Key checks
When to call an engineer
If the problem involves fixed wiring, high-current heating equipment, repeated tripping, unvented hot water or uncertainty about the supply arrangement, testing is safer and usually faster than swapping parts.
Related specialist pages
Start with insulation and intended use
A garden office used eight hours a day needs a different heating strategy from an occasional gym or hobby room. Floor, roof and wall insulation, glazing and air leakage can dominate the heat demand.
Direct electric versus wet electric heating
For a single small outbuilding, a direct electric panel or underfloor system is often simpler than installing a wet system and electric boiler. Larger annexes with several rooms and hot-water demand may justify a wet system, but only after the electrical supply and cable route are assessed.
Submain capacity matters
The outbuilding supply must accommodate heating alongside sockets, lighting and any other equipment. The existing protective device and cable cannot be assumed suitable simply because spare ways exist in a consumer unit.
Reviewed 9 September 2026 · NICEIC-registered electrical work · G3 unvented hot-water qualified · Dimplex Pro / Quantum installer training.