Theo Stocker turns up the heat with a test of one of the new generation diesel heaters - the Eberspacher S2 D2L

Theo Stocker tests one of the new generation diesel heaters – the Eberspacher S2 D2L

Onboard heating is often the deciding factor when considering sailing early in the season, particularly if, like me, you sail with someone who doesn’t warm up easily once cold.

Away from shorepower, diesel heating is the only viable option. Eberspacher has just updated its Airtronic diesel heater range and they provided one of the first units in the country of the S2 D2L, which replaces the D2, for installation into our Sadler 29 for this test.

Innovations include a brushless fan motor to give quieter, more efficient heating and stepless variable speed; a fuel pump using spring-loaded valves to reduce the ticking noise; CAN bus switching via the new Easy Start Pro thermostatic controller to allow networking of more than one heater, and an easier user interface.

I was keen to see if these updates really did make the system quieter and more efficient.

The Eberspacher S2 D2L in use 

With the diesel forced air heater system fully connected, a long press on the Easy Start Pro controller’s single large button, the heater came on for a preset 30 minutes at 22oC.

The basic menu then gave options to change the default running time to anywhere between 10 and 720 minutes and an ‘infinity’ option, as well as options to change the default temperature, or to switch the heater off.

As the heater powered up and boosted to maximum output, it drew about 2.5A, warming the boat rapidly.

Easy Start Pro controller

The Easy Start Pro controller is easy to use once you get to grips with the menu system

In terms of fuel consumption, the  manufacturer claims the heater will use between 0.1L and 0.28L of diesel per hour, though we couldn’t easily measure this.

We closed the hatch and settled in, feeling warm and cosy.

Continues below…


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With the boat up to temperature, the rate of airflow slowed and the power draw dropped to 0.5-0.6A.

With a slower flow of air, there was very little noise, so the red LED circle around the control unit button and the gentle flow of warm air were the only clues that it was still on.

Delving deeper into the Easy Start Pro’s menus, we found options for cool air ventilation, seven-day timer programming, maintenance and basic diagnostic fault codes.

The idea of setting the heating to come on for an hour a day in winter, or on a Friday night before arrival on the boat, was appealing, though you need to be able to keep your batteries topped up
and switched on if you do.

If you buy the GSM module, you can switch the heating on via a phone app.


As performance and longevity of the heater depend on correct installation, I was glad this was done by a professional.

In operation, the system was unobtrusive once up to temperature.

Starting the system with a single button press was simple.

Beyond this, as with most menu systems, it took me a couple of attempts to work out what clicks and twists did what, but it was soon clear (instructions on a sticker would be helpful).

A woman sitting down below on a Sadler 29 reading

There was ice on deck in the morning, but this little heater made the boat very cosy. Credit: Theo Stocker

The heat was delivered quickly and at a steady temperature without sudden changes.

Sitting in the saloon we could not hear any ticking from the pump, which was apparent on boats with the older version of this system fitted.

The heater drew half an amp once up to temperature, which is 0.25-0.5A less than the power draw of the lowest two speeds of its predecessor.

The efficiency gains are small, but over several hours make a significant difference to battery charge.

Specifications of the Eberspacher S2 D2L


Kit, installation, labour and VAT £2,290

KIT INCLUDES: Airtronic S2 D2L heater, ducting, vents, wiring loom, fuel line and pump, Easy Start Pro control unit


Buy the Easy Start Pro controller from Amazon (UK)

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