Update:
The outdoor temperatures have been more consistently cold over the last week or so - with some days low 30's for highs and low 20's for lows. I can tell how hard the hydronic system has to work based on how low the water heater temperature gets while it is heating. At these temps, it is not having to work hard at all. When the thermostat calls for heat, it only takes a few minutes to bring in back to the set temperature. The water heater normally stays within 10 degrees of its setting.
Our planned trip to Calgary, Alberta is now a planned trip to Florida (son decided to snowboard with friends in Vancouver instead). So, I know the hydronic heating system will work down there.
I'll post more when we get temps closer to zero - probably soon.