A heater assembly, comprising: a solar concentrator; a heat exchanger comprising at least one tube adapted to carry a working fluid; and a window arranged between the solar concentrator and the heat exchanger; wherein: the solar concentrator is arranged to direct the sun's rays onto the heat exchanger; wherein the solar concentrator has a collection area many times greater than an area of the window; and the heat exchanger is disposed within a chamber defined by: a window, a side wall, and a bottom wall; and the chamber is separated by the heat exchanger into a fuel-and-air delivery chamber having a fuel-and-air inlet and a combustion chamber having an exhaust outlet arranged such that fuel and air supplied through the fuel-and-air inlet are drawn through gaps in the heat exchanger into the combustion chamber, with exhaust gases exiting the combustion chamber via the exhaust outlet, wherein the gaps in the heat exchanger are carefully sized to be smaller than the quench distance such that flash back into the fuel-and-air delivery chamber from the combustion in the combustion chamber is prevented. a solar concentrator; a heat exchanger comprising at least one tube adapted to carry a working fluid; and a window arranged between the solar concentrator and the heat exchanger; wherein: the solar concentrator is arranged to direct the sun's rays onto the heat exchanger; wherein the solar concentrator has a collection area many times greater than an area of the window; and the heat exchanger is disposed within a chamber defined by: a window, a side wall, and a bottom wall; and the chamber is separated by the heat exchanger into a fuel-and-air delivery chamber having a fuel-and-air inlet and a combustion chamber having an exhaust outlet arranged such that fuel and air supplied through the fuel-and-air inlet are drawn through gaps in the heat exchanger into the combustion chamber, with exhaust gases exiting the combustion chamber via the exhaust outlet, wherein the gaps in the heat exchanger are carefully sized to be smaller than the quench distance such that flash back into the fuel-and-air delivery chamber from the combustion in the combustion chamber is prevented. the solar concentrator is arranged to direct the sun's rays onto the heat exchanger; wherein the solar concentrator has a collection area many times greater than an area of the window; and the heat exchanger is disposed within a chamber defined by: a window, a side wall, and a bottom wall; and the chamber is separated by the heat exchanger into a fuel-and-air delivery chamber having a fuel-and-air inlet and a combustion chamber having an exhaust outlet arranged such that fuel and air supplied through the fuel-and-air inlet are drawn through gaps in the heat exchanger into the combustion chamber, with exhaust gases exiting the combustion chamber via the exhaust outlet, wherein the gaps in the heat exchanger are carefully sized to be smaller than the quench distance such that flash back into the fuel-and-air delivery chamber from the combustion in the combustion chamber is prevented. a window, a side wall, and a bottom wall; and the chamber is separated by the heat exchanger into a fuel-and-air delivery chamber having a fuel-and-air inlet and a combustion chamber having an exhaust outlet arranged such that fuel and air supplied through the fuel-and-air inlet are drawn through gaps in the heat exchanger into the combustion chamber, with exhaust gases exiting the combustion chamber via the exhaust outlet, wherein the gaps in the heat exchanger are carefully sized to be smaller than the quench distance such that flash back into the fuel-and-air delivery chamber from the combustion in the combustion chamber is prevented.