Tankless water heater to heat baseboard heat in house.

I am not aware of tankless water heaters for the purpose of heating your home.  My tankless experience was not good.  I wrote about it here: 

http://solarjohn.blogspot.com/2007/10/environmentally-friendly-products-are.html

John

Craig,
It is not a good idea to use a tank less hot water heater to heat your house for several good reasons. The water on demand systems are designed to run for short periods of time heating a house usually demands a longer one time. It shortens the life spam of the tank less heater. And almost all MFG will void the warranty if used to heat a house. 
Like the previous post most baseboards need at least 140F-180F temp on the other side radiant floors can use low temp water anything above 70F. I have tried using a low temp in several baseboard applications 120F to 130F you might get some heat from the baseboards not usually not enough to heat a room to comfort level for most people.
If you want a small compact high efficiency boiler I like the NTI Trinity Gas boiler. You can add an option for DHW on demand.  I know several people who have installed these boilers and love them.  A friend in northern WI install one last spring and he said a typical year he would have to filled his LP twice by Dec and so far this year he has only filled once backing April and looks as if he can make into part of next year.

http://www.nythermal.com/Products/boilers/gas/trinity.htm