ScottSeile wrote:no clue about heat loss as yet....baseboard heat.
Is your new home going to have a large soaking tub or a two-showerhead shower? With a new home such as yours, the BTU capacity required for domestic hot water often exceeds the space heating load. Make sure you factor the DHW into your calculations.
Yes, the EFM DF520 can accept an oil burner - but it is a manual-switchover from one fuel to another, and the efficiency on oil leaves something to be desired. My preference is to have a separate oil or gas boiler for backup, but not everyone has the floorspace or chimney(s) for that. You ARE planning on putting up a chimney right?
ScottSeile wrote:Another question is will the boiler HW be too hot for PEX tubing?
Generally no, but if you use a boiler that is prone to temperature overshoots it is easy enough to install a mixing valve and "temper" the water.