A good HVAC contractor will create a design based on your building and location, and it will cover 99% of average days efficiently for heating and cooling:
For the remaining 1% it will basically have to run all the time to keep up. (In any given year you may not even get below/above the average outlier 1%.)
As page where you can enter some numbers:
* https://www.heatpumpswork.com/cop-target
Also, given a US zip code, how often the temperature may drop below 15F / -10C (which is a cut-off for many units):
* https://www.heatpumpswork.com/cold-days
A good HVAC contractor will create a design based on your building and location, and it will cover 99% of average days efficiently for heating and cooling:
* https://www.greenbuildingadvisor.com/article/design-temperat...
* https://www.airequipmentcompany.com/2021/what-does-design-da...
For the remaining 1% it will basically have to run all the time to keep up. (In any given year you may not even get below/above the average outlier 1%.)