I understand what you're saying about the loads on the boiler. In the summer the 1 ton per four months is used entirely for hot water production. That includes keeping the boiler water at temp. During the winter the additional load for DHW shouldn't come near requiring an additional ton of fuel every four months. At least I think so.
I wouldn't have the foggiest idea how to calculate the additional load for DHW during the winter months.
Thanks for the idea of putting a temp gauge in the hot water supply. I like it and undoubtedly will install one as soon as my other projects are done. If you have any other ideas on how I can operate my system more efficiently toss them out. I love running things as efficiently (inexpensively) as possible. I'm thinking next summer of wrapping the boiler in an insulation blanket like a water heater. During the winter I like the idea of the heat bleeding into the basement. It has kept the dampness down. My tools all of a sudden stopped getting surface rust on them.
How big is the tempering tank on that system you just installed? I didn't install one on my system. Letting the cold water warm up to room temp before going into the boiler sounds like a good idea.