MEP Commissioning and Testing at Practical Completion: A Homeowner's Guide

Introduction

Commissioning and testing of the mechanical, electrical and plumbing (MEP) systems installed in a new extension or renovation is one of the most important — and often most poorly documented — aspects of project completion. A new kitchen extension may contain a new heating system, underfloor heating, domestic hot water cylinder, MVHR ventilation, electrical board upgrade, and EV charging point — all of which require testing, adjusting, and certifying before practical completion is achieved. Understanding what commissioning involves and what documents you should receive helps ensure that your completed building works properly and that you can comply with future maintenance and warranty obligations.

What Is Commissioning?

Commissioning is the process of bringing installed systems to their design operating condition — testing that they work, adjusting settings to achieve design parameters, and demonstrating to the building owner that the systems are operating as intended. Commissioning is more than simple installation testing — it involves measuring actual performance against design targets (flow rates, temperatures, air volumes, lux levels etc.) and adjusting where required.

Key MEP Systems Requiring Commissioning

Heating and Hot Water System

Commissioning of a new or upgraded heating system includes:

• System flushing and cleaning (to remove debris from new pipework)
• System filling and pressurisation check
• Boiler or heat pump start-up and adjustment to design flow temperature
• Balancing radiator or underfloor heating zones to achieve even heat distribution
• Hot water cylinder thermostat setting (minimum 60°C to prevent Legionella)
• Inhibitor addition and recording for future maintenance
• Controls setup and programming — demonstrating thermostat and zone control operation to the occupant

Underfloor Heating

Underfloor heating (wet or electric) requires commissioning records including flow rates per zone, pipe circuit lengths, thermostat settings, and — for electric UFH — electrical continuity and insulation resistance tests. The screed or floor curing programme must also be followed (typically a gradual temperature ramp-up over 7–14 days to prevent cracking).

Ventilation and MVHR

MVHR (mechanical ventilation with heat recovery) systems require airflow balancing — the design airflows to each room are measured and adjusted to match design targets. Commissioning records include measured supply and extract flow rates at each terminal. For Part F compliance, these records demonstrate that minimum ventilation rates are achieved.

Electrical Installation

Electrical commissioning includes:

• Electrical Installation Condition Report (EICR) or Installation Certificate from the contractor
• Testing of all circuits (continuity, insulation resistance, earth fault loop impedance)
• RCD operation test
• Part P Building Regulations notification certificate (Electrical Installation Certificate)

Water and Drainage

• Water pipe pressure test before backfilling or covering
• Drainage CCTV survey (for new drainage connections — Thames Water may require this)
• Cold water system chlorination and flush
• Legionella risk assessment for any new hot water storage systems

Documentation to Receive at Completion

At practical completion, the following MEP documentation should be handed over to the homeowner:

• As-built drawings for all MEP services (showing actual installed routes, not just design intent)
• Operating and maintenance manuals for all installed equipment — boiler, hot water cylinder, MVHR, electrical consumer unit, EV charger, etc.
• Electrical Installation Certificate (Part P)
• Gas Safe certificate for any new gas works
• HVAC commissioning records (airflow measurements)
• Heating system commissioning record
• Manufacturer's warranties for all installed equipment
• Test certificates for drainage, water supply pressure tests

These documents form part of the Health and Safety File that the Principal Designer is required to prepare and hand over at practical completion.

The Practical Completion Inspection and MEP

The architect carrying out the pre-completion inspection should check that MEP commissioning has been completed and that all certification has been provided. It is not acceptable to issue the Practical Completion Certificate until the MEP systems have been commissioned and the documentation is in order. The architect should verify that the homeowner has been shown how to operate all systems, particularly heating controls and ventilation systems, before practical completion is certified.

Conclusion

MEP commissioning and documentation is the element of project completion that homeowners are most likely to overlook — focused on the visual finish and the snagging list rather than the mechanical and electrical systems that will determine how comfortable and efficient the building is to live in. Ensuring that commissioning is completed, records are received, and the operation of all systems is demonstrated and understood before practical completion is signed off is one of the most valuable things a homeowner can insist upon as the project approaches its end.