This AUTOTERM Flow liquid heater is a compact, fuel-powered hydronic heater with a 5 kW heating capacity, 12 V DC supply, and petrol operation. The FLOW 5B is designed for heating coolant circuits and can be used in boats, yachts, cars, vans, and motorhomes. It can be integrated into systems for engine preheating, water heating, and cabin heating via suitable radiators, fan coils, or the vehicle's existing heater.
A separate electric circulation pump pushes the coolant through the heater's heat exchanger, while a pulse-controlled dosing pump supplies fuel. The optimal fluid volume in the system is 10–12 liters. The coolant flow is 1,200 l/h at 0 bar and 800 l/h at 0.18 bar system pressure. The heater has Ø18 mm coolant connections, and the heater unit itself measures 220 × 90 × 136 mm.
The electrical power consumption is 42 W during operation and 122 W during startup. Petrol consumption is up to 0.70 l/h, and petrol according to EN 228 must be used. The built-in voltage protection shuts down the 12 V model at voltages below 10 V or above 16 V. Sensor monitoring and automatic shutdown also provide protection against overheating and faults in the coolant circuit.
The heater can be mounted in a 0° or 90° position with the air pump facing upward, and the mounting bracket can be positioned horizontally or vertically. It must be installed below the level of the expansion tank in a dry, ventilated, and protected location. For marine installation, the exhaust outlet must be placed at least 60 cm above the waterline and protected against water ingress. There must be at least 20 cm between the combustion air intake and the exhaust outlet.
The installation kit includes thermal insulation, a fuel pump with clamp and rubber seal, wiring harnesses for the pump and control panel, an air intake hose with filter, a 1 m exhaust pipe, a 5.5 m nylon fuel hose with protective cover, a pump bracket, an airtight silencer with mounting kit, heat protection for the exhaust pipe, an electric fluid pump, a coolant hose coupling, an L-shaped exhaust adapter, and a 2 m coolant hose.
A control panel is required and must be purchased separately; the digital panel with item no. 50.251.01 can be used. The installation also requires additional hot water hose, including item no. 17.740.16, as well as heat emitters as needed. Fan coils 50.267.01, 50.267.02, 50.266.01, and 50.266.02 are documented for use with the system. For the exhaust, the Ø24 mm hull fittings 50.255.01, 50.255.02, or 50.255.03 can be used.
For boats, the heater is recommended for 10–13 m in Mediterranean climates and 8–11 m in Nordic climates. Regular inspection of electrical connections, hoses, air intake, and the exhaust system is recommended. Outside the heating season, the heater should be activated at least once a month for 20 minutes.
Key featuresHydronic liquid heater with 5 kW heating capacity
12 V DC version for petrol according to EN 228
Max. fuel consumption: 0.70 l/h
Electrical consumption: 42 W during operation and 122 W during startup
Optimal fluid volume in the system: 10–12 l
Coolant flow: 1,200 l/h at 0 bar and 800 l/h at 0.18 bar
Heater unit dimensions: 220 × 90 × 136 mm
Electric circulation pump and fuel pump included
Automatic voltage, sensor, and overheat protection
Control panel and additional installation components purchased separately
