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Start With Insulation, Not the Heater

Before you spend a penny on a heater, spend a thought on the fabric of the building. A small garden room is usually a timber-framed box with a lot of surface area, so heat escapes faster than in a house. If the walls and roof have only a token layer of insulation, even a generously sized heater will struggle on a frosty January morning and your energy bills will show it.

Aim for at least 50mm of rigid insulation board or mineral wool in the walls and roof, a solid insulated floor, and well-fitted double-glazed doors and windows. Draught-proof around doors, seal gaps where services enter, and line the ceiling. Once the room holds its heat, a modest 500W to 1kW heater will often do the job. Insulation is not glamorous, but it is the single biggest factor in how comfortable — and how cheap — your garden room feels.

Electric Panel Heaters

Electric panel heaters are the default choice for most garden rooms, and for good reason. They are slim, wall-mounted, inexpensive to buy and simple to install — usually just a fused spur or a plug on a suitable circuit. A 1kW panel will gently warm a well-insulated room of around 10 to 12 square metres, while 1.5kW suits a larger or less insulated space.

They work by convection: air passes over the element and rises, circulating warmth around the room. This makes them good for background heat you leave on for long stretches, especially with a built-in thermostat and timer. They are less impressive if you want instant warmth when you walk in. Running costs are straightforward: a 1kW heater uses one unit for every hour at full power, though a thermostat will cycle it on and off.

Infrared Heaters

Infrared heaters take a different approach. Instead of warming the air, they emit radiant heat that warms people and surfaces directly — a bit like sitting in the sun. That makes them ideal for a garden room used in short bursts: a studio for an hour, a home office for the morning, a hobby room on a winter afternoon.

Panels of 350W to 700W are often enough for a small room. Because they do not heat the air, the warmth is almost immediate and you need not leave them running. The trade-off is that they only warm what they see, so they work best when you are sitting or standing in the beam. They pair nicely with a panel heater: instant infrared warmth for the person, gentle background convection for the room.

Wood Burners

A small wood burner is the romantic option, and in the right room it is a delight. Crackling flames, a kettle on top, that particular smell of seasoned ash or birch — it turns a shed into a proper retreat.

A wood burner needs a properly installed flue and adequate ventilation, and in many parts of the UK you must be in a smoke control area, which means using a DEFRA-exempt stove and burning only dry, seasoned wood or approved fuel. Installation is a specialist job, and you should check the rules with your local authority and insurer first. A 4kW to 5kW stove is usually plenty for a small garden room; larger models will turn it into a sauna. Keep combustible materials well clear, fit a carbon monoxide alarm and a fire extinguisher, and have the flue swept annually. If your garden room is a lightweight timber structure, the heat output and clearances may simply rule it out.

Sizing, Controls and Running Costs

As a rough guide, allow about 60 to 80 watts of heating per cubic metre for a well-insulated garden room, and more like 100 watts if the insulation is basic. Measure the room's length, width and height, multiply, and then round up. Better still, choose a heater with a thermostat so you are not paying to overheat a space you only use occasionally.

A programmable thermostat, a simple timer or a smart plug lets you warm the room before you go out and switch it off when you leave. Frost protection is worth having if you store tools, paint or plants through the winter. Infrared panels generally run cheaper per hour than convection heaters in a draughty room, because they do not waste energy heating air that leaks away. Whatever you choose, keep an eye on the kWh figure rather than the wattage alone.

Safety and Practical Points

Safety is not an afterthought in a small garden structure. Fit a carbon monoxide alarm if you burn any fuel, and a smoke alarm regardless. Make sure electric heaters are on a circuit protected by an RCD, never run them from coiled extension leads, and keep them at least a metre from curtains, cushions and cardboard boxes.

Check the IP rating if the room is damp or you plan to use a heater near a door that opens to the garden — IP24 or better is sensible. Never use a patio heater designed for outdoor use inside a garden room. Mount infrared panels securely and out of reach, follow the manufacturer's clearance distances, and have a qualified electrician check the supply if you are adding more than a couple of kilowatts. A comfortable garden room is one you can relax in, and a few sensible precautions make that possible all year round.