An office energy bill is one of the more predictable lines on an SME ledger, and one of the most useful to benchmark, because the published CIBSE TM46 office reference values give a defensible per-square-metre comparison. The bill itself is dominated by HVAC, lighting and small power, with server and comms loads usually a smaller share than office managers assume. Hybrid working has materially changed the per-employee picture without always changing the per-square-metre picture.
TL;DR
- CIBSE TM46 reference values place a typical UK air-conditioned office between defined published kWh per square metre per year ranges for electricity and fossil thermal use.
- HVAC typically accounts for around 40 to 50 per cent of an office's total energy use; lighting and small power add another 30 to 40 per cent.
- Hybrid working has reduced per-employee kWh on most sites, but per-square-metre figures often barely move because the building's base load runs regardless of occupancy.
- Standing charges on a small office electricity supply can sit between 50p and 80p per day, often 15 to 25 per cent of the total bill for a low-consumption site.
- Half-hourly metered offices above the 100 kW threshold attract capacity charges restructured under Ofgem's targeted charging review since 2022.
Last reviewed: May 2026
CIBSE TM46 office reference values
CIBSE TM46 is the standard UK published source for non-domestic building energy benchmarks, and it includes separate office categories distinguishing naturally ventilated offices from air-conditioned offices. TM46 reference values place a typical UK air-conditioned office between defined published kWh per square metre per year figures, with the air-conditioned category sitting materially higher than the naturally ventilated category. The exact reference figures are set out in the TM46 document and should be read from the source rather than from any single secondary citation.
The reference values are designed for benchmarking actual annual use against a published expected level for that building type. They are not standards or caps.
The DESNZ non-domestic energy use survey work, building on legacy BEIS publications, sits alongside TM46 and broadly confirms the office category ranges at the UK aggregate level.
Where the office bill actually goes
The internal split of an office bill varies with building type, but the general shape is consistent in the published literature. HVAC, which combines heating, cooling and ventilation, typically accounts for around 40 to 50 per cent of total energy use. Lighting and small power, which together cover the lighting array and the desk-level equipment such as monitors, laptops, phones and printers, account for another 30 to 40 per cent. Server and comms load, including in-building IT cabinets and switching gear, makes up the remainder.
The HVAC share is higher in air-conditioned offices than in naturally ventilated ones, which is part of why the TM46 air-conditioned reference figure sits well above the naturally ventilated figure.
The catch is that the HVAC share is the hardest one to reduce in occupied periods. Lighting and small power can be addressed through scheduling and LED retrofit; HVAC reduction usually requires control system changes or fabric upgrades that are slower to land.
Heating and cooling load
UK offices in 2026 carry a mix of heating sources. Gas boilers serving wet radiator systems remain the most common heating route in older stock, with electric panel heating in smaller premises and air-source heat pump systems increasingly specified in new commercial fitouts. Cooling is typically electrically driven across all building types, either through split air-conditioning units, variable refrigerant flow systems or chilled water plant in larger buildings.
The seasonal swing in HVAC load is significant. A typical office can use materially more energy per week in January and July than in April and October, with the shoulder months running at lower base demand.
Half-hourly metered offices can identify cooling load directly from the summer afternoon profile, which spikes sharply on hot days and drops back to base in the evening.
Hybrid working and the per-employee shift
Hybrid working has changed the per-employee energy denominator significantly since 2021. An office with 40 staff and three-day-a-week average attendance has roughly 60 per cent of the daily occupancy of the same office under five-day full attendance. Per-employee kWh metrics have fallen accordingly.
The per-square-metre metric has often barely moved. The base building load, including baseline HVAC setpoints, security lighting, server room cooling and standby small power, runs regardless of how many desks are occupied. A half-empty office can use almost as much energy as a fully occupied one if the controls are not adjusted to reflect actual occupancy.
In practice this is where most office energy reviews now uncover the biggest opportunities. Sensor-based controls cut lighting and small-power load on a per-zone basis when occupancy drops below threshold. Automated lighting zoning aligned to badge-in data prevents the entire floor lighting on the arrival of a single early starter. Hot-desk consolidation onto a single floor with the rest of the building set back to overnight mode collapses the active footprint to match the actual headcount. HVAC setpoint scheduling tied to occupancy patterns rather than to a static calendar saves materially on shoulder months. Building management system retrofits where the original BMS is older than around ten years often pay back faster than a unit-rate procurement exercise. None of these moves require new tariff negotiation; all of them reduce the kWh on the next bill regardless of supplier.
Lighting and small power
LED conversion is largely complete across UK office stock by 2026, but the depth of conversion varies. A site that has converted ceiling lighting to LED but kept fluorescent tube fittings in stairwells, plant rooms or undercroft car parks still carries a meaningful legacy load. Lighting controls also vary widely; sites with absence detection on every space have a different consumption profile from sites running scheduled timers only.
Small power is harder to address because each individual device draws little energy. The aggregate matters. A 40-desk office with 80 monitors, 40 laptops, 5 multifunction printers, kitchen white goods and miscellaneous chargers can carry a daytime small-power baseload measured in single-digit kW that runs five days a week.
Standby power is a particular issue overnight and at weekends. Monitors, printers and small kitchen appliances left on rather than fully off contribute to a continuous low-level draw that shows up as a non-zero overnight profile on a half-hourly meter.
Standing charges and small-site economics
For a small office on a profile class 03 or 04 electricity supply, the standing charge typically sits between 50p and 80p per day. Multiplied across 365 days that is roughly 180 to 290 pounds per year before any consumption is billed. For a site with annual electricity use of, say, 15,000 kWh, that standing charge can represent 15 to 25 per cent of the total bill.
