A permanently installed split air conditioning system will usually cost less to run for the same level of cooling than a portable air conditioner because fixed systems are generally more energy efficient. Using the current Ofgem average electricity rate of 26.11 pence per kWh, a modern 2.5 kW fixed split system with a nominal electrical input of around 0.56 kW would cost roughly 15 pence per hour at that rated condition. Comparable portable units can draw around 0.8 kW to more than 1 kW, giving indicative costs of roughly 21 to 27 pence per hour. Actual running costs vary substantially because modern fixed systems reduce their power once the room reaches temperature.
At a Glance
If you are short on time, here is what you need to know.
Which generally costs less to run? A modern fixed split air conditioning system.
Why? Fixed systems are usually more energy efficient and do not rely on an exhaust hose through a window.
What does electricity currently cost? The Ofgem average electricity unit rate for a standard variable tariff paid by Direct Debit is 26.11 pence per kWh from July to September 2026.
How much might a fixed 2.5 kW system cost per hour? Using one current Daikin 2.5 kW system as an example, its nominal cooling input is 0.56 kW. At 26.11 pence per kWh that equates to approximately 15 pence per hour while operating at that nominal condition.
How much might a portable system cost? Current portable examples with similar nominal cooling capacities draw around 0.81 kW to 1.05 kW, equivalent to approximately 21 to 27 pence per hour at the same electricity price.
Are those guaranteed running costs? No. They are illustrations based on rated electrical input. Real consumption changes as the room temperature, weather and system output change.
Reading time: 11 to 13 minutes
Last reviewed: August 2026
Why Running Cost Matters More Than Purchase Price
When people first compare air conditioning, the obvious difference is installation cost.
A portable appliance can be bought and used immediately.
A permanent split system needs professional design and installation.
That makes the portable option look cheaper at first.
If the system is only going to be used for a few hours each year, that may be all that matters.
The calculation changes when cooling becomes something you rely on every summer.
A bedroom might be cooled for eight hours every night during a heatwave.
A home office could run throughout the working day.
An open plan living space might require cooling from afternoon until bedtime.
Over several summers, electricity consumption starts to matter much more.
What Is the Current UK Electricity Price?
Ofgem reviews its energy price cap every three months.
For the period from 1 July to 30 September 2026, the average electricity unit rate for households on a standard variable tariff paying by Direct Debit is 26.11 pence per kWh.
The actual rate you pay depends on your tariff, payment method and region. Fixed tariff customers may pay a different amount.
Ofgem has also confirmed an average electricity unit rate of 26.32 pence per kWh from October to December 2026.
For the examples in this article, we will use 26.11 pence per kWh because that is the applicable average rate at the time this guide was reviewed.
How Much Does a Fixed Air Conditioning System Cost to Run?
Let us use a real manufacturer specification rather than guessing.
Daikin publishes a nominal cooling capacity of 2.5 kW for its Perfera FTXM25R and RXM25R combination.
Its nominal electrical input during cooling is approximately 0.56 kW.
At an electricity price of 26.11 pence per kWh:
0.56 kW multiplied by 26.11 pence gives approximately:
14.6 pence per hour
For simplicity, around:
15 pence per hour
If it remained at that nominal electrical input for eight hours, the theoretical electricity cost would be approximately:
£1.17
Over thirty eight hour nights:
£35.09
That is not a prediction of what every customer will pay.
In reality, an inverter system normally changes its electrical consumption throughout the night.
Once the bedroom reaches the selected temperature, the system reduces its output and maintains comfort rather than continuing at the same nominal input constantly.
That means actual consumption can be lower than simply multiplying nominal input by the number of hours the system is switched on.
How Much Does a Portable Air Conditioner Cost to Run?
Again, manufacturer data gives us useful reference points.
A current DeLonghi Pinguino model provides approximately 2.5 kW of cooling with a published input power of 810 watts, or 0.81 kW.
At 26.11 pence per kWh, that represents approximately:
21 pence per hour
If it ran for eight hours at that input:
£1.69
Thirty eight hour nights would represent:
£50.76
Another 2.6 kW portable unit from ElectriQ lists a rated cooling input of 1.05 kW.
At the same electricity rate, that equates to approximately:
27 pence per hour
Eight hours would be around:
£2.19
Thirty eight hour nights would be around:
£65.80
Again, these are illustrative figures based on rated electrical input rather than a promise of actual household consumption.
What Do Independent Consumer Tests Say?
Which? tested portable air conditioners and reports that the average portable model in its testing costs around 22 pence per hour to run on its highest setting.
The models tested ranged from approximately 17 pence to 31 pence per hour based on an electricity unit rate of 26.11 pence per kWh.
Which? also states that split air conditioning systems tend to be more energy efficient than portable systems.
Energy Saving Trust provides a similar warning around portable running costs.
Its current guidance estimates typical portable air conditioning at around £4.84 to £6 for 24 hours of continuous operation in Great Britain.
