How Much Electric Does a Heater Use

Electric heaters are a convenient way to add quick warmth to a room, top up heat in cold spots, or keep a home office comfortable without running whole-house heating. With energy budgeting high on the agenda, a common question is how much electricity a heater actually uses. The answer depends on the heater’s wattage, how long it runs, the building’s insulation, and how the controls are set. This article explains the figures in simple terms, shows you how to estimate real running costs, and sets out the safety and compliance points that apply in UK homes and rented properties.

Watts, kilowatt-hours, and what they mean for your bill

Every electric heater has a power rating in watts. A 2,000 watt appliance is the same as 2 kilowatts. Energy suppliers bill in kilowatt-hours, which is the power multiplied by time. If a 2 kW heater runs for three hours, it uses 6 kWh. To estimate cost, multiply the kWh by your unit rate. With a typical example rate of 30 pence per kWh, that three-hour session costs £1.80. The method is the same for any heater and any tariff. Power in kW times hours equals kWh, and kWh times your price per kWh equals cost.

It is important to remember that many heaters do not draw full power continuously when a thermostat is controlling the room temperature. Once the set point is reached the element cycles on and off. This duty cycle means the average consumption over an hour can be lower than the nameplate wattage suggests, especially in a smaller or better-insulated room.

Types of electric heater and typical usage

Portable fan heaters and convector heaters often sit between 1.5 and 2 kW. They warm air quickly and are useful for short bursts of heat. Oil-filled radiators commonly range from 1 to 2.5 kW. They are slower to heat up but their thermal mass helps smooth out cycling, which can feel more comfortable for longer sessions. Panel heaters and wall-mounted convectors are usually 0.5 to 2 kW, sized to the room. Infrared panel heaters tend to have lower wattages for targeted comfort because they warm people and surfaces directly rather than heating a large volume of air.

All resistive electric heaters convert almost all the electricity they draw into heat in the room. That makes them simple to understand but it also means a kilowatt of electricity delivers a kilowatt of heat. Devices that move heat rather than create it, such as air-to-air heat pumps, can deliver several kilowatts of heat per kilowatt of electricity. That is why a heat pump is more economical for whole-home heating, while plug-in heaters are best for spot heating and short, focused use.

Real-world cost examples you can adapt

A 2 kW fan heater running for two hours uses 4 kWh. At 30 pence per kWh that is £1.20 for the session.
A 1.5 kW oil-filled radiator running for five hours uses 7.5 kWh. At the same rate the cost is £2.25.
A 750 watt panel heater running for four hours uses 3 kWh. At the same rate the cost is 90 pence.
A 500 watt frost-protection heater left on all day uses 12 kWh. At the same rate that is £3.60 for the day.

It helps to scale these figures to monthly use. A 2 kW portable heater used for four hours a day across a 30-day month totals 240 kWh. At 30 pence per kWh that adds roughly £72 to the bill. If the thermostat is satisfied for a portion of that time the true figure will be lower. If the room is large or poorly insulated the heater will cycle for longer and the figure will be higher.

Why the same heater costs different amounts in different rooms

Two rooms can behave very differently with the same heater. Heat loss depends on room size, outside temperature, insulation quality, window area, and air leakage. A small, well-insulated bedroom with modern double glazing and draught-proofing will hold heat well, so a thermostat has time to switch the element off. A larger lounge with single glazing, gaps around the door, and a cold external wall will lose heat faster and keep the element energised for more of the hour.

Simple building fabric improvements reduce running costs. Closing curtains at dusk, fitting thermal blinds, using draught excluders, and ensuring trickle vents and extract fans are used correctly so that moisture is controlled without excessive ventilation loss will all help. If you own the property, upgrading loft insulation and considering secondary glazing for leaky windows make a noticeable difference to how long a heater needs to run.

Controls that make a measurable difference

A heater with a good quality thermostat avoids overshooting the set point. An electronic thermostat measures more precisely than a basic mechanical one, which can reduce unnecessary cycling. A programmable timer allows pre-heating before occupancy and shut-off after bedtime, so the appliance only runs when heat is useful. Many modern panel heaters and some oil-filled radiators include an eco mode that reduces the set point slightly once the room is warm. Dropping the set temperature by a degree or two often saves a meaningful amount over a month while remaining comfortable.

Avoid using high heat settings with a window open. Warm air lost through the opening forces continuous heating and quickly inflates consumption. If fresh air is needed, ventilate briefly and fully, then close the window so the thermostat can regain control. In bedrooms, pre-heating for a short period before sleep and then relying on bedding for warmth is often more economical than running a heater all night.

Portable heaters versus fixed electric heating

Portable heaters plug into a socket on an existing circuit. They are flexible and require no installation work, which is useful in a home office or when heating a single room for a short period. For regular daily use, a fixed electric heater on its own circuit with an integral thermostat can be safer and more efficient. Fixed appliances should be installed in line with the Wiring Regulations. Cable sizing, protective devices, and the means of isolation must suit the load and location, and bathroom zones require special consideration for IP ratings and RCD protection.

