Start with heat loss, not heat output

A garden office is usually a small, lightly built box with far more exposed surface area per square metre than a house. Most of the heat you pay for disappears through the walls, roof and floor before it has done any useful work. So before you spend a penny on a heater, take a hard look at the fabric of the building.

If your cabin has insulation in the walls and roof (50mm is a minimum, 75–100mm is much better), an insulated floor, double-glazed windows and draught-proofed doors, you can heat it comfortably with modest output. If it's a single-skin shed with gaps around the door, even a 2kW heater will struggle on a frosty morning. Sorting the insulation first is the single cheapest thing you can do, and it can halve your running costs.

It also helps to know what kind of warmth you want. Do you want the whole room at a steady 19°C all day, or do you mainly want to feel warm while sitting at a desk? That distinction decides whether convection, radiant or solid-fuel heating suits you best.

Electric panel heaters: simple, steady and easy to control

Convector panel heaters are the default choice for most garden offices, and for good reason. They're cheap to buy, easy to wall-mount, silent enough for calls, and controllable with a thermostat and timer. Oil-filled radiators are a cousin of the panel heater: slower to warm up but they hold heat for a while after switching off, which suits cabins with decent insulation.

Sizing is straightforward. As a rough guide, allow around 100W per square metre for a well-insulated garden room and 150–200W per square metre for a poor one. A 6m² office might manage with 750W; a 12m² cabin that loses heat quickly may want 2kW.

Running costs follow the wattage. At an electricity price of roughly 25–30p per kWh, a 1.5kW heater running flat out costs about 38–45p an hour. In practice, a thermostatically controlled heater in an insulated room cycles on and off, so the average is often half that or less. Look for one with a 7-day timer so it's warm before you walk in, rather than being left on all night.

Infrared panels: warmth where you sit, almost instantly

Infrared panels work differently. Instead of heating the air, they radiate heat that warms surfaces, furniture and people directly. You feel the benefit within seconds of switching on, which makes them excellent for a garden office where you sit still in one place for long stretches.

They're slim, often frameless, and look far tidier than a bulky convector. You can mount them on a wall or the ceiling, ideally angled so they wash over your desk chair. Panel sizes typically range from 350W to 700W, and a single 600W panel costs roughly 15–18p an hour at current rates.

The catch is that infrared warms you, not the room. Step away from the beam and the effect fades. They're a poor choice if you want the whole cabin at a comfortable air temperature, or if you move around a lot, or if you have clients sitting in the cold spot. For a solo worker at a desk with a decent base temperature, they're a very efficient option. Many people pair a small oil-filled radiator on a low setting with an infrared panel overhead for the best of both worlds.

Small wood burners: character with a longer to-do list

A tiny wood burner is the most romantic option and, per kilowatt of heat, often the cheapest to run. Seasoned logs bought in bulk can work out at roughly 6–10p per kWh of heat, though kiln-dried logs in small carrier bags can cost as much as electricity.

The downsides are practical and regulatory:

• Installation is not a DIY job. A solid-fuel appliance needs a properly sized twin-wall insulated flue, clearance from combustible materials, a non-combustible hearth and a permanent ventilation opening.
• Building control approval is often required, and an installer registered with a competent person scheme can usually certify the work for you.
• Smoke control areas cover much of urban Britain. Inside one, you must use an exempt appliance and authorised smokeless fuel or dry wood.
• Insurance – tell your provider. Some policies exclude solid-fuel appliances in outbuildings altogether.
• Practicalities – you need dry log storage, somewhere safe to empty ash, and a carbon monoxide alarm regardless of what the regulations say.

You also need to accept that a wood burner takes 20–30 minutes to bring a cold cabin up to temperature, and it needs feeding. If you work in your garden office every day, the ritual is part of the pleasure. If you dip in for an hour at a time, it's a faff.

Running costs compared

• Electric panel heater, 1.5kW: roughly 38–45p per hour at full output, less when cycling on a thermostat.
• Infrared panel, 600W: roughly 15–18p per hour while switched on.
• Wood burner: roughly 6–10p per kWh for bulk seasoned logs, plus installation and maintenance.

Numbers only tell part of the story, though. An underpowered heater left running all day can cost more than a well-sized one used for two hours. And no heater can compensate for a leaking, uninsulated cabin.

Controls, safety and sensible habits

Whatever you choose, fit a thermostat and a timer rather than relying on manual switching. A programmable thermostat that drops to 12°C overnight and lifts to 19°C before you start work will save more than switching heater type ever will. Smart plugs and app-controlled thermostats are inexpensive and genuinely useful for a building you don't heat continuously.

Keep a background temperature of around 10–12°C during cold snaps to keep damp at bay, especially if you store paper, electronics or fabrics out there. Ventilation matters too: a sealed, well-heated cabin with no air movement will grow condensation on windows and cold corners. A trickle vent or a brief daily airing does more good than extra heat.

Finally, keep safety in mind. Don't drape anything over a panel heater, keep infrared panels clear of furniture and curtains, site wood burners on a proper hearth with a guard if children or dogs use the garden, and fit a carbon monoxide alarm in any cabin with a solid-fuel appliance. Get those details right and your garden office will be a comfortable place to work right through the winter.