I took great pains to setup my boiler to run nearly continuously by using its outdoor reset controls and an outside temp sensor (a simple 10K NTC) to adjust the

I took great pains to setup my boiler to run nearly continuously by using its outdoor reset controls and an outside temp sensor (a simple 10K NTC) to adjust the flow temperature to match/ever so slightly exceed what’s needed to match the building heat loss. This results in higher efficiency and better steady state comfort as the heat is on for always 18+ hours and often 22+ hours per day. It’s hard to say with confidence on the precision, but it seems like this is saving 8-10% in gas (in therms) vs last year when I had a constant flow temp (that I’d adjust manually every so often to try to match but where I’d have to leave it “too high” or risk a cold house on the coldest days). The exhaust temps in the stack reach steady-state far before even a 30 minute run would be finished.