Propane or butane? Which gas for a motorhome or caravan

Bottled gas is stored as a liquid. To reach your hob, heater or fridge it has to boil off into a gas inside the cylinder, and boiling takes heat from the air around it. Butane boils at around freezing, so as the temperature drops towards 0C it simply stops producing gas. Propane boils at a far lower temperature and carries on gassing off down to about minus 40C, the Camping and Caravanning Club says.

That is the whole story, and it explains the night a winter tourer least wants. It will be the coldest night of the trip, somewhere after midnight, the heater will cough and stop, and the cylinder you shake in the locker will still slosh. There is gas in there. It just can't get out.

The Camping and Caravanning Club puts the line at 4C: if temperatures are expected to reach 4C or lower, use propane. The Caravan and Motorhome Club says the same thing in plainer terms. For winter touring, switch to propane.

In practice that means from some time in autumn until spring for most of Britain, and any night on high ground or in the far north. A clear sky in October can take a valley below freezing even after a mild day. If you tour all year, propane all year is the simple answer: it works in every season, and you only lose a little efficiency in summer.

Calor, the largest bottled gas supplier in the UK, sells butane in blue cylinders and propane in red, the Camping and Caravanning Club notes. Other suppliers use their own colours and labels, so read the label rather than trusting the colour alone, especially on a refill or an exchange cylinder from a supplier you haven't used before.

Before you swap from one gas to the other, check that the regulator and the connection on your van suit the cylinder you are fitting. If you are not sure what you have, ask a qualified gas engineer: anything beyond changing a cylinder is a job for a professional.

In warm weather, yes. Butane is a little more efficient than propane, the Caravan and Motorhome Club says, so it works out cheaper for the summer. If you only tour from late spring to early autumn and never sleep high, a blue cylinder does the job well. The moment your trips stretch into the cold months, the small saving stops being worth the risk of a silent heater.

More than you think. Heaters use quite a lot of gas and battery power, the Caravan and Motorhome Club warns, because the fans, pumps and control systems run on 12 volts. Before a winter trip away from hook-up, make sure you have enough of both. A spare full cylinder in the locker is cheap insurance.

Hook-up changes the sums. On a site with mains power you can run a small electric heater and save the gas for cooking and the fridge. The Caravan and Motorhome Club suggests a small, thermostatically controlled fan heater on hook-up, around 1kW, for a quick boost first thing in the morning. The Camping and Caravanning Club recommends looking for a 16A hook-up in winter, and points out that a 2kW heater uses just over half of that, so add up what else is running before you switch on the kettle.

Cold also slows down the chemistry in a battery and reduces its capacity, the Camping and Caravanning Club says. Lithium (LiFePO4) batteries can be drained further and weigh about half as much for the same capacity, but they cannot be charged below zero, so a lithium battery fitted somewhere cold may need one with its own internal heater. If you plan to stay a few nights without hook-up in winter, start fully charged and think about a second battery or a generator.

Anything that burns gas can make carbon monoxide if it is faulty, badly installed or poorly maintained, the NHS says, and gas heaters and cookers are on its list. Carbon monoxide has no colour and no smell, so you can't tell it is there.

The signs the NHS lists are a headache, dizziness, feeling or being sick, weakness, tiredness and confusion, chest and muscle pain and shortness of breath. They may come and go, and get better when you go outside. In a van, where everyone sleeps a few feet from the heater, that pattern matters: a headache that lifts on a morning walk and returns in the evening is worth taking seriously.

The NHS advice translates straight to a van. Fit a carbon monoxide alarm that makes a loud sound. Have heating and cooking appliances properly installed and serviced regularly by a qualified, registered engineer. Keep the space ventilated. Never use a barbecue or a camping stove inside, and never run an engine or a generator in an enclosed space. If you think someone has carbon monoxide poisoning, stop using the appliance, get outside and get medical advice: call NHS 111, or 999 if someone is struggling to breathe, confused or unconscious.

Winter is when the vents get blocked, the doors stay shut and the heater runs longest. Check the alarm's battery at the start of the cold season, the same day you swap to propane.

Put the advice together and a simple plan falls out. On the coldest nights, choose a site with hook-up, ideally 16A, and let mains power carry the heating while gas does the cooking. On nights off hook-up, run on propane, start with a full battery, carry a spare cylinder and keep the vents clear. Swap back to butane in late spring if you want the small summer saving, or stay on propane all year and stop thinking about it.

• Propane in the locker, and a spare.
• The right regulator for the gas, or a universal one.
• Leisure battery fully charged before you leave.
• A site with hook-up for the coldest nights, ideally 16A. The Winter Campsite Index shows which winter sites have it.
• A plan for water and waste in a frost: see winterising a motorhome or caravan.

None of it is complicated. It is the kind of thing you do once, properly, at the start of the cold season, and then stop thinking about.