Systems, methods, and apparatuses may involve a burner configured to burn gas to produce burned gas and output radiant heat. A gas valve controlled by the system can regulate the flow of gas to the burner. A heat exchanger associated with a thermal cycle can be used to heat a working fluid of the thermal cycle. The heat exchanger positioned out of a convective heat flow from the burner. A heat valve between the burner and the heat exchanger can be selectively adjustable to adjust heat transfer to the heat exchanger.