Patent ID: 7628337

Claim:
A heating system comprising: a furnace having an air circulator and a heat exchanger; a water heater having a hot water supply and a cold water supply; a supply passage connecting the water heater to the heat exchanger, for conveying water from the water heater to the furnace; a return passage connecting the heat exchanger to a lower end of the water heater at a location that is independent from the cold water supply, for returning the water to the water heater, wherein water within the supply passage has a higher temperature than air within the furnace, such that the temperature of the air increases when the air passes through the heat exchanger; a control to control water flow within the supply passage and water flow within the return passage, wherein the water in the supply passage has a first temperature and the water within the return passage has a second temperature, the first temperature greater than the second temperature, the control includes an electronic shut off valve to prevent water flow through the supply passage and the return passage based upon an air temperature in a building reaching a first threshold air temperature, the control switching on the furnace based upon a second threshold air temperature in the building, lower than the first threshold air temperature.