What Is Energy Auditing?

A full site energy audit for a medium-sized commercial premises costs £2,000–£8,000. The same audit, if it identifies a compressed air leak costing £8,000 per year, a heating system running outside occupied hours at a cost of £4,500 per year, and a lighting profile that hasn’t been reviewed since 2015, pays for itself in the first month of savings. Most businesses that commission a proper audit find results of this kind. Most businesses don’t commission one.

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Desktop audits vs full site audits

The terminology in energy auditing is used inconsistently in the market, so precision matters. A desktop audit — sometimes called a data audit or procurement audit — involves analysis of billing data, consumption patterns, and meter data without a site visit. It costs £500–£2,000 for a typical SME and can identify issues with tariff structure, billing errors, contract misalignment, and broad consumption anomalies visible in the data. It cannot identify equipment-specific inefficiencies, building fabric problems, or operational practices that drive above-average consumption in specific areas.

A full site audit involves a physical inspection by a qualified energy assessor — walking the premises, examining plant and equipment, reviewing controls and scheduling, assessing building fabric, and measuring or estimating consumption by end use. It produces a detailed savings opportunity report with costs, paybacks, and a recommended implementation sequence. The cost premium over a desktop audit is justified when the business has significant energy spend, complex plant, or reason to believe there are site-specific inefficiencies that data analysis alone won’t surface. For ESOS compliance purposes, a full site audit conducted by a Lead Assessor is required — a desktop audit does not satisfy the scheme’s site survey requirements.

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ESOS Phase 3: the December 2027 deadline

The Energy Savings Opportunity Scheme requires qualifying businesses — those with 250 or more employees, or with annual turnover above £44m and a balance sheet total above £38m — to complete an energy audit every four years and notify the Environment Agency of compliance. Phase 3 concluded in 2024; Phase 4 has a notification deadline of 5 December 2027. The audit must cover all significant energy uses across the organisation’s UK operations — electricity, gas, and transport fuels — over a representative 12-month period.

A qualified ESOS Lead Assessor must sign off on the compliance notification. Businesses holding current ISO 50001 certification can use their certified energy management system to satisfy ESOS without conducting a separate audit — provided the EnMS covers the same energy uses and operations. Starting data collection in 2026 for a 2027 notification is sensible planning; leaving it until 2027 compresses the assessor’s timeline and typically increases the cost.

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What a good audit report contains

The output of a site audit should include a consumption analysis breaking down energy use by fuel type, time of day, and — where sub-metering exists — by area or end use; a list of identified savings opportunities with estimated annual saving in kWh and £, implementation cost, and simple payback; a recommended implementation sequence prioritising quick wins before capital investments; and supporting evidence including data sources, calculation methodology, and assumptions.

What a good audit report does not do is list recommendations without quantification. An assessor who identifies “opportunities to reduce HVAC consumption” without specifying how much, at what cost, and with what payback is producing a narrative, not an action plan. The value of an audit is the prioritised, costed list of specific actions — not the descriptive assessment that generates it. If the report you receive doesn’t contain specific figures for each recommendation, ask for them before accepting it.

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The procurement connection

An energy audit that establishes your site’s detailed consumption profile is also the foundation for a better procurement exercise. Suppliers pricing against a well-characterised consumption profile — with accurate half-hourly data, known end-use breakdown, and a clear trajectory of post-audit reduction — can price more accurately and more competitively than those estimating from a standard commercial profile. For pass-through contracts in particular, where the supplier’s pricing depends on understanding your load shape and balancing costs, audit-quality consumption data is a direct commercial asset. Telnergy incorporates audit findings into procurement exercises as standard, translating the efficiency opportunity into the contract volume, profile, and structure for the next tender.

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FAQ

We’re not ESOS-qualifying. Is there any reason to commission an energy audit? Yes — commercial performance. An audit that identifies 15% of your energy spend as recoverable through low-cost changes produces a direct cash saving that has nothing to do with compliance. For a business spending £80,000 per year on energy, that’s £12,000. The audit pays for itself several times over in the first year alone. ESOS is the mechanism that requires large businesses to conduct audits; the cost and performance case applies equally to businesses of any size.

Our energy assessor submitted an ESOS Phase 2 notification in 2023. What do we need to do before 2027? ESOS operates on a four-year cycle. Phase 4 compliance is due by 5 December 2027. Your Lead Assessor should confirm the specific compliance date based on your Phase 3 notification. The Phase 4 audit must cover a reference period typically ending no more than 12 months before the notification deadline. Starting data collection in 2026 for a 2027 notification is sensible planning.

Can we use our half-hourly electricity data to reduce the cost of an ESOS audit? Yes, materially. Half-hourly AMR data is a core input to the ESOS evidence pack, and a site that can provide comprehensive, clean half-hourly data for the 12-month reference period significantly reduces the data collection time a Lead Assessor needs to spend on site. The audit doesn’t become a desktop exercise — site assessment is still required — but the overall audit cost is lower and the quality of the savings opportunity analysis is typically higher when detailed consumption data is available from the outset.