Air Con Running Cost Calculator (UK): Cost Per Hour Using Ofgem Price Cap Rates (2026)

This guide gives you a practical way to estimate what it costs to run air conditioning in the UK, down to a sensible “cost per hour” figure you can use for budgeting. It is built around the Ofgem energy price cap unit rates for 1 January to 31 March 2026, but the method works with any tariff, including fixed deals and business contracts.

You will learn how to:

• Find the electricity price (p/kWh) that matters for your estimate
• Identify the number on your air con spec sheet that represents electrical consumption (not cooling output)
• Convert “maximum power” into a realistic average using duty cycle and usage patterns
• build quick scenarios (per hour, per day, per month) and sanity-check them against your meter
• reduce running costs without compromising comfort, sleep, or indoor air quality

The quick formula (and the one mistake that ruins most estimates)

Cost per hour in one line

At its simplest, the running cost is:

Cost per hour (£) = electrical input (kW) × electricity unit rate (£/kWh)

If you keep everything in pence, it is:

Cost per hour (p) = electrical input (kW) × unit rate (p/kWh)

That is it. The hard part is choosing the right electrical input number and a realistic average for how your system actually runs.

kW output is not the same as kW input

Air conditioners are typically marketed by their cooling capacity, often expressed in kW (for example, “3.5 kW”). That figure is the amount of heat the system can remove from the room under test conditions. It is not the electricity it consumes.

For running costs, you need an electrical input power figure, usually shown as “power input”, “rated input”, or similar. On inverter systems, you may also see a range, such as “0.3–1.2 kW”. That range reflects modulation: the system draws less power when the room is close to the temperature and more when it is pulling hard.

If you only take one thing from this guide, take this: use the electrical input number, not the cooling capacity.

What this calculator can and cannot tell you

A calculator can give you a defensible estimate, but it cannot guess your building physics. Two identical units can cost very different amounts to run depending on: insulation levels, solar gain, air leakage, how often doors are opened, and how aggressively you set temperatures.

Use the calculator for budgeting, comparing scenarios, and spotting problems. If you want an engineering-level answer, measure consumption over a week (or use system monitoring, if available) and compare it to the estimate.

Benchmark tariff for early 2026: using the Ofgem price cap

The numbers we use (and why they change)

Ofgem publishes default tariff price cap rates every three months. For the cap period 1 January to 31 March 2026, the average electricity unit rate for a typical customer on a standard variable tariff paying by Direct Debit is 27.69p per kWh, with a daily electricity standing charge of 54.75p per day. These figures include VAT. You can see the published rates on the official Ofgem page: Changes to energy price cap between 1 January and 31 March 2026.

Unit rate vs standing charge: where the running cost fits

For air conditioning running cost estimates, the unit rate is the critical part because it scales with how long you run the system. The standing charge is a daily fixed cost you pay for being connected and billed, even if you use no energy that day. It matters for your total bill, but it does not change the “cost per hour” maths.

If you are modelling the difference between “air con on” and “air con off”, focus on the unit rate. If you are modelling your full electricity bill, add standing charges separately.

Use your own tariff if you have it.

The Ofgem price cap is a useful benchmark, but your actual unit rate can be higher or lower depending on region, payment method, meter type (including Economy 7), and whether you are on a fixed tariff. For the most accurate estimate, use the unit rate shown on your bill or in your supplier app. If you need to find the cap rates for your specific region and payment method, Ofgem provides a regional breakdown here: Get energy price cap standing charges and unit rates by region.

Step-by-step running cost calculator

Step 1: Get the right electricity unit rate (p/kWh)

Start with the number you are actually charged for electricity, in pence per kWh. If you are on a standard variable tariff and want a baseline, use 27.69p/kWh (Jan–Mar 2026 cap average). If you are on Economy 7 or another multi-rate tariff, use the relevant day and night unit rates and estimate how much of your air con use falls into each period.

Be careful with VAT and “all-in” pricing. Domestic bills usually show unit rates including VAT. Commercial contracts can vary, and some quotes separate VAT or other charges. Use the number you pay per kWh in practice.