The exact numbers will continue to change as electricity prices change, but the underlying efficiency difference remains important.
Why Is Fixed Air Conditioning More Efficient?
There is more going on than simply choosing a newer appliance.
The two systems operate differently.
The Compressor Is Outside
With a split system, the compressor and major heat rejection components sit outside the house.
The indoor unit is primarily responsible for moving conditioned air quietly around the room.
That separation makes the system better suited to permanent cooling.
There Is No Exhaust Hose Through the Window
A portable air conditioner needs to remove heat from the room.
Most achieve this using a flexible hose connected to a window.
Which? highlights one of the fundamental problems with this design.
If the hose passes through an open window without an effective seal, warm outdoor air can enter through the gap.
The appliance is therefore trying to cool the room while external heat is being allowed back inside.
A permanently installed split system does not require the bedroom window to remain open.
Fixed Systems Use Inverter Technology
Modern residential split systems vary their output.
When a bedroom is extremely warm, the system can work harder.
As the room approaches the chosen temperature, it reduces its output.
This is much more sophisticated than thinking of the system as simply being either fully on or completely off.
ClimateWorks Insight
One of the biggest mistakes when comparing running costs is looking only at the electrical rating printed on the product.
Comfort matters too.
If one system uses less electricity per hour but takes much longer to cool the room, the comparison becomes more complicated.
Equally, if one system reaches temperature quickly and then reduces its output, the amount of time it is switched on does not tell you how much electricity it actually consumes.
The meaningful comparison is:
How much energy does each solution require to keep the same room at the same comfortable temperature?
That is why seasonal efficiency and real room performance matter more than simply comparing wattage.
What Does SEER Mean?
When looking at permanent split air conditioning, you may see a figure called SEER.
SEER means Seasonal Energy Efficiency Ratio.
Rather than measuring the unit under only one operating condition, it provides an indication of cooling efficiency across a standardised cooling season.
For example, Daikin publishes a SEER of 8.65 for the 2.5 kW Perfera system referred to earlier, together with an A+++ cooling energy label.
Portable systems use different efficiency labelling and testing methods, so homeowners should be cautious about directly comparing a portable EER number with a split system SEER number.
They are not identical measurements.
The more useful point is that modern permanent split systems can achieve very high seasonal efficiency.
An Eight Hour Bedroom Example
Imagine two identical bedrooms.
Both need cooling during a prolonged spell of hot weather.
For a simple illustration, assume the equipment remained at its quoted input throughout the whole period.
A fixed 2.5 kW split system drawing 0.56 kW at nominal cooling would cost approximately:
£1.17 for eight hours
A portable system drawing 0.81 kW would cost approximately:
£1.69 for eight hours
A portable system drawing 1.05 kW would cost approximately:
£2.19 for eight hours
The difference for one night is not enormous.
Across thirty nights it becomes more noticeable.
Across several summers it grows further.
And these simple calculations do not capture the ability of an inverter split system to reduce its consumption after reaching the desired room temperature.
Real ClimateWorks Example in Hampshire
A typical Hampshire enquiry involves a master bedroom that becomes uncomfortable every summer.
The homeowner may have already tried temporary cooling and now wants something they can use every night without filling the room with equipment.
In this situation, running cost is only one part of the decision.
A permanent split system also allows:
- The window to remain closed
- Quieter indoor operation
- Accurate temperature control
- WiFi control on many models
- Heating during winter
The customer is therefore not simply replacing one cooling appliance with another.
They are changing the way the room is controlled throughout the year.
Real ClimateWorks Example in Surrey
Consider a home office used five days a week.
During a heatwave, cooling may be required from morning until late afternoon.
That amount of operating time makes efficiency more important than it would be in a guest room cooled three times each summer.
A permanent system can maintain the selected temperature throughout the working day.
When winter arrives, the same equipment can reverse its operation and provide heating.
For a room used throughout the year, looking only at the initial purchase cost gives an incomplete picture.
What About Noise?
Running cost is important, but bedrooms create another major difference.
The compressor of a fixed split system is outside the property.
Modern indoor units can consequently operate at very low sound levels.
Daikin lists sound pressure levels as low as 19 dBA for its Perfera wall mounted range.
Portable units contain the refrigeration system within the room.
Even good models therefore have more mechanical equipment operating beside you.
If the system will be used while sleeping or working, noise deserves to be considered alongside electricity consumption.
Can Solar Panels Reduce Air Conditioning Running Costs?
Potentially.
A permanent air conditioning system uses electricity.
If solar panels are generating while the system is cooling your home, some of that demand can potentially be supplied from your own generation.
This becomes particularly relevant for:
- Home offices occupied during the day
- South facing living rooms
- Garden rooms
- Households with battery storage
The exact saving depends on the solar system, battery, generation and electricity tariff.
It would therefore be misleading to describe air conditioning powered by solar as free.
But households with solar generation have an additional reason to think about when they use electrically powered cooling and heating.
Is Permanent Air Conditioning Always the Cheapest Choice?