Gas standing charges add a further fixed component, typically 30 to 50p per day for non-domestic supplies, which for a small office can total around 110 to 180 pounds per year.
The lowest unit rate does not always produce the lowest bill on a small office supply. The combination of standing charge and unit rate has to be modelled against the site's actual annual consumption.
Half-hourly metered offices and capacity charges
Larger offices crossing the 100 kW threshold operate on half-hourly metering. Half-hourly metered offices are billed on capacity and Distribution Use of System charges as well as on unit-rate consumption. Ofgem's targeted charging review, which moved more network cost recovery onto fixed charges from 2022 onwards, has restructured how these charges fall on different site types.
An office that has substantially reduced peak demand since 2019 through equipment efficiency, lighting upgrades and hybrid working may still be carrying an agreed import capacity that reflects the old peak. Capacity charges apply to the agreed capacity, not the actual peak, and a formal capacity reduction request to the distribution network operator can be made where headroom is genuinely unused.
The DESNZ March 2026 statistical release on non-domestic prices reports continued upward pressure on the fixed-charge components relative to the variable unit rate, which makes capacity reviews more material in 2026 than they were in 2020.
Office energy split, an indicative table
| End use | Typical share of total office energy | Typical reduction levers |
|---|---|---|
| HVAC (heating, cooling, ventilation) | Around 40 to 50 per cent | Controls, setpoint scheduling, plant upgrade |
| Lighting | Around 15 to 20 per cent | LED depth conversion, absence detection, zoning |
| Small power and equipment | Around 15 to 20 per cent | Standby control, hot-desk consolidation |
| Server and comms | Around 5 to 15 per cent | Cabinet rationalisation, cloud migration where applicable |
| Other (lifts, kitchen, hot water) | Remainder | Schedule and demand-led control |
Ranges drawn from CIBSE TM46 references and Energy Saving Trust office sector publications. Site-level variation is significant.
Regional and building-type variables
Distribution Use of System charges differ across the 14 GB electricity distribution regions, so an air-conditioned office in the Eastern distribution region and an equivalent office in the South West face different standing charges and different unit-rate adders on the same supplier tariff. Gas transmission charges differ between the Northern and Southern zones in a similar way.
Building age and fabric matter at least as much as supplier choice. A 1960s air-conditioned office with single-glazed sections and limited fabric insulation will consume more per square metre than a 2010s air-conditioned office with high-performance glazing and tighter envelope, even on identical occupancy and equipment specifications.
Devolved regulatory differences in Northern Ireland sit alongside the GB regime; offices in Belfast are billed under the UREGNI framework rather than Ofgem.
Putting the benchmark to work
The practical office benchmarking exercise has three steps. Establish the building's gross internal floor area in square metres. Pull the last 12 months of total electricity and gas consumption in kWh from the supplier billing data. Divide each by the floor area to get kWh per square metre per year for electricity and for fossil thermal. Compare against the TM46 office reference values for the appropriate office subcategory.
A small SME office sitting well above the TM46 reference range for its subcategory has a reasonable expectation of finding meaningful reduction opportunity. A site sitting close to or below the reference range has less headroom and should look harder at procurement, capacity rating, and standing charge structure rather than at consumption reduction alone.
Here is where it breaks for many small offices: the benchmarking exercise itself is rarely run because the floor area is not easily to hand. A site with a current lease should be able to confirm net internal area from the lease schedule.
The benchmarking exercise costs nothing beyond the time to pull the numbers, and it puts the supplier conversation onto a footing the supplier rarely volunteers.
Editorial disclaimer. KaelTripton is an independent UK publisher. This article is editorial, not personal financial or energy procurement advice. Rates, caps, grant levels and supplier offers move; verify any figure with the named primary source before acting on it. KaelTripton does not earn commission from suppliers or brokers mentioned.
Frequently asked questions
Which UK reference source covers office energy benchmarks?
CIBSE TM46 is the standard published reference, with separate categories for naturally ventilated and air-conditioned offices. DESNZ non-domestic energy use surveys provide complementary aggregate data.
What share of an office bill is HVAC?
Around 40 to 50 per cent of total energy use is typical, with the share higher in air-conditioned offices than in naturally ventilated ones.
Has hybrid working reduced office energy use?
Per-employee energy use has fallen materially. Per-square-metre use has often barely moved because the building base load runs regardless of how many desks are occupied.
What is the standing charge on a small office electricity supply?
Typically between 50p and 80p per day in 2026, depending on supplier and distribution region. Across a year this totals roughly 180 to 290 pounds before any consumption is billed.
What is a capacity charge?
A charge linked to the maximum agreed import capacity at the supply point, applicable to half-hourly metered sites. It applies whether the capacity is fully used or not.
Can an office have its agreed import capacity reduced?
Yes, by formal request to the distribution network operator, where actual peak demand is materially below the agreed capacity. The change does not happen automatically.
Sources
- CIBSE - TM46 energy benchmarks for non-domestic buildings, office categories (referenced May 2026)
- Energy Saving Trust - office sector energy guidance (referenced May 2026)
- DESNZ - non-domestic energy prices statistics, March 2026 release
- DESNZ - non-domestic energy use surveys (legacy BEIS publications, accessed May 2026)
- Ofgem - targeted charging review and Distribution Use of System reforms (2022 to 2026)
- Ofgem - energy advice for businesses, half-hourly metering rules (May 2026)