Annexe Knowledgebase

How best to heat a garden annexe will depend on a number of factors, size of annexe, the amount of glass and i’s thermal properties, the aesthetics, and the cost. Here we offer ten options that are available.

1. Electric convection heaters are the probably the most widely-used option. They are excellent for garden annexes, as they heat the air quickly and can be free standing or wall mounted. Most are available with 24-hour timers and are thermostatically controlled, which is ideal to pre-warm an annexe before your day begins, to switch themselves off if you get some nice sunshine, and to prevent annexes becoming too cold overnight. They are relatively cheap to buy and install, not requiring a separate energy source if you have electricity supply already.

2. Electric radiators are available in both traditional and modern styles. Like central heating radiators in the home, they are wall mounted but have an electric element instead. They are slower to heat up than convection heaters and offer slightly less temperature control, although they too can be linked to thermostats and timers to pre-warm your garden annexe.

3. Electric oil filled radiators tend to be free standing, which offers usage flexibility but at the price of taking up floor space. The oil retains heat, maintaining warmth for longer after they are switched off, which again can be via a thermostat or timer. Breadth of choice and styling tends to be more limited than wall-mounted heaters as above, but they are low in cost and widely available with no installation required.

4. Wood burners look fantastic in a timber annexe, whether traditional or contemporary, and they perform well too. They warm quickly, retain heat and are carbon-neutral if you can use a sustainable local fuel source. Do please remember they must be professionally installed by a HETAS engineer to ensure your safety. The cost of a stove unit itself may appear attractive, but do the math including the flue and installation which can add up to a larger sum.

5. Underfloor heating can be effective as a secondary heat source. It frees up wall space and feels lovely underfoot, but may not be effective or economical as the main heat source. For most garden annexe, electric underfloor heating runs on a mesh element which is cut to size and fitted below the floor. The draw backs are that it is more expensive to install than electric heaters, it limits the choice of floor coverings and any maintenance problems will require the floor being lifted.

6. Air conditioning can both heat and cool the air and help maintain a constant temperature and humidity level. It can be a good choice in garden annexes where the building is in full sunlight all day. The new generation of air conditioners do not require external or unsightly refrigeration units which can create a noise disturbance for you and your neighbours, they are low noise, slimline, internally mounted units and are relatively cheap to run.

7. Bottled gas run on propane and are a good idea for annexe that have limited mains electricity. They are a practical choice if you use bottled gas in your home and you can add an extra one or two to a delivery, otherwise the time and cost of obtaining gas bottles needs to be factored in. Gas bottles can be installed outside the annexe to feed a fixed gas heater, or there are freestanding heaters which enclose a small gas bottle. These tend to be bulky and short on aesthetic appeal. More importantly, they need adequate ventilation to prevent the build up of water vapour or any risk of toxic fumes.

8. Infrared heat the person, not the air around them. They are economical to use, and effective provided that you can design your space so that you are in line with the heater.

9. Solar heat warms water that is passed through a series of tubes mounted on the roof. In the home these systems are used to pre-warm water feeding into a conventional heating boiler. In garden annexes, a collector tends to feed a single radiator with warmed water.

10. Design your annexe to limit the heating and cooling you need. South facing windows and heat-retaining dark floor tiles will collect passive solar heat, while overhanging eaves will allow your garden room to collect low sun in winter but shade it from high sun in summer. In a quality garden annexe, good floor and roof insulation is a must, as is high quality double glazing and draught proofing for doors and windows.