Among other things, I'm trying to shake out the details for my domestic hot water generation. First off, what is a good number (gallons per minute) to shoot for? We are installing an 80 gallon whirlpool, and have three showers in the house. Somewhere from 5 to 10 gallons per minute seems reasonable. It seems that 10 might be better with no DHW storage, and 5 would be fine with a buffer (like an indirect tank). I'd rather stay away from the expense of a tank if I can. The boiler will be a Tarm 40 or EKO 40 tbd in the next few days. Either way, I'm generating 140,000 BTUs/hr at full burn. I'll have a water storage system...1000 gallons of pressurized storage if I can find a used propane tank in time, or 800ish gallons of open vessel if not. If I was to use a flat plate heat exchanger to retrieve DHW, how do I go about picking a size? Water on the hot side would be 180 if the boiler or backup (propane) boiler were on line. If the boiler was cold, water would vary from 110 to 180 depending on the storage tank temp. Can I take 50 degree well water up to 120 (or 100 if the tank is cold) with a heat exchanger? I assume I could also recirculate flow from a tempering valve on the exit side. Would I have an aquastat call for the propane boiler if the wood side can't get the DHW up to 120?