How hot is the UK actually getting?
The short answer: measurably, consistently hotter – and the extremes are pulling away fastest.
According to the Met Office's State of the UK Climate 2024 report, the UK has warmed at roughly 0.25°C per decade since the 1980s, leaving the most recent decade (2015–2024) about 1.24°C warmer than the 1961–1990 baseline. The headline figures that matter for building owners are about frequency, not just averages:
- The number of days reaching 5°C above the 1961–1990 average has doubled; days 8°C above have trebled; and days 10°C above have quadrupled, comparing 2015–2024 with 1961–1990
- 2025 was provisionally the UK's warmest year on record, joining 2022 and 2023 in the top three warmest years since 1884 (Met Office, 2026)
- In July 2022 the UK exceeded 40°C for the first time on record (40.3°C at Coningsby, Lincolnshire). The Met Office now estimates a 50:50 chance of another 40°C day within roughly 12 years – a risk over 20 times higher than in the 1960s
The practical takeaway for facilities and estates teams: a building specified for the climate of even 20 years ago is increasingly being asked to perform in a different one. This is why "how to keep an office cool in a heatwave" has moved from a reactive search to a strategic procurement question.
What does heat do to people at work?
Heat doesn't just make a room uncomfortable – it measurably degrades how people think, feel and perform. And the impact lands differently depending on the working environment.
The most robust evidence comes from indoor-environment research collated by the Lawrence Berkeley National Laboratory, which found that office work performance peaks at around 21–22°C and declines as temperatures rise beyond roughly 23–24°C. A 2024 meta-analysis of 30 studies confirmed that moderately raised temperatures significantly increase response times and reduce accuracy, with the effect becoming pronounced after just one hour of exposure – and worse for cognitively demanding tasks.
At the higher temperatures now being recorded in UK summers, the losses are stark. Research led by Professor George Havenith at Loughborough University's Environmental Ergonomics Research Centre found productivity dropped by 35% once temperatures exceeded 35°C at 50% relative humidity, and by as much as 76% at 40°C and 70% humidity.
Offices and contact centres
Concentration, decision-making and patience all decline. Error rates climb in the afternoon as heat accumulates. For knowledge work and customer-facing teams, the cost is invisible on a thermostat but very visible in output and service quality.
Schools and education
Excessive classroom heat reduces learning outcomes and disproportionately affects disadvantaged pupils. The scale isn't hypothetical: 104 schools closed during the July 2022 heatwave. For school estates teams, reliable cooling is increasingly a safeguarding and attainment issue, not a luxury.
Retail, hospitality and public buildings
Overheated shops, libraries, banks and reception areas drive customers away and place staff under genuine physical strain – dehydration, fatigue, fainting and heat exhaustion all become real risks during sustained hot spells.
Healthcare and care settings
Vulnerable occupants – the elderly, the unwell, the very young – are least able to regulate their own temperature, making consistent, controllable indoor climate a duty-of-care priority.
Is there a legal maximum workplace temperature in the UK?
No – there is currently no legal maximum workplace temperature in the UK. But that does not mean employers are off the hook, and the regulatory direction of travel is clear.
Under the Workplace (Health, Safety and Welfare) Regulations 1992, employers must maintain a "reasonable" indoor temperature. The Health and Safety Executive (HSE) sets a recommended minimum of 16°C (13°C for strenuous work) but specifies no upper limit, instead directing employers to assess thermal comfort and act when staff report discomfort.
That gap is under active pressure. The Trades Union Congress (TUC) is campaigning for employers to be legally obliged to act once indoor temperatures exceed 24°C, with a proposed absolute maximum of 30°C for office work (27°C for physically demanding roles). For any organisation planning a building's services over a 10–15 year horizon, designing in headroom against tightening workplace temperature regulations UK is prudent.
What's the business cost of an overheating workplace?
The cost of inaction is now being quantified at a national scale. The UK Parliament's Environmental Audit Committee has warned that heat-related impacts – including disrupted sleep that carries into the working day – could cost the UK economy in the region of £60 billion a year, equivalent to roughly 1.5–2% of GDP, and that heatwaves could claim up to 10,000 lives annually without concerted adaptation.
For an individual organisation, the cost shows up as:
- Lost productivity – measurable declines in output and accuracy across the workforce
- Higher absenteeism – heat-related illness and fatigue
- Reputational and recruitment risk – wellbeing-conscious staff and clients increasingly notice how a building is run
- Reactive spend – emergency portable cooling hire is expensive, inefficient and rarely a long-term fix
Set against those figures, a planned investment in efficient, permanent commercial cooling solutions is straightforward to justify.
How do fan coil units cool a building?
A fan coil unit (FCU) is a compact device that draws in room air, passes it across a coil carrying chilled water, and circulates the cooled air back into the space. Reverse the principle with warm water and the same unit provides heating – making FCUs a genuine four-season climate solution rather than a summer-only bolt-on.
Crucially, FCUs are hydronic (water-based). They connect to a building's chilled-water circuit – supplied by a chiller or, increasingly, a reversible air-source heat pump – rather than to refrigerant pipework. That makes them:
- Ideal for retrofit, where a building already has a wet system or is adding a heat pump as part of decarbonisation works
- Highly controllable, zone by zone, room by room
- Compatible with low-carbon heat sources, including recovered waste heat
This combination of efficiency and flexibility is why fan coil units are a default choice for energy efficient cooling for commercial buildings.
