I recently bought a house just outside of Boston with radiant floor heating that used an electric micro boiler just for the heat. The house is 1200 sq ft with one bathroom, though we hope to add a second in the next year or two. The hot water for the house (showers, sinks, laundry, etc) is done by the traditonal electric hot water tank. The micro boiler for the radiant floor heat has to be replaced now.

I have gotten several estimates on replacing the boiler for the heat and they have recommended a combi boiler (such as the Rinnai EC 110) for the radiant floor heat and to also produce on demand hot water for the house. The last estimate I received said we would be unhappy with just a combi boiler and recommended putting in a high efficiency boiler (Bosch Greenstar 100) for the heat in combination with an indirect tank for the hot water. The last plumber's reasoning was that as we shower, did laundry, or used the dishwasher the combi boiler by itself would divert water from the heating side and the house would cool off until we were finished with the hot water.

Does anyone have recomendations on using a boiler and indirect hot water tank vs. just using the combi boiler for both hot water and heat?