Air To Water Heat-pump
Air to Water Heat Pump Boiler's operate by collecting the heat energy in the outside ambient air and transferring it into water via a internal heat exchanger. These units work out well if you are not on the gas grid or have no facility to use ground source heat pump's. This technology is not a recent thing but is only starting to become viable with spiraling energy costs. Most Air Heat pump's operate down to temperatures as low as -20DegC so will still operate in the coldest of climates.