Campervan hot water: calorifier vs on-demand vs none — what each costs in weight and space
· 8 min read
The heater is the light part. A calorifier costs 18 kg and 0.12 m² of floor, a combi 25 kg and 0.27 m² (12 kg net, because it replaces the air heater), an on-demand LPG unit 5 kg on a wall, and none 0 kg. The habit each one buys — a daily on-board shower — costs 78 kg of fresh water on a three-day trip for two and a grey tank twice the size. Decide the shower first; the heater follows. That is the answer. Below is the table behind it, computed from the planner’s catalog items and the water tool’s litre figures, with every assumption written down.
The tank-size post and the autonomy post cover volume — how many days a tank lasts. Neither says how the water gets hot, and hot water is the decision that quietly sets the volume: nobody plans a 25 L/person/day budget until there is a shower to spend it on. This post is that missing step.
The assumptions
- Calorifier: the catalog’s water heater — a 35 cm cylinder, 8 kg dry, 300 W element, €260. The catalog does not carry a litre figure, so I compute with 10 L, the common engine-plus-230 V size that fits that shell.
- Combi: the catalog’s combi heater (air + water) — 0.54 × 0.35 × 0.50 m, 15 kg dry, 40 W fan draw, €2,100, and again 10 L of stored water. It replaces the diesel air heater (0.31 × 0.145 × 0.12 m, 3 kg, €480), so the net figures below subtract that.
- On-demand LPG heater: not in the catalog. Figures are the typical 5 L/min portable-class unit, labelled as such: about 0.30 × 0.12 × 0.44 m on a wall, 5 kg, €150–300, flue to outside, fed from the gas locker.
- None: kettle on the hob, bowl, 20 L shower bag or pump sprayer — the catalog’s jerry can (20 L, 21 kg full) stands in for the bag if you carry one.
- Water: 1 kg per litre; one shower = 11 L (the water tool’s
SHOWER_LITERS); usage profiles 12 L/person/day without an on-board shower and 25 with one (the tool’s normal and comfort profiles); 85 % of fresh ends in grey. - Heat: 4.186 kJ per litre-kelvin. Stored water at 60 °C, cold at 10 °C, shower at 38 °C. Propane 46 MJ/kg at 80 % burner efficiency; €3/kg.
Table 1: the four options, per unit
| Option | Dry | Full | Footprint | Volume | Hot water on tap | Energy per 11 L shower | Catalog cost |
|---|---|---|---|---|---|---|---|
| Calorifier 10 L, engine + 230 V | 8 kg | 18 kg | Ø 0.35 m, 0.12 m² floor | 0.043 m³ | 6.2 L of 60 °C per fill ≈ 1.5 showers; reheat 0.47 kWh | free while driving; 93 min on 300 W = 39 Ah | €260 |
| Combi air + water 10 L (LPG or diesel) | 15 kg (net +12) | 25 kg (net +22) | 0.54 × 0.50 m, 0.27 m² (net +0.23) | 0.095 m³ | same 1.5 showers; reheat in 20–30 min on gas | ≈ 45 g propane per reheat | €2,100 (net +€1,620 over an air heater) |
| On-demand LPG 5 L/min (typical, not catalog) | ≈ 5 kg | ≈ 5 kg | 0.30 × 0.12 m on a wall, 0.036 m² | 0.016 m³ | continuous at 5 L/min, 28 K rise | ≈ 35 g propane ≈ €0.10 | €150–300 |
| None (kettle + bag) | 0 | 0 (21 kg if a 20 L bag is full) | 0 | 0 | 1.5 L per kettle; a bag warms in the sun | ≈ 12 g propane per 1.5 L kettle | €20–40 |
Table 2: what the shower does to the tank
Two people, three days between taps, from the water tool’s profiles. This is the number the heater comparison hides.
| Habit | Litres per day | Fresh for 3 days | Grey to match (85 %) | Catalog tanks that cover it | Water on board, day 1 |
|---|---|---|---|---|---|
| No on-board shower (kettle, bowl) | 24 L | 72 L | 61 L | arch tank 90 L (95 kg full) or 2 × 35 L (76 kg) | 72–90 kg |
| Daily on-board shower each | 50 L | 150 L | 128 L | 125 L + 35 L (168 kg full) | 150–160 kg |
| Difference | +26 L | +78 L | +67 L | one more tank, one more grey | ≈ +78 kg |
How to read it
- Weight: the tank, not the heater. The heaviest heater option (combi, 25 kg full) is a third of what the shower habit adds in water (78 kg). If your reason for hot water is dishes and a wash, take the kettle: zero kilograms, zero litres, and the tank stays at 90 L. If the reason is a daily shower, budget the 78 kg before you compare heaters — and put it over the axle, which is what the tank post is about.
