Office Air Conditioning: The 12 kW Duty You Already Cross

Most London offices cross the statutory inspection threshold without realising it. The rule is not about the size of a unit — where one person controls more than one, regulation 17(2) treats every unit as a component of a single system. Four 5 kW splits is a 20 kW system, and a system over 12 kW must be inspected by an energy assessor at intervals not exceeding five years.

Air conditioning is the item people leave alone until it fails, and then replace in a hurry in the middle of a heatwave, at the worst prices of the year, in a building that will only let them work at weekends.

It is also carrying a legal duty that most tenants do not know they hold. Not an onerous one — but the report it produces is genuinely useful, and almost nobody reads it.

The threshold, and why you are probably over it

Approved Documents are statutory guidance to the Building Regulations 2010 for England. Compliance is judged against the Requirements in Schedule 1; the Approved Document shows one way of meeting them. Your building control body has the final word on your specific building.

The sentence that catches small offices

Regulation 17(2) is the one to read twice. The threshold is not per unit — it is per system, and a system is defined by who can control it, not by how it was bought or installed. A suite with four wall-mounted splits on one controller is not four small installations comfortably under the limit. It is one 20 kW system, and it has been inside the duty since the day it was commissioned.

The report is worth more than the compliance

Regulation 19(2) is the part that makes this useful rather than administrative. The report is not a certificate saying the plant runs. It has to assess the sizing of the system compared to the cooling requirements of the building, and advise on improvement, replacement and alternatives.

That single requirement answers the question everybody actually has:

• An oversized system short-cycles, never reaches steady state, controls humidity badly and costs more to run than the smaller one that would have worked. It usually got that way because somebody sized it from a floor area rather than a heat gain.
• An undersized system runs continuously in summer, never quite gets there, and wears out early. People blame the units. The units are doing their best.

Both show up in the sizing assessment, and both change what you should do next. If you have inherited a suite and nobody has produced a report, regulation 21 gives you three months — and the survey you are legally required to commission is also the cheapest honest opinion you will get on the plant you now own.

Repair or replace

That third option is the one worth planning around. If a fit-out is coming, the cooling decision belongs in it — and what an office fit-out costs sets out where mechanical and electrical services sit inside the rate. How we deliver commercial fit-out covers how that work runs in a building that has to keep trading, and if the plant is coming out rather than going in, what a strip-out involves covers the waste duty that comes with it — refrigerant-bearing equipment is not general waste.

What the F-gas phase-down does, and what it does not

The UK is phasing down hydrofluorocarbons by 79% by 2030, measured against average use between 2009 and 2012. Government guidance to anyone using or servicing HFC equipment is to ask their supplier about alternatives.

Read that precisely, because it is routinely oversold. The phase-down acts on supply, not on your equipment. Nothing makes a working system illegal overnight. What a shrinking supply of high global-warming-potential refrigerant does is make servicing older plant progressively more expensive and less certain — which is a planning problem rather than a compliance emergency, and it belongs in a replacement decision you were going to make anyway.

Anyone quoting you a replacement on the basis that your system is about to become unlawful is selling, not advising.

Doing it in a building that stays open

1. 01Find the last inspection report before you do anything else. Ask the landlord, the managing agent and the outgoing tenant. It tells you the plant's age, its condition and — the useful part — whether it was ever the right size for the space.
2. 02If nobody has one, start the three months. Regulation 21 is explicit where the relevant person changes and no report is handed over. Commission the inspection rather than waiting to be asked, and use it as the survey it actually is.
3. 03Open the ceiling in three places before anyone prices the work. Pipework routes, condensate falls and existing services are decided by the building. A price produced from a floor plan is an estimate of a building nobody has looked at.
4. 04Establish the goods lift and the working hours in writing. Plant arrives in pieces and the pieces have to travel a route the building controls. Out-of-hours working is a different job, not the same job at a premium.
5. 05Ask for the heat gain calculation, not a unit schedule. A schedule of equipment tells you what somebody wants to sell. A heat gain calculation tells you whether it is the right amount of cooling for your glazing, your occupancy and your equipment.
6. 06Decide whether a fit-out is coming within two years. If it is, the cooling belongs inside it. If it is not, do the work properly now rather than patching toward a project that may not happen.

Why a builder is writing this

Because the expensive part of replacing office cooling is rarely the plant. It is the ceilings, the pipework routes, the access, and the hours — the building work around the machines.

We deliver commercial fit-out in occupied and operational buildings: retail on Sloane Street, and Cat A and Cat B works inside the V&A's Europe 1600–1815 galleries, where the public were on the other side of the hoarding. In every one of them the services decisions were made by what was actually above the ceiling, not by what was on the drawing.

2VP is the builder, not a marketplace: one contract, one named project lead, and no introducer fee stacked on the build cost. If your existing system is well sized and simply needs servicing, we will say so — that is a job we do not get.

The one line to take away

Find the last inspection report. If there is not one, regulation 21 has already started your three months — and the survey you have to commission is also the best opinion you will get on whether the system you have was ever right for the building it is in.