[quote="markviii"]I don't know who told you there is no need for an expansion tank on a closed hydronic system, but that is flat out wrong. You definitely need to add one to the system, and it will need to sized for the house sytem + the S260. An Extrol 90 or a floor-mounted commercial expansion tank would be my choice. You can tie the S260 in by putting another set of closely spaced tee's in your primary loop.
Also, I hate to be the one to tell you this, but 1" pex can effectively move about 80,000 btu's per hour. Hopefully that is enough to heat your home! The S260 will be loafing most of the time unless you plan on connecting additional loads to it in the outbuilding.
One more question...how is your domestic water heated?[/quot
The domestic water is heated by another but smaller tankless water heater. I ordered the 260 with a domestic coil to take care of it. Currently there is approx 4500 sq ft that I'm heating and will be adding another 1000 sq ft next year. I can't believe all the diff stories Ive gotten on what I need and don't need. I'm not talking about you. I'm talking about a few " professionals" I've asked.
What size pex would you recommend? I bought this place in April and it is as you see it. The former owner used 2000 gallons of propane last winter and I wanted to save some money. I hope this all works out in the long run. Thanks for the help and please keep it coming