- Space: the combi is the only one that eats floor. 0.27 m² is the area of a small kitchen cupboard; it earns it back only because it also heats the air, so count it against the air heater’s 0.04 m² and the bathroom’s footprint from the toilet-and-shower post, not against nothing. The calorifier is a 35 cm drum under a seat or behind the wheel arch; the on-demand unit is a wall box in the shower cubicle itself.
- Energy: a calorifier is an engine accessory. 0.47 kWh per reheat is 39 Ah from a 12 V battery — a fifth of a 200 Ah bank for one and a half showers. Plumb it to the engine coolant (free after 20 minutes of driving) and use the element on hook-up only. The on-demand heater sidesteps the battery entirely: 35 g of gas per shower, an 11 kg bottle lasts 300 showers.
- The combi’s honest price is €1,620 and 12 kg. You were buying an air heater anyway; the hot-water half of a combi costs the difference. Against a calorifier (€260, 18 kg full) that is expensive; against a calorifier plus a diesel heater it buys one install, one flue and one fuel — the heater-sizing post says what kW the air half needs.
- Gas heaters bring the locker with them. An on-demand LPG unit or a gas combi means a sealed locker with a drop-out vent and a regulator, whatever you had planned for cooking. The gas-locker post has the rules; the point here is that “5 kg on a wall” is 5 kg plus a 26 kg bottle and a box.
- Winter halves the calorifier. At 5 °C cold water the shower is 60 % hot instead of 56 % — small — but the 10 L drum loses heat overnight and starts the day cold, and an engine calorifier needs the engine to have run. The on-demand unit is the winter option; the kettle is the always option.
Which one, then
Weekender, no shower: none. Dishes from a kettle, a bag shower at the beach, 90 L tank, done. Full-timer with a cubicle, driving most days: calorifier on the engine — 18 kg, €260, hot water waiting when you park. Full-timer who sits still for days and showers daily: on-demand LPG — no stored heat to lose, no battery drain, 5 kg — and the 150 L of tank that goes with the habit. Combi: when you want one appliance to do both and the €1,620 buys you the second install you would otherwise do yourself. Whether the cubicle is worth its floor at all is the shower-or-not post.
Before you buy the tank
Drop the heater you are leaning toward into the planner next to the tank it implies — the catalog carries the water heater, the combi and all three tank sizes with their full weights — and read the rear-axle figure. Hot water is the second-heaviest decision in the build after the bed, and it is made in the plumbing aisle where nobody weighs anything.
FAQ
Do you need a water heater in a van conversion?
Only if you shower on board. Dishes and a wash come out of a kettle on the hob for zero kilograms and zero litres of extra tank. A daily on-board shower is 11 litres a time and moves two people from a 12 to a 25 litre-per-person-day budget — that is 78 kg more fresh water for a three-day trip, before the heater itself (5–25 kg) is counted.
How much does a campervan calorifier weigh?
A 10-litre engine/230 V calorifier of the size in the planner's catalog is about 8 kg dry and 18 kg full, in a 35 cm cylinder (0.12 m² of floor). A combi air-and-water heater is 15 kg dry, 25 kg with its 10 litres, and takes 0.54 × 0.50 m of floor — but it replaces the 3 kg air heater, so the net cost of hot water is 12 kg and 0.23 m².
Is an on-demand LPG water heater lighter than a calorifier?
Yes — about 5 kg on a wall with no stored water, against 18–25 kg on the floor. It burns roughly 35 g of propane per 11-litre shower and needs a flue and a locker-compliant gas feed. What it does not save is water: it makes endless showers possible, and the tank pays for that.
How many showers does a 10-litre calorifier give?
About one and a half. A shower at 38 °C from 60 °C stored water and 10 °C cold is 56 % hot, so an 11-litre shower draws 6.2 litres from the tank. Reheating 10 litres by 40 K is 0.47 kWh — 20–30 minutes of engine or gas, or 93 minutes on the 300 W element, which is 39 Ah at 12 V and the reason calorifiers are heated by the engine, not the battery.
