I'm still in the planning phases of my build (mostly due to weather not cooperating with my off days from work!) but I am having trouble figuring out how to calculate my heat load. I've seen rough estimates of 40 btu per sq foot for my area of the country (western KY), but I have no idea what I need for the domestic hot water. I know the BTU ratings of the heat exchangers are the max output of that particular exchanger per hour, but how do I know what I need exactly? My house is 1800 sq feet, fairly well insulated (built in 2004) and I plan to run the plate heat exchanger for domestic water heater in series first, then to the heat exchanger in the ductwork, then return to boiler. The water heater is 82 gallons. I was thinking about using 1” pex for the whole loop (roughly 130 feet each way with a TACO 0015 3 speed), until I saw that 1” pex is only good for about 7.5 GPM, which would likely be about 75,000 BTU per hour, if what I read was accurate. I’m not sure that would be enough. Should I opt for 1” pex-al-pex or Logstor to get higher GPM or am I over-estimating what I will actually be seeing for heat load? Some help or direction with accurately calculating my heat load would be really appreciated. Thanks in advance.