Boat Heating

After looking in the gas locker I think that Speedwell originally had a gas fired heater, but that’s long since gone and when we bought her she didn’t have any cabin heating. We live on the boat for extended periods and take her to some out of the way places so a decent heating system makes life much more pleasant.

During the 2009/10 refit we had a Webasto Thermo 90 ST system fitted. This is a diesel fired system that heats the boat through hot water piped to radiators (rather than the more common blown air system). Although more expensive than a blown air system the water based system gave a neater installation and is, we believe, better in use.


The main heater unit is fitted in our lazarette, with a diesel feed from the reserve fuel tank. We had a wire cage made up to fit over the heater to give it some protection from the rough and tumble of life in a locker. The on/off switch is on a bulkhead next to the bunk in the owner’s cabin so we can reach out and turn the heating on from under the duvet.

Relatively small bore pipes are used to run water to and from the heater, these were much less disruptive to route through the boat than large bore hot air ducting. The heater has its own closed circuit water system, with a header/expansion tank in aft deck rope locker.

The cabins are heated by small radiators, each of which has a fan that blows air through the heater matrix. Each fan is controlled by a thermostat and on/off switch in its cabin so we have independent control of the temperature in each cabin (with the exception of the forward heads compartment which is controlled by the thermostat in the forward cabin).

We’ve also had a convection radiator fitted across the bottom of the hanging locker in the forward heads to give us a heated wet locker, which is great for drying out wet gear on a rainy day.

An option that we didn’t take up was to include domestic water heating. This would have required a new calorifier with twin coils (one taking hot water from the engine and the other taking hot water from the heater). Although domestic hot water from the heater would be a nice extra we didn’t think that the additional expense was worth it during the re-fit, we may re-consider this later.


After a season in the variable Scottish summer climate we’ve been pleased with the performance of our heating system.

From initial turn on it takes several minutes to get the circulating water up to temperature, at which point the fans turn on, so it is a little slower to get going than a blown air system. Once it’s running we get plenty of heat in each cabin, even in the forward heads compartment which is at the opposite end of the boat to the heater.

With a separate thermostat in each cabin we’ve got much better control of temperature through the boat than we would have with a blown air system (on our previous boat we’d find that the aft cabins got too hot and the forward cabin never got enough heat). If we’re not using the forward cabin we can turn the heat off in there.

The heater fan for the forward heads is controlled by the thermostat in the forward cabin, and there’s also a convection heater in the heads locker, so that compartment does get hotter than the adjacent cabin. However we used the forward heads compartment as a shower and for drying gear so a little extra heat in there isn’t a problem.

There is some noise from the heater matrix fans but these are much quieter in operation than blown air heating systems that I’ve come across.

We don’t get any of the diesel smells than sometime afflict blown air systems.