Deaner,
The model I got 13 years ago was called AT-040
Looking at the website, I think it is now called the Premier P040,...
http://www.waterfurnace.com/content.aspx?section=residential&page=products My unit has emergency resistance heaters that will kick on if my well pump breaks - but my well pump has never failed. I installed a large water storage tank to supply the system, ~80 gallons which is a bit larger than normal for residential. The large tank reduces the pump cycles. You can see all the technical info, on the website - they recommend 5 gpm for an openloop P040. You should also get the desuperheater which is probably standard on these systems.
