It’s sometimes crazy: you want to heat a travel vehicle (a relatively large one, over 16 cubic meters of interior) and get different answers on the right heater sizing at every turn. Whether 2kW or 4kW – opinions truly divide sometimes.
We ourselves have been preaching for years: “Install the small one, it’s perfectly enough“.
In forums, on the other hand, you often read: “Buy the big one, it costs only 20 euros more, and you get double the output“. All in all, all we can say is: that is the completely wrong approach.
2 kW or 4 kW Auxiliary Heater: Ask Yourself These 3 Questions
2kW and 4kW are THE two standard sizes for auxiliary heaters in camper build-outs. The following questions help you clarify which one is really the right one for you.
How Big Is My Vehicle
This question is answered quickly: from about 16 cubic meters of volume you might think about more than 2kW.
The volume of built-in cabinets, seat benches, refrigerator etc. is not counted. If you come to more than 16 cubic meters, that still does not mean you definitely need the 4kW heater.
How Well Is My Vehicle Insulated
Are the walls of your cabin insulated 6cm thick anyway? Then even with a large room volume the 2kW heater may still be enough, because with such good insulation hardly any heat is lost.
If, however, there is only 19mm of Armaflex in a 7m Ducato, with no partition from the large, open windshield, then 2kW probably won’t quite be enough anymore.
To really settle this, the big question at the end is:
Where Am I Actually Going, and in Which Season?
Now it gets critical: with 2kW, a very well insulated vehicle can be heated without problems even below 0 degrees. From -15°C, though, you would rather have 4kW available.
A poorly insulated vehicle at 0 degrees with 2kW – no chance. There the 4kW heater definitely makes sense.
That means: if I spend the winter in Morocco with 6m of outer wall and mediocre insulation, 2kW is perfectly enough. If I take the same vehicle for a winter in Canada, it can get as cold as -40 °C and the big heater definitely makes sense.
The question that decides everything in the end, and which you have to assess realistically yourself: how wide is the range I have to cover?
Will I spend a notable number of travel days in really low temperatures, or do I only go on summer vacations anyway? How sensitive to cold am I, actually?
And: will I stay in Europe, or am I planning a long-distance trip where I spend a lot of time away from civilization and travel year-round? Besides heating output, this also has to do with redundancy – we’ll get to that shortly.
Also Keep in Mind
More heating output means more fuel consumption. With the big heater you may have to leave a window open in mild temperatures so it doesn’t get too warm inside – not a good idea for cost, the environment or your travel budget, to heat fuel out of the window.
The big heater is also quite a bit larger and weighs almost twice as much. With limited space and payload capacity, that is a not entirely insignificant difference.
So Who Really Needs 4kW
Large vehicles, especially if they are only weakly insulated or insulated with moderately good material. Here you could in theory install 4kW right away – but only if you hardly heat in the shoulder season. That is because the 4kW heater cannot be turned down as low. At mild temperatures, an unwanted sauna quickly develops in the vehicle.
If you believe the heating season starts in (European) November anyway and you only switch the heater on when temperatures are in the single digits – no problem.
If, on the other hand, you are sensitive to the cold and start heating at 15°C outside temperature, a 4kW heater is bad advice for you. It will always be either too warm or too cold.
A good example of a “4kW candidate” among smaller vehicles would be a barely insulated van for a trip to Siberia.
The All-in-One Solution
What should you do if you feel caught between all the stools: you have a relatively large room volume, sufficient insulation and are on the road in temperate regions most of the time – but you would also like to see the northern lights sometime without freezing!?
So if you (at least now and then) need the full heating output, or are planning a long-distance trip, our TWIN kit is the perfect all-in-one solution. It consists of two individual 2 kW heaters.
We’ll explain in a moment why that is supposed to be an advantage when you could just as well install a much cheaper 4kW heater. First, though, let’s look at why it is bad at all to install a single 4kW heater when you don’t really need it.
Why Not Just 4kW for Only a Little More Money
True, one heater costs less than two. But if my goal is potentially to travel all continents in every season, I have a big problem: in many cases I run my auxiliary heater in the lower part-load range, because, let’s be honest, extreme conditions are quite rare after all.
