Ten Years, Three Buildings, One Lesson: The Compounding Cost of HVAC Neglect
Photo: David Martin , CC BY-SA 2.0, via Wikimedia Commons
Every facilities manager knows that maintenance matters. Far fewer can put a credible number on exactly how much it matters — which is why the servicing budget is so often the first line item trimmed when cost reviews come around.
To illustrate the stakes, we followed three hypothetical commercial buildings through ten financial years of energy bills. They are composites, but the figures are drawn from realistic UK performance data, DESNZ commercial consumption benchmarks and typical 2024–25 unit rates of around 25p per kWh. The pattern they reveal is anything but hypothetical.
Building One: The Drifter
Our first property is a 1,200m² office block on a business park outside Reading, running an early-2000s VRF system that hasn't seen a proper service since 2019. Filters are changed when someone remembers. Refrigerant top-ups happen reactively. Coils are, in the words of one contractor's survey, "significantly fouled".
A degraded system of this age typically loses 3–5% efficiency every year through fouling, minor leaks and drift from design settings. Starting from an annual cooling and heating electricity consumption of roughly 62,000 kWh, that decay compounds. By year ten, Building One is consuming around 88,000 kWh to deliver the same comfort it once achieved with far less.
Over the decade, the cumulative excess — measured against its own year-one baseline — totals approximately £340,000 in wasted energy. Add three major reactive repairs averaging £6,500 apiece and a shortened plant replacement horizon, and the true cost of drift becomes uncomfortably clear.
Building Two: The Steady Hand
The second building, a comparable office in Manchester, tells a different story. Its system is the same age, but it receives twice-yearly servicing under a planned maintenance contract: coil cleaning, filter replacement, refrigerant checks under F-Gas obligations, airflow verification and annual controls recalibration.
Diligent maintenance doesn't halt degradation entirely, but it holds it to roughly 1% a year. Consumption creeps from 62,000 kWh to about 68,000 kWh by year ten. The cumulative excess against baseline is around £95,000 — but the comparison that matters is against Building One. The serviced building spends approximately £245,000 less over the decade, while its maintenance contract costs in the region of £28,000 across the same period.
That is a return of nearly nine to one, before accounting for avoided downtime, extended equipment life and fewer emergency call-outs.
Building Three: The Modern Zoned Installation
Our third property is a 2015-era office in Birmingham, fitted with a zoned heat pump system, individual room controls, demand-based ventilation and heat recovery. Its year-one consumption sits around 48,000 kWh — roughly 22% below the older buildings before any degradation is considered.
With a proper maintenance regime, its efficiency curve is shallow: consumption reaches only about 51,500 kWh by year ten. Cumulative spend across the decade lands near £160,000, against roughly £275,000 for Building One and £205,000 for Building Two.
The lesson is not simply that newer is better. It is that modern equipment only delivers its designed efficiency when paired with the same disciplined servicing regime that Building Two demonstrates. A neglected zoned system drifts toward the performance of a neglected old one; the technology's promise is conditional.
What the Numbers Say to the Board
Three observations emerge from the modelling.
First, energy waste compounds. A 4% annual efficiency loss sounds trivial in isolation; over ten years it represents a third of the system's original performance. Deferred maintenance is not a saving — it is an interest-free loan taken out against future bills, repaid with compounding.
Second, the serviced-versus-neglected gap dwarfs the maintenance budget. No finance director would reject a £28,000 decade-long investment that returns £245,000. But because the costs and savings appear in different budget lines — maintenance versus utilities — the trade-off is routinely obscured.
Third, the coming regulatory environment sharpens the argument. With MEES requirements tightening and corporate net-zero reporting now standard, an inefficient, poorly maintained estate is increasingly a compliance liability as well as a financial one.
Where to Begin
Facilities teams don't need a decade of data to act. A single season of sub-metered consumption, benchmarked against the building's own floor area and occupancy, will usually reveal whether a system is drifting. An F-Gas log with gaps in it is a reliable tell. So is a controls system nobody has audited since commissioning.
The three buildings in our model are fictional. The arithmetic, unfortunately for many UK estates, is not. The cheapest kilowatt-hour remains the one a well-maintained system never has to use.
