TL;DR
- Sustained heat increases electricity use through fans, refrigeration and air conditioning units where present.
- The current Ofgem price cap electricity unit rate is 24.50p per kWh.
- A 50W fan running 24 hours costs around 29 pence at current rates.
- A portable air conditioning unit running 8 hours per day costs around 3 pounds per day.
- Passive cooling measures can reduce indoor temperatures by several degrees at no cost.
How Does a Heatwave Affect Your Energy Bill?
Unlike cold snaps, which drive significant increases in gas consumption for heating, UK heatwaves have a more modest effect on most household energy bills. The majority of UK homes do not have air conditioning, so the primary impact is on electricity rather than gas.
The main drivers of increased electricity use during a heatwave are electric fans running for extended periods, refrigerators and freezers working harder to maintain temperature when ambient room temperature is high, increased fridge and freezer door opening, and where present, portable or fixed air conditioning units. For households with solar panels, prolonged sunshine also increases generation, which can partially offset higher consumption costs for those with export or self-consumption arrangements.
Running Costs at the Current Price Cap
The Ofgem price cap for April to June 2026 sets the electricity unit rate at 24.50p per kWh for default tariff customers, with a standing charge of 61p per day. Gas rates are set at 6.24p per kWh with a standing charge of 31p per day. These rates apply to the majority of UK households on standard variable tariffs.
A typical electric fan uses between 30 and 70 watts. Running a 50W fan continuously for 24 hours at 24.50p per kWh costs approximately 29 pence. Running two fans for eight hours per day over a week of hot weather adds roughly two pounds to the electricity bill, which is noticeable but not significant for most households.
A portable air conditioning unit suitable for a standard UK living room typically uses between 1,000 and 2,500 watts. Running a 1,500W unit for eight hours per day at 24.50p per kWh costs approximately 2.94 pounds per day, or around 20 pounds for a week. For households already under financial pressure, this is a meaningful additional cost and the decision to run air conditioning warrants careful consideration against the free alternatives available.
A fridge-freezer in a kitchen that reaches 30 degrees indoors works harder to maintain its set temperature. Studies by appliance manufacturers suggest energy consumption for refrigeration can increase by 15 to 25 percent when ambient kitchen temperature rises significantly above normal. For an average fridge-freezer consuming around 150 kWh annually, this represents an additional cost of a few pounds over a sustained hot period rather than a dramatic increase in bills.
Free and Low-Cost Cooling Measures
Keep windows on the shaded side of the property open overnight to allow cool air to circulate, and close windows and blinds or curtains on the sunny side during the day before the outside temperature rises. This passive cooling approach can reduce indoor temperatures by several degrees compared to leaving windows open throughout the day and is recommended by both the NHS and the UK Health Security Agency as the primary response to hot weather in UK homes.
Hang damp sheets or towels near open windows or in front of fans. Evaporative cooling is less effective in humid conditions but can provide meaningful relief in dry heat. A spray bottle of cold water used periodically provides a similar direct effect.
Avoid heat-generating appliances during the hottest part of the day. Ovens, tumble dryers and dishwashers all generate significant heat as a byproduct of their operation. Shifting these to early morning or evening reduces indoor heat build-up during peak temperature hours and may also reduce electricity costs for households on time-of-use tariffs such as Octopus Agile or Economy 7, where overnight rates are substantially lower.
Keep the loft hatch closed during the day. Loft spaces in direct sun can reach very high temperatures and an open hatch allows hot air to circulate down into the living space. This is a commonly overlooked source of indoor heat gain in UK homes during summer.
Heat Health Alerts and Vulnerable Households
The UK Health Security Agency issues Heat Health Alerts when temperatures are forecast to reach levels that pose a risk to health. The alerts run from Level 1 (summer preparedness, year-round) to Level 4 (national emergency). A Level 3 alert is issued when temperatures are forecast to reach 30 to 32 degrees Celsius during the day and 15 to 17 degrees at night for at least two consecutive days, depending on the region of England concerned.
Older people, young children and those with pre-existing health conditions including cardiovascular disease, respiratory conditions and diabetes are most at risk during sustained hot periods. NHS guidance recommends keeping rooms used for sleeping below 24 degrees where possible, staying hydrated throughout the day, and checking on vulnerable neighbours and relatives during prolonged hot spells.
Local councils and NHS services may activate additional support during Level 3 and Level 4 alerts, including opening cool spaces in libraries, leisure centres and community buildings for those without adequate cooling at home. Details of local cool spaces are typically published on council websites during alert periods.
Energy Debt and Prepayment Meters
For households already carrying energy debt or on prepayment meters, a period of hot weather that increases electricity use can place additional pressure on finances. Ofgem rules require energy suppliers to take reasonable steps to support customers in debt, including offering repayment plans that reflect ability to pay. Customers struggling with energy debt should contact their supplier directly. Citizens Advice operates a free energy advice service and can assist with negotiations with suppliers and applications for energy grants and emergency support funds.
Smart Meter Users
Households with a smart meter and in-home display can monitor the real-time cost of running cooling appliances during a heatwave. This can help identify which appliances are driving consumption and inform decisions about when and how long to run them. Smart meter data also allows comparison of daily consumption during hot weather against a baseline, which can be a useful tool for understanding the actual cost of the hot period on the bill.
Frequently Asked Questions
How much does it cost to run a fan during a UK heatwave?
A typical 50W fan running continuously for 24 hours costs approximately 29 pence at the current Ofgem cap rate of 24.50p per kWh. Running it for eight hours per day over a week costs around 70 pence.
What is the current electricity unit rate in the UK?
The Ofgem price cap for April to June 2026 sets the electricity unit rate at 24.50p per kWh for default tariff customers. Rates vary for customers on fixed tariffs.
Does a heatwave increase gas bills?
Not significantly for most households. Hot weather reduces demand for space heating, which is the main driver of gas consumption. Gas use for cooking and hot water continues as normal. The net effect on gas bills during a summer heatwave is generally small.
What should I do if I cannot afford to cool my home?
Contact your energy supplier about hardship support. Citizens Advice provides free energy advice and can help with applications for emergency grants. Local councils may open cool spaces in public buildings during high-level heat alerts.
At what temperature does a Heat Health Alert get issued?
A Level 3 Heat Health Alert is issued when temperatures are forecast to reach 30 to 32 degrees Celsius during the day and 15 to 17 degrees at night for at least two consecutive days, depending on the region of England concerned.
Sources: Ofgem price cap | UKHSA heat guidance | NHS heatwave advice