Under Part P of the Building Regulations, most fixed wiring work in dwellings must be designed and installed by a competent person and, where it is notifiable, certified to Building Control. Using a contractor registered with a competent person scheme means design, installation, testing, and certification are handled correctly. For simple additions like a single fused connection unit supplying a fixed panel heater outside a bathroom, the work may be non-notifiable, but it still must comply with BS 7671 and be tested with an appropriate certificate issued.

Plug-in safety, loading, and the consumer unit

Portable heaters draw a significant current. A 2 kW unit at 230 V draws around 8.7 A. Running two such heaters on the same ring final circuit alongside a kettle or tumble dryer can take the circuit close to its design limits. Heaters should be plugged directly into a wall socket rather than a multi-way adaptor. Extension reels left coiled can overheat under sustained loads. In older properties with ageing accessories or marginal connections, high continuous currents expose weaknesses. Signs such as warm plugs, discoloured sockets, or nuisance tripping should be investigated by an electrician.

Modern consumer units with residual current device protection improve safety for portable appliances, especially in rooms where trailing leads can be damaged. If your home still relies on old rewireable fuses or lacks RCD protection, a consumer unit upgrade is well worth discussing with a qualified electrician, both for safety and for compliance with current standards.

Rented homes, HMOs, and landlord obligations

Private rented homes in England must have an Electrical Installation Condition Report at least every five years, with remedial work completed where defects are found. This inspection checks that circuits, protective devices, and accessories are suitable and safe for expected loads. In houses in multiple occupation, portable heaters should be risk assessed, kept clear of combustibles, and ideally limited to devices with tip-over protection and thermostats. Providing adequate fixed heating reduces reliance on portable appliances that tenants may operate unsafely.

Where panel heaters are provided as part of the heating system, the supply must be designed for simultaneous loads. Diversity may be applied in design for fixed heating circuits, but socket circuits should not be relied upon to carry whole-home heating for extended periods. Clear user instructions about safe operation, ventilation, and keeping heaters unobstructed help reduce hazards.

When a heater seems to use more than expected

If a heater is running for far longer than you expect, there are usually straightforward causes. The thermostat may be set high so it never quite satisfies. The room may be losing heat through gaps around windows and doors. The heater may be undersized for the space, forcing long run times for little temperature rise. Sometimes the true culprit is lifestyle. A door opened frequently to an unheated hallway or conservatory will drain heat as quickly as the heater supplies it. Working through these points often reduces consumption without sacrificing comfort.

A plug-in energy monitor can help quantify usage. These devices show real-time watts and cumulative kWh. By comparing figures at different thermostat settings and with simple draught-proofing in place, you can see which changes save the most.

Smart tariffs, timers, and practical budgeting

If your supplier offers a time-of-use tariff, running panel heaters or oil-filled radiators during cheaper periods can reduce cost, though you still use the same kWh. Pre-heating a room before a cheap window ends, combined with good insulation and closed doors, can carry comfort further into the peak period. Timers ensure the appliance turns off as soon as heat is no longer required. In a home office, aim to arrive to a pre-warmed space rather than running the heater all day.

Budgeting is easier when you translate heater time into weekly kWh. For example, a 1.5 kW radiator used three hours a day across five working days totals 22.5 kWh per week. At 30 pence per kWh that is £6.75. If you reduce the set point and shave the duty cycle so the average draw over the three hours is closer to 1.1 kW, weekly use drops to about 16.5 kWh, or £4.95, with little change in comfort.

Bathrooms, plug-in heaters, and special locations

Bathrooms require extra care. Portable heaters should not be used in zones where they can be splashed, and trailing flexes present significant risks. Fixed electric heating in bathrooms must be correctly IP rated and protected by a 30 mA RCD. For towel warmers and panel heaters, a permanent connection through a suitably rated isolator or fused spur is normally required. Heating controls should be positioned outside zones unless built into a suitably rated unit. If in doubt, seek advice from a registered electrician before adding any electrical heating in a bathroom or shower room.

Bringing it all together

The running cost of an electric heater is predictable once you know the power in kilowatts, the hours of use, and your tariff. Resistive heaters convert electricity to heat with near total efficiency, so a kilowatt in is a kilowatt out. That makes controls, insulation, and sensible operation the real levers for saving money. Use thermostats wisely, warm only the rooms that are occupied, reduce draughts, and prefer fixed, well-controlled heating for regular use. For landlords and those managing shared accommodation, ensure the electrical installation is up to standard, that fixed heating is adequate, and that portable appliances are used safely. When you need quick, targeted warmth, a portable heater is a practical tool. For whole-home heating or long daily schedules, consider more efficient systems and ensure any new fixed wiring complies with the Building Regulations and the current edition of BS 7671.

With a clear understanding of the numbers and a few practical measures, you can keep rooms comfortable and avoid unpleasant surprises on your electricity bill.