We connected the pumps to a timeclock and only run the heat for roughly 2-3 hours a day depending on the time of the year
It's a little colder than that, here. We also can't use a normal water heater because they won't stand up to the constant circulation and fail after a few years. It gets down to -40c for a couple days every year and -30c isn't unusual for a week or two. For the guys from southern US, Fahrenheit and Celsius are the same at -40. It's about the same weather as North Dakota.
We often have a main circulating pump that just circulates through the boiler (hot to cold), and the remote heating loops draw from, and return to, the main loop. Is that what you're describing? The specs I read were that the two sides of the remote loop must be within inches of each other. I think it's to stop the return temperature from being too cold and causing condensation of flue gasses.
I understand about the time it takes to warm up a system with a lot of mass. In-floor heat has the same problem. It also has a cool down problem. Forget about night set-back on the thermostat. It's a definite draw-back.
