Nobody tells you how cold a steel or fibreglass hull gets when you sit still on a canal in October. On the move you generate your own warmth, the sun is usually out, and the heater feels like a luxury. Tie up under the plane trees on the Canal du Midi as the first proper cold front comes through, and the boat turns into a fridge by nine in the evening. We spent our first French autumn aboard pretending we did not need heat. By the second we had a proper system, and it changed the whole experience of being on the water out of season.
This is what I wish someone had told me before I spent the money.
The three types, and what they actually do
There are three serious options for keeping a boat warm in France, and they suit different boats and different wallets.
Diesel air heaters blow hot air through ducting from a small combustion unit. They are the most common choice on production cruisers and the easiest to retrofit. A Webasto Air Top 2000, a 2 kilowatt unit suited to boats up to around 35 feet, is the benchmark. Installed kits in the UK run from roughly 1,900 pounds upward in 2025 depending on ducting and labour, and the unit sips between 0.12 and 0.24 litres of diesel per hour. On a canal boat with a big tank that is almost nothing.
Diesel hydronic (or wet) heaters run hot water through a small radiator circuit and often heat your domestic water and engine too. They are quieter at the cabin end because the burner lives in the engine bay, but they cost more and the plumbing is a bigger job. This is the system I would fit on a steel barge meant for living aboard through winter.
Solid fuel stoves, the little cast iron jobs you see on Dutch barges and narrowboats, are wonderful and have no electrical draw at all. The downsides are the chimney, the mess, and the fact that you cannot leave them unattended overnight. On a canal boat that never moves much they make real sense. On a sailing boat they are usually impractical.
Diesel air is the sensible default for most visitors
If you are bringing a coastal cruiser into the canals for a season, or splitting your time between the French canals as a beginner and the coast, a diesel air heater is almost always the right call. It is compact, it runs off the fuel you already carry, and it works equally well at anchor in a Brittany creek in April or tied to a canal bollard in November.
The two big names are Webasto and Eberspacher, with Wallas a strong third on sailing boats. Note that the long serving Wallas 30DT, a quiet 3 kilowatt unit good for boats up to 12 metres, has been discontinued and replaced by the 30GB, which keeps the same external dimensions and controls so it drops into the same hole. If you buy second hand and someone offers you a 30DT, that is why it looks dated.
A word on cheap Chinese diesel heaters: they are everywhere online for under 200 pounds and plenty of canal cruisers run them happily. They are not marine rated, the build quality is a lottery, and your insurer may take a dim view of one feeding a sealed cabin. I would only fit one with a proper marine flue, a carbon monoxide alarm, and eyes open about the risk.
Sizing it: do not go too big
The instinct is to buy the biggest heater you can afford. Resist it. An oversized diesel air heater short cycles, sooting up its burner and never running long enough to come up to clean temperature. That is the single most common reason these units fail. For a typical 10 to 12 metre boat a 2 kilowatt unit is plenty for the canals, where you are usually heating one cabin in the evening rather than fighting an open cockpit at sea.
Work out the volume of the space you actually heat, allow for poor insulation on an older hull, and size for that. If you genuinely live aboard through a continental winter on the Canal de Bourgogne, where it gets properly cold inland, then step up, but most seasonal cruisers are over heated by 2 kilowatts on the canals.
Fuel, power and the things that bite you
Two practical points that the brochures gloss over.
First, diesel air heaters draw a surprising amount of electricity on start up, when the glow plug fires, often 8 to 10 amps for a couple of minutes. If you are off grid and your batteries are tired, repeated starts will flatten them. Plan your canal stops so you can top up shore power where it is available, or carry enough battery and charging to cope. Many canal halts have power, but the cheap free moorings do not, and that is exactly where you want heat.
Second, diesel quality matters. The gunge that collects in the bottom of a tank you have not used much will block the tiny metering pump in a diesel heater faster than it bothers the engine. Fit a separate small standpipe or a good pre filter, and run the heater regularly even in summer so it does not seize. Sorting out diesel, water and pumpout on a French canal trip is its own subject, and worth reading up on, because the diesel, water and pumpout on French waterways network is patchier than you expect.
What it costs to run, and is it worth it
Take a Webasto 2000 running an average evening, say five hours, at a middling output. Call it 0.7 to 1 litre of diesel a night. At French marine diesel prices that is small change, well under two euros for a warm, dry boat. Over a six week autumn cruise the running cost is trivial next to the marina fees.
The real value is what it lets you do. With heat aboard you can cruise the shoulder seasons, April and May, October and November, when the canals are empty, the locks are quiet, and the whole country is at its best on the water. If you are thinking about wintering a boat on the French canals, a reliable heater is not optional, it is the line between a damp, miserable lay up and a boat you actually want to spend time on.
Heat is only half the job: damp
A heater that warms the air without dealing with moisture just moves the problem around. Steel hulls in particular sweat, and a fibreglass boat shut up tight will grow black mould in the lockers if you only ever heat the saloon. The trick is gentle background heat plus airflow. A diesel air heater helps here because the warm air it circulates also dries, but you still need to crack a vent and keep air moving through the boat, even on a cold night. I run a small low draw fan to push warm air into the forward cabin, which otherwise stays cold and damp while the saloon roasts. Open the lockers when the heater is on so the dry air gets behind the lining where the mould actually starts.
My honest recommendation
For a visitor bringing a normal cruiser into France: fit a 2 kilowatt diesel air heater from Webasto or Eberspacher, add a carbon monoxide alarm whatever you buy, and budget for professional installation if the ducting run is awkward. Keep it serviced and run it monthly.
If you are committing to a barge and a continental winter inland, spend more on a hydronic system or add a small solid fuel stove for the deep cold and the simple pleasure of a real flame. Either way, the heater you fit before your first autumn is the kit that turns a fair weather toy into a boat you can use most of the year.
