Whole house generator/ HVAC question

Wife and I are starting to explore a turnkey whole house generator install.

Getting too old to deal with our Troy-Bilt 5500 rollout.

House is 2100 sq ft ranch with unfinished basement walkout.

Question is regarding our dual feed HVAC setup.

It’s an auto transfer: heat pump over 35 degrees, tanked propane under 35 (500 gallon capacity tank).

Generator would be propane fed all year (when power is lost).

2007 Trane equipment.

Are any of you familiar with the potential consequences of such interfacing with a whole house?

Would likely be in the 22kw to 26kw range.

I have pending on site appointments with both Generac and Kohler.

My first contacts with both seem to be in the dark on such a dual feed setup. All they can really say to is: wait for the on-site analysis.

I don’t know anyone who has had such a setup, nor can I find anything online that relates.

Thanks for any input.

I don’t want to walk myself into trouble on a 15k to 20k investment.

Generac and Kohler are the same units. One of them makes it for the other company. I did not go with the whole house unit and saved $4K (about 5 years ago).

We have a well, furnace and about 3/4 of our 2400 sq. foot home on the generator. 2 fridges and a freezer included. It is a Generac 10kW unit and we have no issues at all.

Be advised, - a service contract is not needed. The installer wants $300+ for a yearly oil change and plugs/air filter. Parts on amazon run around $30 plus 1.6 quarts of synthetic oil.

Seeing how the generator will just be standing in for utility power I don't see how the heat pump would act any differently when on generator then on utility power.

Let us know if you find out anything different.

FWIW, I have a 9000W for power outages: 1652 SF house, 2000 SF of shop, but no AC.
Runs everything just fine, though I do scale back activities like laundry & microwave at those times.
It's likely close to the limit, judging by the load I hear from the generator if I run those items + the normal stuff.
Seems everyone else has a lot larger setup than mine, but maybe this will serve as a reference.

Unless something has changed REAL lately, this is not true. I have a Generac and my buddy has a Kohler and there is NOTHING even similar. Kohler has a better following from a reliability perspective, while Generac is the sales leader mostly because they do EVERYTHING on the total cheap. I have a history with Generac and their 'cheapness' with failure of units.

The largest factor for sizing a standby generator is what loads you want to simultaneously support. (Duh) Your heating system is just another load to be considered. Of the two modes, I would guess the heat pump would be the higher of the two and would be the load you would use. Just a caution, one of my friends has a generator in the 26 KW range and at over 130 gal/hr of propane at full load, he upgraded to a 1000 gallon tank from a 500 gallon tank. You would have to run the numbers as to what you think your actual loads would be and the duration of the loads. You can do a lot of this yourself with the equipment specifications and a clock. I don't know how your weather is or how reliable your propane supplier is but where I live you need to prepare for at least a week without power if it all goes to hell.

Compare the sound level at full load for a Kohler vs Generac generator of the same kW rating. The Generac is noticeably louder.

While I'm no expert ,I have to believe this is correct. Mainly because Generac headquarters is about 2 miles down the road from me and Kohler is up in ...well Kohler. My buddy was a field service tech for Kohler for years.....he didn't have anything to do with Generac.

I was a sales engineer for a Kohler generator distributor for 8 years.

+1 for Kohler and Generac being different companies with different products.

This is the answer. Everything downstream of the transfer switch won't know what is feeding it.

I deal with industrial and commercial sized uninterruptible power supplies for a living and we interface between utility and generator power using transfer switches all the time, the load doesn't care in a properly setup system. Just match voltage, frequency and phase rotation, if three phase, and you are good to go.

My heat pump won’t run on my generator. Immediately throws an error. It’s one of them super high efficiency units that is run by a computer.

FWIW, I have a 9500kw (peaks 12,500kw) standby generator that powers a sub panel through a transfer switch. With a clamp-on amp meter I measured the amp draw of my 3.5 ton A/C unit...at startup the meter spikes to 81 amps and then settles down to a little over 10 amps running.

On generator power, the generator noticeably bogs at A/C startup but quickly recovers and handles the load. This test was done in mild weather, don't know how it'll work during a heat wave...amp draw might be higher in hot weather.

Then it's not installed properly, probably the neutral/ground.

A soft start would help

No - its the stupid computer. And I mean its stupid. I have had tons of fun with it. It is really a bad a idea to buy a heat pump that takes all functionality away from you and the stupid computer makes all the decisions for you. And don't get me started on the thermostat control scheme.

And the code it threw was not in any manual I could find.

Had one of those on a previous unit, it malfunctioned and kept zapping even after the compressor was running...never again.

Did you ground your generator?

My furnace did the same thing till I ran a ground for my generator.

I do this for a living, there is something wrong with your installation or possibly the frequency/voltage control of your generator. It is not the computer on your heat pump.