Step 2: Find your unit’s electrical input (kW)

Next, find the electrical input power for your air conditioner. Depending on the system, you may find it in:

• the product datasheet or specification PDF (look for “power input” or “rated input”)
• the energy label or product page (sometimes shown as “input power”)
• the indoor or outdoor unit nameplate (often includes “input” or “max input”)
• installer commissioning documents (for fixed systems)

If you see a range, use it intelligently:

• The maximum input is useful for worst-case budgeting
• Minimum input is useful for steady-state, light-load running
• The average input is what you need for realistic monthly cost estimates

Step 3: Estimate how hard it runs (duty cycle)

Air conditioning does not usually pull maximum power continuously. Most modern systems are inverter-driven: once the room is close to temperature, the compressor slows down and power draw drops. The best way to reflect this is to use a duty cycle.

A simple duty-cycle approach is:

• Hot day, strong sun, doors opening: 70–100% of maximum input for long periods
• Typical summer day, steady occupancy: 40–70% of maximum input
• Night cooling in a well-insulated room: 20–50% of maximum input after the pull-down period

These are only planning ranges. Your real duty cycle depends on heat gains, insulation, set temperature, and how quickly you want comfort. If you can monitor power draw (smart meter, sub-meter, or built-in monitoring), replace guesses with measurements.

Step 4: Do the maths (per hour, per day, per month)

The most practical way to calculate is to pick a realistic average electrical input:

Average input (kW) = maximum input (kW) × duty cycle

Then calculate:

Cost per hour (p) = average input (kW) × unit rate (p/kWh)

Quick estimate table (Jan-Mar 2026 price cap electricity rate)

The table below uses an electricity unit rate of 27.69p/kWh as a benchmark. Replace the unit rate with your own tariff to personalise the numbers.

Use this table to sanity-check your calculations: if your unit’s average draw is around 1 kW and you cool for 8 hours a day, a monthly running cost in the region of £60-£70 at the cap rate is a reasonable order of magnitude. If your bill is dramatically higher, either your usage is higher, your tariff is higher, or your system is working harder than expected.

Worked example: turning a datasheet into a monthly cost

Imagine a wall-mounted unit with a maximum electrical input of 1.2 kW in cooling. You run it 6 hours per day through a warm month. The room is reasonably insulated, but it gets afternoon sun, so you assume an average duty cycle of 60%.

• Average input = 1.2 kW × 0.6 = 0.72 kW
• Cost per hour = 0.72 kW × 27.69 p/kWh = 19.94p (about £0.20)
• Monthly cost (30 days) = £0.20 × 6 hours × 30 = about £36

That is the sort of estimate you can make in a few minutes. If you then check your smart meter during a typical hour, you can refine your duty cycle up or down.

From nameplate numbers to real life: why air con often costs less than you fear

Inverter modulation changes the average dramatically

Inverter-driven systems are designed to avoid the harsh “on/off” cycling of older units. They ramp up to pull the room down quickly, then ramp down to maintain temperature. This matters because the average power draw over an evening is usually much lower than the maximum shown on the plate.

A useful way to think about it is to split usage into two phases:

1. Pull-down: the first 20-60 minutes, when the room is far from the target temperature and the power draw is higher.
2. Maintain: the remaining time, when the room is near target and power draw stabilises at a lower level.

If you only budget using the pull-down power level, your estimate will usually be too pessimistic. Duty cycle is the shortcut that brings your estimate back towards reality.

Set temperature is a running cost lever, not just a comfort choice

The bigger the gap between indoor and outdoor temperatures, the harder the system has to work. Small changes in the set temperature can reduce compressor effort without you feeling much difference.

Practical examples:

• If you set the bedroom to a very low temperature, the unit may run harder and longer, and then you may wake up cold and turn it off entirely.
• If you set a sensible target and use fan speed to manage how it feels, the compressor can stabilise at a lower load.

Your goal for running costs is a steady, moderate operation rather than an extreme pull-down.

Humidity can drive “hidden” energy use.

Air conditioning removes moisture as well as heat. On muggy days, some of the system’s work goes into dehumidification. That can increase the runtime compared to a dry day at the same temperature.

If your system has a “dry” or dehumidifying mode, it can be useful in shoulder seasons when the temperature is not extreme, but the humidity is uncomfortable. The exact energy impact varies by system and conditions, so treat it as a comfort tool rather than a guaranteed cost saver.

What drives running costs in UK homes

Solar gain and glazing

Sun through glass is often the biggest driver of summer overheating. South and west-facing windows, large roof lights, and unshaded patio doors can load the room with heat faster than you expect.

