into mist/vapor) & has better cold flow properties. I use this to increase lifespan & reliability & has worked out well.
I'm not completely sold on the under deck location tbh. Personally, I'd want something I can easily get to as if you're out for several days, you're going to be under the deck to shut down the unit & check oil levels daily. You'll also be under that deck during service intervals. The ability of that space to retain NG in case of a leak would also give me pause.
My area gets really hot (>110 in the summer), my house is also under 2,000sq'. My generator is an 18kW. It can & has run the entire house. I do have a load monitoring system that will drop my HVAC load if the generator becomes overloaded. I just make sure not to do laundry during generator runs & I've never had to deal with loss of HVAC.
My generator is a Generac. I wanted to get a Cummins but the company Cummins & Kohler never returned my calls/emails so I went with Generac. Total cost for mine, including all new NG line, service sub panels, etc was $20k.
Cummins and Onan have merged within the last few years. Onan, IMO, had the best relay packages & Cummins the best engines. Should be a perfect combination; if your local Cummins dealer is worth a shit.
My opinion on the Generac is the new air cooled V-Twin is a solid engine (now has hydraulic lifters so no lashing valves) but I think the generator itself will likely crap itself before the engine as I don't see a way to replace the brushes. Generac is everywhere though & parts are easy to come by if needed. That also makes a big difference.
Personally, if I was looking for a standby generator in a hot area with a decent sized house, water cooled 23-28kW.
Let me know if you would like to know more.