In brief
Motorhome heating comes in three families: an LPG gas fired heater that warms the cabin air directly, a hydronic boiler that heats water and a separate loop of radiators or floor piping, and a diesel-fired heater that burns the vehicle’s own fuel to make hot air or hot water. Cooling is either engine-driven, run only while you drive, or driven from the mains, and that distinction is why an RV in a hot climate is often cooler in its cab than in its cabin.
Gas fired heater: cheap, simple, thirsty
A gas fired heater is the standard solution and works without any engine or mains: it takes air from the cabin, warms it and returns it, usually with a ducted or a blown-air layout. The cost is gas. A well-insulated European campervan at 0 degrees outside will burn roughly one to two kilos of LPG an hour while the heater runs, which empties a small bottle in a day. Budget for a second bottle and a spare. It also needs ventilation and a carbon monoxide alarm, and the return air must not be drawn from a sealed cupboard.
The boiler and hydronic heating
A boiler heats water, and the water heats the cabin through radiators or through piping embedded in the floor. It is slower to respond but far more comfortable, because it radiates rather than blows, and the floor loop keeps the whole cabin even at a low temperature. It is the system most commonly specified in European motorhomes and is usually plumbed into the same loop as the hot water. The catch is water: the boiler holds water, so it must be drained or antifreezed before a freeze, and an empty boiler fires on a dry system.
Diesel-fired heaters (air and water)
A diesel heater burns the vehicle’s own diesel to produce hot air or hot water, and is the reason a pickup camper or an expedition rig can sit in the snow with the engine off. It needs a fuel line, an exhaust for the combustion byproducts and a professional installation to be safe; a badly installed diesel heater is a carbon monoxide hazard, not a comfort feature. It is quieter than a generator and needs no LPG, and it is the preferred solution for anyone who sleeps in the vehicle every night in a cold climate.
Air conditioning: what actually works
Engine-driven air conditioning only works when the engine runs, which makes it useless on a static pitch. Mains-driven units run from a 120 or 230 volt supply and are what you use while parked. A generator or a large lithium bank plus an inverter can run one, but realistically you need the mains supply or a big generator. In a hot European climate the parks are often chosen for their shade first, and cross-ventilation plus two good vents beats any single air conditioner for comfort.