Zoning and Efficiency of High Efficiency Boilers Operating on Outdoor Reset

I always see high efficiency modulating boilers installed with zoning control. Unfortunately this can't be correct due to the way modulating boilers are designed to operate.  Modulating boilers should operate on outdoor reset, meaning that temperature of the water going to the heating system changes depending on outdoor temperature and flow of the water through the heating system remains constant.

The lower the outside temperature gets, the hotter the water that is pumped into the heating system. When it is warmer outside, the water temperature going to heating system gets cooler.

If one zone is turned off or set to a lower temperature for a period of time then when the homeowner needs this space to go into normal heating mode it will take hours to heat the space to the desired temperature. This space needs a water temperature higher than the one set by outdoor reset control of the boiler to get heat delivered fast. Some contractors bypass this by deciding to program the boiler so water temperature will be raised over the one set by outdoor reset for a limited time to heat this one zone faster. Yes, right, but at the same time other zones will be overheated.

Zoning of systems controlled by outdoor reset cannot be done with zone valves or pumps. It must be done with outdoor reset mixing valves, and reset curves and boosts must be set for each zone. It might be cost prohibitive and impacts efficiency of the system.