I will describe experiments on superconducting quantum circuits combined with an ultrasensitive calorimeter. The heart of the calorimeter is a thermometer capable of measuring local temperature down to microsecond time scales. Experiments on quantum limited heat transport, heat valves and refrigerators based on superconducting qubits will be presented. A detector with noise down to that dictated by the fluctuation-dissipation theorem gives a possibility for continuous wideband single microwave photon detection.