Me too. I have several smaller UPS systems as I did not want to rewire for dedicated circuits all over the house. I have a 15KW Onan (surge to 18kw)in the back yard with auto start and on-load and off-load testing.

During cold weather the start/throttle /transfer time is about 15 seconds max. We do have the HVAC fan on auto transfer but we automatically disable the compressor. WE have gas heat so the system will easily run the T-stats,gas valve and air handlers.

The usual cost of a high capacity UPS and the battery maintenance costs are too great for many folks. Batteries DO have a shelf life.