Webasto Coolant Parking Heaters: How They Work, Models and Rules

How a Webasto coolant heater works

A coolant heater is a compact boiler plumbed into the cooling circuit and running independently of the engine. It works in this sequence:

1. A small fuel pump meters fuel from the vehicle's tank into the combustion chamber.
2. A blower feeds in combustion air.
3. A glow plug ignites the mixture and switches off once the flame is stable.
4. The hot exhaust gas heats the coolant through the wall of the heat exchanger; combustion gases stay separate from the coolant and the cabin air.
5. An electric circulation pump moves the warm coolant through the engine block and the heater matrix with the engine off.
6. Once the coolant is warm enough, the cabin fan blows heated air into the interior and onto the windscreen.

Output of a car water heater is usually quoted at 4–6 kW, reached about 30 seconds after ignition, and the units are designed to start at down to −40 °C (−40 °F). Warm air reaches the cabin later than with an air heater, because the engine warms up first. The benefit is a preheated engine: oil flows more easily, the first minutes of driving are gentler on components, and a battery weakened by cold has a much lighter load at start-up.

Webasto, founded in Germany in 1901 by Werner Baier as a maker of bicycle spokes, is usually credited with its first engine-independent car heaters in 1952. Other manufacturers, for example Eberspächer, build heaters on the same principle.

Coolant, air or electric: which heater type does what

A coolant heater warms engine and cabin, an air heater warms only the interior air, and an electric engine heater needs a mains socket where the vehicle is parked.

For overnight use, an air heater is quick and quiet. A coolant heater needs its circulation pump and the cabin fan, which together draw significant current, so it is not suited to running all night from the vehicle battery.

The Webasto water-heater range at a glance

Webasto makes coolant heaters for cars, vans, motorhomes, trucks, buses, boats and machinery. Figures are from Webasto's product pages, October 2026.

A Thermo Top Evo measures 218 x 91 x 147 mm (8.6 x 3.6 x 5.8 in) and weighs 2.1 kg (4.6 lb), so it usually fits in the engine bay. The Evo Smart works between −40 °C and +60 °C (−40 °F and 140 °F), has an optional altitude kit for up to 3,000 m (9,840 ft) and supports analogue, LIN, CI and W-Bus interfaces. The Pro 120 and 150 are rated up to 3,500 m (11,480 ft). The 24 V units belong on trucks, buses and special equipment.

Fuel types, consumption and battery load

A Webasto coolant heater burns the same fuel as the engine: diesel cars get a diesel heater, petrol cars a petrol one. The Thermo Top Evo Smart is listed for diesel including HVO, biodiesel blends and FAME, and for petrol including E5, E10, E85 and M15.

Biodiesel is where sources differ. Webasto's Evo Smart page includes FAME and biodiesel blends, while general German reference material warns that diesel parking heaters should not run on biodiesel (RME) because of heavy smoke and coking. Older heaters may not share the newest models' approvals, so follow the manual for your specific heater.

Fuel consumption depends on the model, the power stage and the running time. Webasto's product pages give no single litres-per-hour figure, so check the datasheet for your unit rather than rules of thumb.

The blower, fuel pump, circulation pump and cabin fan all draw from the battery. A preheated engine is easier on the battery at start-up, but a short drive after a long heating cycle may not put back what the heater used.

Remote controls, timers and the ThermoConnect app

Webasto heaters can be started from a timer or panel in the car, a handheld remote, the ThermoConnect smartphone app or, on some vehicles, the car's own infotainment system.

• Radio remote: range is usually quoted at 300–500 m (980–1,640 ft), up to about 1,000 m (3,280 ft) in good conditions. Bidirectional remotes confirm that the heater has started.
• GSM or app control: no distance limit, but it needs a mobile connection or a SIM card with running costs.
• Timer: pre-set departure times suit a fixed routine such as the morning commute.

Integrated heaters can sit alongside other on-board computer functions, and the Evo Smart is certified to an automotive cybersecurity standard, retrofits included.

Getting a parking heater installed: checklist

A coolant heater connects to the coolant circuit, fuel supply, exhaust outlet and wiring, so installation is workshop work. Webasto offers vehicle-specific installation kits for many models and extends the warranty on car installations from two to three years when a certified Webasto installation partner fits the heater.

In the EU, permanently fitted accessories without the required approval can affect the vehicle's road registration, another reason to avoid improvised installations. No reliable dated EU price survey was available for this guide; the total depends mainly on the heater model, the control option and the labour time for your vehicle.

Safety, exhaust and EU approval rules

A coolant heater is a combustion appliance, and its exhaust contains carbon monoxide. Never run it in a closed garage, a workshop with the doors shut or any other unventilated space.

Manuals also prohibit operation at filling stations and where fuel vapour can collect. Rules on when and where a parking heater may run differ between EU countries, so check the manual and the local rules, and note that vehicles carrying dangerous goods can face extra requirements.

The combustion chamber is a wear part to be replaced at the intervals the manufacturer sets, and many manuals recommend running the heater briefly from time to time outside the heating season. A heater that smokes, smells of fuel or stops with a fault code belongs in a workshop, as codes differ by model. Other winter checks still apply, from battery condition to winter tyres.

Common mistakes with parking heaters

Most problems come from use and maintenance, not the units themselves:

1. Short trips after long heating cycles. The battery cannot recover, and eventually the heater or the engine will not start.
2. Heating all night. A coolant heater is not made for continuous overnight cabin heating from the vehicle battery; an air heater is.
3. The wrong fuel. Biodiesel, HVO and high-ethanol petrol are approved on some models only.
4. Skipping maintenance. An unserviced heater is more likely to fail on the first cold morning.
5. DIY wiring and fuel connections. They risk leaks, faults and approval problems, and void the installation warranty.

Terms such as coolant circuit, heater matrix or glow plug are explained in our dictionary of automotive terms and the glossary, and more practical guides are in the advice section.