If your air con seems to run “non-stop” in the late afternoon, solar gain is often the reason. Cost control steps usually start with keeping heat out: blinds, reflective film where appropriate, external shading, and closing doors to isolate the zone you are cooling.

Top-floor rooms, loft conversions, and conservatories

UK housing stock often has rooms that behave like greenhouses. Loft conversions can overheat because they sit under the roof, and conservatories are designed to capture light, which also means capturing heat.

These spaces are exactly where “average duty cycle” assumptions can break. If you are cooling a loft conversion in a heatwave, plan for higher duty cycles and make sure the system is correctly sized for the room’s heat gains.

Ventilation behaviour and door discipline

There is a real difference between “cooling a room” and “cooling the outdoors”. If windows are open or doors are left ajar to a warm hallway, the system will keep paying that energy penalty.

A practical household routine is:

• Ventilate early morning or late evening when outdoor temperatures are lower
• Close windows and doors during peak heat if you are actively cooling
• Avoid frequent door opening to large warm spaces, if you can

This is less about being strict and more about being intentional. A few small changes can reduce runtime and cost without any equipment changes.

Running costs in offices and commercial spaces

Schedules and zones matter more than unit size

In commercial buildings, “wasted hours” are a common hidden cost. The system may be sized correctly, but it runs longer than needed because schedules are not aligned with occupancy.

If you are estimating running costs for an office, break the building into zones and ask:

• Which areas actually need cooling all day?
• Which rooms are used intermittently and could be on demand?
• Are meeting rooms being cooled at the same level as open-plan areas?

Zoning decisions affect both comfort and cost, and they can often be improved with controls rather than major hardware changes.

Door losses, high heat gains, and specialist rooms

Retail units, gyms, salons, and venues with doors opening frequently often see higher duty cycles because cool air escapes and warm, humid air enters. Similarly, rooms with a lot of equipment (comms rooms, production spaces, busy kitchens) can have large internal heat gains.

For cost estimates in these spaces, base your calculations on measured runtime or a conservative duty cycle, then adjust once you have even a week of data.

Maintenance is a running cost control measure.

When filters load up with dust, airflow drops. When coils are dirty, heat exchange becomes less efficient. Both can raise compressor effort and extend runtime.

If you want predictable running costs in a commercial setting, planned maintenance is usually cheaper than performance drift and reactive call-outs. Align checks with usage patterns, keep records of what was done, and treat airflow and cleanliness as efficiency controls rather than admin.

Cooling vs heating mode: how running costs change in winter

Many air conditioners are heat pumps

Most modern split systems can heat as well as cool, because they use heat pump technology. In heating mode, the system moves heat into the building rather than generating it directly. That can make heating cost-effective in mild weather, especially for small zones like home offices or bedrooms.

A simple way to estimate the heating cost per kWh of heat

If you know (or assume) the system’s coefficient of performance (COP) at the conditions you care about, you can estimate the effective cost of delivered heat. The simplified relationship is:

Cost per kWh of heat (p) ≈ , electricity unit rate (p/kWh) ÷ COP

For example, if your electricity unit rate is 27.69p/kWh and the system averages a COP of 3 under typical conditions, the effective heat cost would be about 9.23p per kWh of heat. This is a planning estimate only, but it helps you compare like with like.

Cold snaps, defrost cycles, and realistic expectations

In colder weather, the outdoor unit has less heat available and may need to defrost periodically. That can reduce seasonal efficiency and increase runtime. If you are using air-to-air heating as a primary heat source, treat it as a system design question rather than an “appliance” decision.

A professional survey can clarify whether the proposed system will meet your comfort needs efficiently throughout the year.

How to cut running costs without sacrificing comfort

Set sensible targets and use the fan strategically

Extreme set temperatures typically cost more and can feel worse. A better approach is to aim for steady comfort and use fan speed to control how it feels in the room. For sleep, many systems have a quiet or night mode that prioritises lower fan noise and steadier operation.

Keep heat out before you pay to remove it

Heat management steps that often outperform gadgetry:

• block direct afternoon sun on south and west-facing glazing
• reduce internal heat gains (turn off unused equipment, use efficient lighting)
• Close doors to isolate the room you are conditioning
• Pre-cool earlier in the day if your home holds heat into the evening

These steps reduce the load on the compressor, which is where most energy is used.

