Abstract: A method for operating a heat pump (1) that transfers heat to air flowing through ventilation ducts is provided. An outside temperature is acquired. If the outside temperature is higher than a limit temperature, an operating time of an electric heating register (2) of the heat pump (1) and/or an energy consumed by the heating register (2) is acquired. If the operating time exceeds a first limit value within a set period of time and/or the energy consumed by the heating register (2) in the set period of time exceeds a second limit value, a message is output.

Abstract: The invention relates to a boiler comprising a combustion chamber which is surrounded at least in part by a combustion gas flue that is embodied as a primary heat exchanger. The combustion gas flue is enclosed at least in part by a water-conducting housing while a water-conducting secondary heat exchanger that is hydraulically connected to the housing is mounted downstream of the combustion gas flue. According to the invention, the combustion chamber is surrounded at least in part by the secondary heat exchanger.

Abstract: The invention relates to a boiler comprising a combustion chamber which is surrounded at least in part by a combustion gas flue that is embodied as a primary heat exchanger. The combustion gas flue is enclosed at least in part by a water-conducting housing while a water-conducting secondary heat exchanger that is hydraulically connected to the housing is mounted downstream of the combustion gas flue. According to the invention, the combustion chamber is surrounded at least in part by the secondary heat exchanger.