How many kilowatts you need
As a rough guide, 2 to 3 kilowatts (kW) warms a room, a home office or a site cabin, 5 to 9 kW a garage or a small workshop, and 15 kW upwards a large workshop or a warehouse bay. A standard 13 amp socket tops out at about 3 kW, so most bigger models run on 3 phase power. An undersized heater runs constantly without reaching the temperature you set, so size for cold days, not mild ones.
Built for the home or the site
Domestic heaters with ceramic elements limit their own temperature and many cut out if knocked over, which suits a home or an office. Steel-bodied commercial and site heaters stand up to knocks and dust, and most have a thermostat that switches the heat off once the space is warm, plus a fan-only setting for summer. Larger site models can push warm air down a flexible duct into a room or tent they cannot stand in.
Sockets, transformers and running costs
On site, 110 volt models need a transformer big enough for their load, and 3 phase models need the matching 16, 32 or 63 amp socket, or a wired-in supply for the largest, fitted by a qualified electrician. Every kW uses one unit of electricity an hour on full heat, and a thermostat cuts that once the space is warm. Keep the air intake clear, vacuum dust from the grilles and never cover a running heater.