Keep the system clean and breathing

The lowest-cost maintenance is usually the simplest:

• clean or replace filters as recommended by the manufacturer
• keep supply and return paths unobstructed (do not block indoor unit airflow with furniture)
• Watch for early signs of problems like icing, unusual noise, or persistent water leaks.

If you want performance to stay consistent year after year, schedule servicing. This is especially important in commercial environments where the system runs for longer hours. Controlled Climate offers planned servicing and maintenance options here: air conditioning service and maintenance.

When high running costs point to a system problem (or a design issue)

Signs your system is working harder than it should

If your estimate suggests a certain running cost but your bill is far higher, look for these common drivers:

• dirty filters or coils: reduced airflow, longer runtime
• Incorrect settings: very low setpoint, high fan, constant operation when the space is unoccupied
• air leakage and heat gain: open windows, poorly shaded glazing, doors open to warm areas
• undersizing: the unit cannot reach the temperature, so it runs flat-out
• oversizing with poor control: short cycling (more common with older non-inverter systems)

When to stop DIY and call an engineer

Some issues should not be treated as “a quick tweak”. If you see repeated icing, the unit frequently trips, airflow is unusually weak, or the system is leaking persistently, you need a professional assessment. These symptoms can indicate refrigerant issues or drainage faults, and continuing to run the system can make the problem worse.

If you are local to Bristol and want a professional view, use the contact page to describe the symptoms and your system type.

When the right answer is a survey and a better design

Running costs are often decided at the design stage. Correct sizing, sensible unit placement, and good control strategy typically matter more than chasing a slightly higher efficiency label.

If you are planning a new install or you suspect your current system is poorly matched to the space, a site survey is the sensible next step. Controlled Climate offers a free air conditioning survey request form here: Free Air Conditioning Survey.

If you want to explore residential options first, see the home installation overview: Home Air Conditioning Installation.

Summary

Running cost estimates do not need to be guesswork. Start with your electricity unit rate (use the Ofgem cap as a benchmark if you need to), then multiply it by your air con’s electrical input, not its cooling capacity. Add realism using duty cycle, because inverter systems rarely run at maximum power for long periods.

If your numbers look high, reduce the cooling load first: shade glazing, close doors, and avoid extreme set temperatures. Keep filters clean and service the system so it can move air and exchange heat efficiently. Where costs still do not make sense, treat it as a design or maintenance problem rather than a “normal” cost of comfort.

Frequently Asked Questions

How much does it cost to run air conditioning per hour in the UK?

It depends on your electricity unit rate and your unit’s average electrical input. Using the Jan–Mar 2026 Ofgem cap average of 27.69p/kWh, a system averaging 1.0 kW costs about 28p per hour. Double the input, and you roughly double the cost.

Why does my air con say “3.5 kW” if it does not use 3.5 kW of electricity?

The 3.5 kW figure usually describes cooling output (capacity), not electricity use. For running costs, you need the electrical input, often shown separately as rated or maximum input power.

Is the Ofgem price cap a cap on my total bill?

No. The cap limits what suppliers can charge per unit of energy and for the standing charge on default tariffs. Your total bill still depends on how much energy you use.

Does the price cap apply if I am on a fixed tariff?

Fixed tariffs have their own unit rates and standing charges, which can be above or below the cap. For your calculator, use the rates you actually pay on your tariff.

Should I leave the air con on all day to save money?

Not automatically. Inverter systems can maintain temperature efficiently, but running all day only makes sense if your home holds heat and you would otherwise do repeated pull-downs. Compare scenarios using the calculator and your actual lifestyle.

Is “dry mode” cheaper than cooling?

Dry mode focuses on reducing humidity, which can improve comfort at higher temperatures. Energy use varies by system and conditions. Use it when humidity is the problem, and verify by checking your meter over a few hours.

Why do my running costs spike during heatwaves?

Heatwaves increase outdoor temperatures, solar gain through windows, and indoor heat gains, so the unit runs harder and for longer. Use shading, close doors, and consider pre-cooling earlier to reduce peak load.

When should I service my air conditioning to keep it efficient?

If you rely on the system regularly, annual servicing is a common baseline, with more frequent checks for heavy commercial use. Clean filters more often, as restricted airflow can increase runtime and cost.