Heating a Garden Room in Winter

Insulation Comes Before Any Heater

Before you spend a penny on a heater, spend it on the shell of the building. A garden room that loses heat through single-glazed windows, an uninsulated floor and draughty door frames will defeat even a 3kW heater, and you will pay for that defeat every evening from November to March.

Start with the roof, because heat rises and escapes. Then work down: walls, floor, then doors and windows. In a timber-framed garden room, 50mm of rigid PIR board between the studs gives you a U-value of roughly 0.44, which is adequate. Push that to 100mm and you get closer to 0.22, which is a genuine difference you can feel at ankle level. Line the inside face with foil-backed board and tape the joints; gaps at the edges undo most of the good work.

Then tackle air movement. A brush or rubber seal on the door, a threshold strip, and a decent multi-point lock with compression gaskets will cut draughts dramatically. If your garden room is a converted shed with a felt roof and no floor insulation, a thick rug and a layer of 25mm foil-faced insulation underfloor boards is money well spent.

Electric Panel Heaters

Panel heaters are the simplest option and the one most garden room owners start with. They are cheap to buy, silent, and easy to mount on a wall clear of furniture. A 1.5kW to 2kW convector panel will bring a well-insulated 10 to 12 square metre room up to temperature in twenty minutes or so.

Their weakness is that they heat the air rather than the objects in the room, so the warmth disappears quickly once switched off, and they are unforgiving of poor insulation. Run a 2kW panel for six hours at full draw and you are using 12kWh, which at around 25p per unit is roughly £3. In practice a thermostat will cycle it, so you might use half that — but it is still the most expensive way to heat the space.

Choose one with a digital thermostat and a seven-day timer rather than a basic dial. A wall-mounted panel with a built-in thermostat sitting in a cold corner will overrun constantly.

Infrared Heaters

Infrared panels work differently. Instead of warming air, they emit radiant heat that warms people, floors and furniture directly. That makes them feel almost instant, and it suits a garden bar or a den where you flit in and out rather than sitting for hours.

A 350W to 700W infrared panel can make a small seating area comfortable, and because you feel the benefit within seconds, you tend to run it for shorter bursts. That is where the savings come from — not from the technology being magically cheaper per unit.

• Best for: occasional use, small rooms, above a desk or seating position.
• Less good for: heating a whole room evenly, or warming a space you leave running all day.
• Watch out for: mounting height and angle. Ceiling-mounted panels need to point down at where people actually sit.

Wood Burners

Nothing beats a small wood burner for atmosphere, and if you have a ready supply of seasoned hardwood it can be the cheapest heat per hour by a wide margin. A 4kW to 5kW stove is plenty for a garden room of up to 15 square metres, assuming the insulation is decent.

The practicalities matter more than the romance. You need a proper flue, a hearth, clearance from combustible materials, and in most cases a building regulations check — a garden room is not exempt just because it is at the end of the lawn. Smoke control areas cover many UK towns, so check whether you need a DEFRA-exempt appliance.

Logs must be seasoned to below 20 per cent moisture. Wet wood gives you a smouldering fire, blackens the glass and sends most of its energy up the chimney as tar and steam. Buy kiln-dried, or season your own for a full year under cover.

Thermostats, Timers and Running Costs

Whatever you install, control is what keeps the bill sane. A programmable thermostat set to 18°C rather than 22°C can cut your heating energy by a third. Set a background temperature of 12°C to 14°C when the room is empty to keep damp at bay, and bring it up half an hour before you use it with a timer or a smart plug.

Zone your thinking too. Heating a garden office for a working day is a different job from heating a bar for a Saturday evening. If you use the room for both, an infrared panel over the desk plus a low-background panel heater may beat one big unit running flat out.

Putting Together a Sensible Setup

A workable combination for most UK garden rooms looks like this:

• Insulate the roof, walls and floor properly, and seal the door.
• Fit a thermostatic panel heater on a timer for consistent background warmth.
• Add a small infrared panel above the spot where you actually sit.
• Choose a wood burner instead if you want the fire, the space and the fuel supply to justify it.
• Keep a dehumidifier or a vent open in shoulder seasons to control condensation.

Get the shell right, keep the temperature moderate, and a garden room stays usable right through the coldest weeks without a frightening meter reading.