You're assuming that the water cools instantly and you're always wasting the run from the boiler to the fixtures. No, I'm just assuming that the definition of

You're assuming that the water cools instantly and you're always wasting the run from the boiler to the fixtures. No, I'm just assuming that the definition of a "cold start" is that the water is allowed to cool before the next measurement is taken. The alternative (which I agree is common) is a "hot start". The author defines these terms on the box on the bottom left of Page 76 (which I don't seem to be able to copy and paste). Since the chart explicitly says "cold starts", my question/complaint is that as labelled, I can't see how the chart can be correct. I agree that measuring a blend of hot and cold starts is probably a better metric to judge the systems by.