Abstract: A method for regulating coolant temperature of an HVAC heat pump system with coolant heating. The method includes measuring temperature of coolant flowing through the system, and configuring a valve assembly of the system to direct coolant flow to a heater core from both an engine and an engine bypass line when temperature of the coolant is above a predetermined threshold.

Abstract: A compact hydronic space and water heating apparatus and system is disclosed for use in a recreational vehicle. A liquid heating medium, stored within a low pressure tank, is recirculated through a gas fired heater thereby maintaining a desired set point temperature. The liquid heating medium is further circulated through the vehicles hydronic space heaters to heat the interior of the vehicle. Further fresh domestic water is passed through a heat transfer coil within the tank whereby hot domestic water may be provided. An auxiliary heating device is attached to the tank whereby hot combustion engine coolant may assist in maintaining the temperature of the liquid heating medium within the tank and/or reversed to pre heat the combustion engine if and when needed.