Why choose fan coil units over traditional air conditioning?
For many commercial and public buildings, FCUs offer advantages that packaged or split air-conditioning systems struggle to match – particularly around efficiency, acoustics, controllability and integration with low-carbon plant. Biddle, manufacturing in Nuneaton for the UK specification market, offers two ranges that cover the great majority of applications.
ProAir Series
The Biddle ProAir Series is built for installation within ceiling voids and exposed applications alike. Key points for specifiers and contractors:
- Two depths (270mm and 235mm) to fit tight ceiling voids
- Cooling outputs from roughly 2kW to over 12kW per unit across the range
- Quiet, energy-efficient EC/DC motors with sound-reducing internal lining
- Factory-fitted controls from EasyIO, Distech or Johnson Controls, compatible with any major BMS protocol (BACnet, etc.)
- UK-manufactured with one of the quickest lead times on the market
Comfort Circle2 – the 360° cassette
The Biddle Comfort Circle2 cassette unit suits exposed installations in offices, retail, showrooms, reception areas, museums, banks and libraries:
- 360° circular air discharge for even, draught-free distribution
- A patented auto-adjusting discharge ring that changes angle between heating and cooling modes – using the Coanda effect to push cooled air along the ceiling rather than down onto occupants
- One CC2 90 unit cools spaces up to 200m²; the CC2 60 covers up to 100m²
- Plug-and-play controls and a smart suspension system for fast installation
- Designed to run on lower water temperatures, making it an excellent partner for heat pumps and waste-heat reuse
For a fuller comparison of where each range fits, explore Biddle's fan coil unit solutions.
What is the ROI of upgrading to efficient cooling?
Return on investment from a well-specified FCU system comes from four compounding sources:
- Recovered productivity. Even a modest improvement against the documented 35%+ losses at high temperatures pays back quickly across a full workforce
- Energy efficiency. EC motors, low-water-temperature operation and zoned control reduce running costs versus older or oversized systems – directly supporting energy efficient cooling for commercial buildings
- Asset and compliance value. A building that holds comfortable temperatures protects occupant wellbeing, supports duty-of-care obligations and future-proofs against tightening regulation
- Avoided reactive cost. Permanent cooling removes recurring emergency hire and the disruption of overheating-related downtime
Because FCUs heat as well as cool, the same capital investment works all year – improving the payback profile considerably compared with cooling-only equipment.
Which cooling solution is right for your building?
A quick orientation by scenario:
- Building already has a chilled-water system (many larger offices, schools and public buildings): FCUs drop straight in – the strongest, fastest route
- Building has wet heating only: add a chilled-water source, typically a reversible air-source heat pump, then install FCUs
- Decarbonisation or heat-pump retrofit underway: the Comfort Circle2, designed for low water temperatures, is a natural fit
- Tight ceiling voids or acoustic-sensitive spaces: the ProAir Series, with two depths and low noise ratings, is built for it
For sector-specific guidance, Biddle's public buildings and offices solutions page sets out applications in detail.
Frequently asked questions
What is the best cooling system for schools in the UK?
For most UK schools, fan coil units connected to a chilled-water source (often a reversible heat pump) offer the best balance of controllable cooling, quiet operation and year-round heating in a single system. Because they avoid refrigerant pipework, they suit phased retrofits across an estate. Biddle's ProAir and Comfort Circle2 ranges are both used in education settings.
Is there a legal maximum working temperature in the UK?
No. UK law sets no maximum workplace temperature. Employers must maintain a "reasonable" temperature under the Workplace (Health, Safety and Welfare) Regulations 1992, and the HSE recommends a minimum of 16°C (13°C for strenuous work). The TUC is campaigning for a legal duty to act above 24°C and a 30°C absolute maximum for office work.
At what temperature does workplace productivity start to drop?
Research indicates office productivity peaks around 21–22°C and begins to decline beyond roughly 23–24°C, with significant effects after about an hour of exposure. At 35°C and above, studies have measured productivity falls of 35% or more.
How do fan coil units cool a room?
A fan coil unit draws in room air, passes it over a coil carrying chilled water and circulates the cooled air back into the space. The same unit can provide heating when supplied with warm water, making it a four-season solution.
Can fan coil units connect to an existing air-conditioning circuit?
Not in the refrigerant (DX/split/VRF) sense. Fan coil units are water-based and connect to a chilled-water circuit produced by a chiller or heat pump. If a building only has DX air conditioning, a different approach is needed; if it has a wet system, FCUs integrate directly.
What is the lead time on Biddle fan coil units?
Biddle's ProAir and Comfort Circle2 ranges are UK-manufactured with one of the quickest lead times on the market – typically around three weeks on most configurations. Contact Biddle to confirm against your specific selection.
Are fan coil units energy efficient?
Yes. Modern FCUs use energy-efficient EC motors, support zoned control to avoid cooling unoccupied spaces, and can run on low water temperatures – making them well suited to heat-pump and waste-heat systems.
Keep your building ahead of the heat
UK summers are getting hotter, longer and harder to ignore – and the buildings that cope best are the ones planned now, while the issue is front of mind. Biddle's UK-manufactured fan coil units deliver dependable, energy-efficient, four-season comfort for offices, schools, retail and public buildings, with the controllability specifiers expect and lead times contractors can rely on.
See the full range and specifications: view the online brochure »
Planning a project for public buildings or offices? Explore Biddle's sector solutions »