This paper provides an analysis of heating from the point of view of the total energy system from the very input of primary energy until it reaches the end-users. In order to minimize the personal judgment in cost allocation between heat and power, the methodology of exergy-based Specific Consumption Analysis proposed by the author is used to evaluate the real consumption of the unity end product in respect to both fuel and monetary cost. Following this methodology the key factors affecting the emission level of a heating system are revealed. It is found that in some applications a total energy system of heating with a specific primary energy consumption as low as 5-15 kg c.e./GJ may be attained. The concept of the 'reversible mode of heating' is introduced and is seen as the basis of ultra-low emission heating systems.