They assumed a family of 4 in the local area where incoming water temperatures varied significantly by season.  

They canvased the whole city taking temperatures.

Here are just a couple less considered items:- We specify minimum and maximum temperature.

I had a septic system on a multi family rental in New York State.. it freezes during extreme temperatures and sometimes backs up.

For example, my gas gun from the factory was setup for 200k btu's. my heater is only 130k btu, so you have to follow the directions and set the gun to match the boiler rating. also, if you are dealing with steam, be careful as steam boilers don't so much work on temperature, but rather pressure.

All things not working on move-in:A/C unit for upstairs broke in 115 degree Vegas heat, fixed in 2-3 daysCould not change temperature of thermostat, it was pre-programmed and controlled remotely, months to fix No internet, after we spoke numerous times about us working remotely from the home via the internet, added next dayNo garage door opener, 2 weeks to getNo heat (yes we need heat in Vegas), took weeks to fixShower in 4th bath did not work, months to fix but wasn't urgent as we were not using it No dishwasher, still not fixedWhile everyone has tried it has been a huge inconvenience with all the repairs and the dishwasher has never worked and still doesn't.

The dog or 4 year old chewing on the porch rails, window sills, stair rails and claiming 'peeling paint' which can not be painted outside until the temperature comes up. 

It has one furnace and one thermostat in the down unit that controls the temperature for the entire house-both units.

A properly operating AC should not freeze up just because the unit can't reach the set temperature.

It takes more energy to go back to the desired temperature that way.