Abstract: In a large vehicle, such as a bus, a fuel-fired coolant heating system. The heating system uses a heating unit to add heat energy to the coolant, which is then circulated to heat exchangers throughout the vehicle. Safety features in the system include an impact switch which immediately stops the flow of fuel to the heating unit in the event of an accident. Another feature which contributes to safe operation of the system is the presence of a deaeration tank in the coolant flow path. The tank allows for the removal of air so that air locks can be prevented and is fitted with a pressure relief valve should overheating occur. Finally, service and inspection of the system is facilitated by attaching components of the system to a slide panel, which can be pulled out of the side of the bus. By making the components of the system easily accessible, problems are generally avoided and safety is, therefore, improved. The heating unit for use with the present invention is one which is available from Espar Products, Inc.