Substituting a solar concentrator for a conventional burner for heating is desirable. However, the sun's energy is diurnal and cannot be counted upon even during daylight hours. To ensure heating is available, a combustor can be provided. According to the present disclosure, a heat exchanger element of the heater assembly is directly acted upon by solar rays via a solar concentrator and by combustion. The heat exchanger also acts as the combustion holder when the burner supplements or supplants the solar radiation. Fuel provided to the outside of the heat exchanger is adjusted based on the demanded for heating and the amount of insolation (rate of delivery of solar radiation) achieved via the solar concentrator. The heat exchanger can be part of a conventional heater or a heat pump for heating water or air.