As a family, we frequently face weight and space constraints when going away on tour.

We also sometimes like to use basic campsites that don’t have full washing and shower facilities, because this maximises our choice of location.

It’s essential for us to have a fast, reliable water heater in our motorhome for these trips, so when Whale offered me a trial of its space-saving, lightweight Expanse water heater, I jumped at the opportunity to give it a thorough test.

What is it?

The Whale Expanse underfloor water heater is the first of its kind in the leisure-vehicle industry.

It is a dual-fuel (gas and/or electric) water heater, which promises to provide hot water without compromising on space.

Some ’vans have them fitted as standard, but it’s also possible to buy one as a standalone kit.

Retrofitting is a fairly straightforward process, but do be aware that it has to be undertaken by a qualified gas engineer.


The Expanse is mounted externally, underneath the vehicle, and it freed up 90% of the space taken up by our conventional inboard Truma heater.

With space at a premium in any motorhome, this provided valuable additional storage, allowing more room to take the kids’ paraphernalia with us, from footballs to buckets and spades.

A compact external height of only 262mm means that it sits comfortably next to the chassis frame.

This offers protection for the heater and should help it to avoid contact with the ground, a risk with anything mounted beneath your motorhome.

The outer casing is made from polypropylene, which is a lightweight and durable material that should enable the unit to cope with corrosive road salt and extremes in weather, along with preventing water ingress.

In addition, the thick insulation that surrounds the tank protects it from low temperatures.

Easy to use

In our ’van, the standard switch panel sits neatly under the seat in the dining area.

From here it is possible to control the fuel source – be it gas, electricity or both (for faster water heating).

There are two electric settings: low (750W/3.3A) and high (1500W/6.5A).

At some sites, particularly in mainland Europe, the electrical supply can be 6A or lower – using the low setting will reduce the risk of tripping the site’s hook-up.

For sub-zero conditions, there is a frost-protection switch, which will heat the water to avoid it dropping below 5ºC, preventing it from freezing.

However, it doesn’t stop water freezing in the supply pipes, so do bear this in mind if you are touring in extreme temperatures.

Draining down the system is straightforward: turn off the pump, open the hot-water tap until it runs dry, then rotate the yellow drain-valve handle into the drain-down position – the tank will simply drain out underneath the vehicle.

A further advantage of the Whale Expanse heater is that, with it installed underneath the ’van, there is no need to have large ventilation holes cut into the sidewalls of your motorhome, because the waste gases simply vent from underneath your unit.

Weight savings

Whenever you install any new kit, it’s always important to adhere to your motorhome’s Maximum Technically Permissible Laden Mass (MTPLM) or Maximum Authorised Mass (MAM) – this is your ’van’s legal maximum weight when fully laden.

Having said that, the Whale Expanse weighs only 4.5kg, compared with up to 7.2kg for a conventional heater.

This represents a substantial weight saving, allowing more room on board for your luxury items.

Being mounted under the vehicle, it also lowers the centre of gravity for more stablility on the road – it’s a win-win!

The eight-litre capacity of the Whale Expanse falls short of some other heaters on the market, however, which are typically 10 litres.

This issue is compensated for, to some extent, by a superior reheat performance through the system’s fully submerged heat exchanger and burner assembly.

Heating times

The maximum hot-water temperature achievable is 70°C, which is similar to other products on the market.

What is unique about this particular heater is that it has exceptionally quick reheat times.

On the highest setting it takes only 11 minutes to heat up for one shower, and around 20 minutes for two.

These are impressive times when you have a family of four to clean!

Long-term test

We’ve had our Expanse in situ for more than two years now, and have thoroughly tested it at sites with little or no facilities, such the New Forest and the temporary Caravan & Motorhome Club site at Birmingham’s NEC.

It has performed well both in the heat of a Spanish summer and the chilly temperatures of a Scottish winter.

It is a very neat, compact and reliable unit, and there have been no issues with the water temperature or the heat-up times, even after several showers in quick succession.

We’ve also been grateful for the additional space and overall weight saving that the unit gave us when we made the switch – surely something that all motorhome owners can appreciate.