No.
Running cost and total cost are not the same thing.
A permanent system has a higher initial investment.
If you require cooling for only a few hours every two years, the electricity savings alone are unlikely to recover that installation cost quickly.
The case becomes much stronger when:
- The same room overheats every summer
- Cooling is used regularly
- Quiet operation matters
- You want precise temperature control
- You intend to use the heating function during winter
- You expect to remain in the property for several years
This is why we prefer to understand how a homeowner actually uses the room before recommending equipment.
Common Mistakes When Comparing Running Costs
Comparing Cooling Capacity With Electricity Consumption
A 2.5 kW air conditioner does not necessarily consume 2.5 kW of electricity.
Cooling capacity and electrical input are different measurements.
Assuming the System Uses Full Power Whenever It Is Switched On
Modern inverter split systems change their electrical consumption as cooling demand changes.
Ignoring the Open Window
A portable exhaust hose arrangement can allow heat back into the room if the window is not properly sealed.
Ignoring Heating
A permanent reversible system also provides heating.
If you use it during winter, the investment should not be judged solely on summer cooling.
Using One Hourly Figure as a Guarantee
No responsible installer can tell every homeowner exactly what their air conditioning will cost per hour without knowing the equipment, room, conditions and electricity tariff.
Dr Julian Carter's Expert Commentary
“A homeowner should be cautious when somebody says an air conditioner costs exactly a certain amount per hour. Modern inverter systems constantly vary their output, so consumption changes throughout the day. The important point is that a properly designed fixed split system is generally a much more efficient way of providing regular cooling than a temporary appliance. The more frequently you use the room, the more relevant that efficiency becomes.”
Dr Julian Carter
Technical & Compliance Director
ClimateWorks
How the ClimateWorks Process Works
Step 1. Get Your Online Guide Price
Use the online quotation tool on the ClimateWorks website.
Answer a few questions about your property and the rooms you want to cool.
You will receive a guide price before deciding whether you want to take the enquiry further.
Step 2. Request a Site Survey
If the guide price fits your expectations, request a site survey.
We then confirm the system design, equipment size, indoor unit position, outdoor unit location, pipework, electrical requirements and how the room will be used.
Step 3. Receive Your Final Price
Following the survey, you receive a final quotation.
You can then accept or decline it.
The aim is to let homeowners understand the likely investment before committing to the next stage.
Frequently Asked Questions
How much does fixed air conditioning cost per hour to run?
It depends on the equipment and operating conditions. Using one 2.5 kW Daikin split system as an example, its nominal cooling input is 0.56 kW, equivalent to approximately 15 pence per hour at the current Ofgem average electricity rate of 26.11 pence per kWh. Actual consumption varies as an inverter system changes its output.
How much does a portable air conditioner cost per hour?
Which? reports an average of around 22 pence per hour on the highest setting among the portable systems it tested, with results ranging from approximately 17 pence to 31 pence per hour.
Does a 2.5 kW air conditioner use 2.5 kW of electricity?
No. The 2.5 kW figure normally refers to cooling capacity. The electrical power consumed can be much lower.
Is fixed air conditioning more efficient?
Generally, yes. Which? states that split systems tend to be more energy efficient than portable air conditioners.
Does fixed air conditioning use full power all night?
Not normally. Modern inverter systems reduce their output once the room approaches the selected temperature.
Can I use fixed air conditioning for heating too?
Yes. Modern residential split air conditioning systems normally operate as reversible air to air heat pumps and can provide heating during winter.
Do electricity prices change the calculation?
Yes. Every figure in this article changes if your electricity unit rate changes. Always use your own tariff when estimating costs.
Is running cost the only reason to choose permanent air conditioning?
No. Noise, temperature control, appearance, heating capability, long term use and convenience can be equally important.
References
Ofgem
The average electricity unit rate under the price cap for a standard variable tariff paid by Direct Debit from July to September 2026 is 26.11 pence per kWh.
Which?
Independent testing of portable air conditioners found average running costs around 22 pence per hour on maximum settings and notes that fixed split systems tend to be more energy efficient.
Energy Saving Trust
Energy Saving Trust estimates typical portable air conditioning running costs in Great Britain at approximately £4.84 to £6 for 24 hours of continuous use.
Daikin UK
Daikin publishes a nominal cooling input of 0.56 kW and seasonal cooling efficiency of SEER 8.65 for its 2.5 kW Perfera FTXM25R and RXM25R combination.
DeLonghi
Manufacturer specifications for the Pinguino PACEX93 Extreme list approximately 2.5 kW cooling capacity, 810 watts input power and an EER of 3.1.
Author Bio
Dr Julian Carter is Technical & Compliance Director at ClimateWorks and specialises in residential air conditioning, air to air heat pumps, system efficiency and indoor comfort. Drawing on practical experience from residential installations across Hampshire, Berkshire and Surrey, Dr Carter provides evidence based guidance to help homeowners understand the real costs and benefits of modern home heating and cooling systems.
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