So the heater never gets properly hot and over time soots up as a result. Consequently the heating output drops until the coking has progressed so far that the heater finally no longer starts. In our experience, such things happen exactly when extreme conditions actually occur and you urgently depend on the heater.
What Does the Small Heater Do Better
In the heat-up phase, every heater first runs at full output until the desired target temperature is reached. With the same room volume this is of course somewhat faster with more heating output – say 15 min at 4kW and 30 at 2kW.
For the service life of the heater, the longer time is an advantage. In 15 min a heater is at operating temperature for just 10 min and has not yet been able to burn itself clean properly. The small heater, on the other hand, then runs 25 min at the highest level and so was able to clear its combustion chamber of soot deposits.
In addition, consider the following: when a 4kW heater runs at 1kW, it needs just as big a fire (i.e. an identical amount of fuel) as a small heater.
The decisive difference, however, is that a 4 kW heater has a combustion chamber twice as large and a heat exchanger with (in terms of surface) twice the area. The combustion chamber temperatures of the 4 kW heater can’t always be optimal in the low-load range, because here “the bigger house has to be heated” with the same energy.
So if you can expect a lot of low load for a 4kW heater, you should go straight for the 2kW heater or the Twin kit.
What Are the Advantages of the Twin Kit
What at first glance sounds like a bad joke from the auxiliary heater mafia is in reality the optimum for traveling with medium-sized to large vehicles in all climatic conditions.
Instead of using one 4kW heater, the kit combines two individual 2kW heaters into one overall system without coupling them electrically. That means:
Full 4kW – but Only When You Really Need It
With the Twin kit you can have the full 4 kW of heating output.
In the shoulder season, however, you can heat with a single, easily controllable 2 kW heater – without freezing, but also without opening a sauna and without the heater coking up.
Full Redundancy
With two completely independent heaters, you enjoy full redundancy of your heating system.
For trips to regions with extreme winter conditions (Canada, Lapland etc.) or far from civilization, redundancy is essential. You simply can’t afford to be stuck without heating for a few nights at -45°C.
Likewise, you can’t get spare parts anywhere in the deepest outback. Depending on the weather conditions, it is vital for (survival and) life that the heater works!
That two independent heaters break down at the same time – highly unlikely.
Two Heaters, Hardly Any More Space Required
With the TWIN double installation flange two individual heaters can be integrated in the tightest space. They share a single air system. There is no need for mechanical parts such as air flow valves or the like.
All the Advantages of the Individual Heaters Retained
Of course both heaters have an integrated altitude kit for fuel injection that automatically adapts to air pressure. This means operation is no problem even at the highest altitudes.
Optionally, the kit can be given full sound damping, i.e. suitable silencers are available for both the intake and the warm air side. This gives the system a certain length. In large expedition vehicles in particular, with partial double floors etc., it can usually be planned in without problems and accompany the owner across all continents and through all seasons.
Twin Kit with Hot Water Boiler
Like the individual heaters, the Twin kit can also be operated with a hot water boiler as a Hot Shower Kit. This incidentally allows you more than just a hot shower. With the combiBOIL hot water boiler you can also set up engine preheating for gentle starting in winter, underfloor heating or a towel dryer – and not only while the auxiliary heater is running.
You can find out more right here, in the shop
How Is the Temperature Controlled with the Twin Kit
Suppose that at current temperatures about 3kW are needed to maintain a comfortable room temperature. Which heater regulates that? Should both heaters run in temperature mode at the same time?
Getting the two heaters to settle on a value to hold is difficult, and there is a much simpler way:
One of the two heaters is given a fixed output. It covers the basic heat demand and sets the base temperature. The second heater takes over the additional demand and is responsible for temperature control.
Conclusion on Heater Sizing and the Twin Kit
From our point of view, that is, from technical background knowledge of the heaters and from many years of travel experience of the tigerexped team, the Twin kit is the only sensible choice when a relatively large vehicle is heading out on long trips.
It provides
- safety through full redundancy,
- comfortable temperatures, whether the outside temperatures are mild or extreme
- protection of the environment and travel budget through appropriate fuel consumption
- a long service life of the heaters through operation with burn-free (self-cleaning) times.
Do you think the TWIN kit is a good idea for your vehicle? Talk about it with friends and like-minded people by sharing the article with them!
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