MVHR Design and Commissioning Standards: What UK Law Requires for New Systems

Cutting Corners on Ventilation Design Is No Longer an Option

MVHR systems are not plug-and-play devices. To work correctly and legally in the UK, they must be designed and commissioned in line with strict performance and regulatory standards.

This is where many projects fall short. Homeowners invest in insulation, double glazing, and energy efficiency—but if the ventilation system isn’t designed or commissioned correctly, the building fails to meet Part F and Part L of the Building Regulations. Worse still, the MVHR might underperform, waste energy, and cause discomfort.

In places like Wokingham, Newbury, and West London, building control officers are now more stringent than ever. Without design documentation, airflow testing, and commissioning results, your build won’t pass inspection.

Whether you’re building a new home or retrofitting a system into a renovation, proper MVHR design and commissioning is not optional. It’s required by law.

Why MVHR Needs Professional Design – Not Just Installation

Too often, MVHR units are chosen based on price or basic flow rates alone. But without a full design, systems can:

• Fail to meet airflow targets
• Be too noisy for occupants
• Create cold drafts in bedrooms
• Short-circuit airflow (extract and supply too close)
• Waste energy due to poor duct routing

A professionally designed MVHR system will:

• Calculate required airflow per room based on floor area and moisture production
• Determine the best duct routes for space and airflow efficiency
• Minimise pressure losses and noise
• Ensure all valves are accessible for maintenance
• Optimise unit location for access and thermal comfort

At ClimateWorks, we carry out all MVHR design work in-house, using your architectural plans or a site visit. Our designs are compliant with:

• Approved Document F – Ventilation
• BS 9251 – Residential ventilation standards
• CIBSE Guidelines – Airflow, acoustics, and performance in residential buildings

Commissioning: The Legal Requirement Too Many Builders Ignore

After the MVHR system is installed, commissioning must be completed before Building Control will approve the ventilation system. This involves:

• Measuring airflow from every extract and supply valve
• Comparing measured rates to the designed flow rates
• Adjusting air volumes to balance the system
• Testing the operation of boost modes and controls
• Recording fan settings and confirming performance
• Producing a signed commissioning report

This ensures the system works as intended, delivers clean air, and prevents problems such as:

• Noise complaints
• Stuffy bedrooms
• Over-extraction from wet rooms
• Inadequate filter access
• System faults or inefficiency

Without commissioning, MVHR becomes guesswork—and Building Control will not accept the installation.

Reference – GOV.UK: Ventilation Compliance Guidance

Case Study: Poor Commissioning Reversed in Wokingham Retrofit

A homeowner in Wokingham contacted us after experiencing noise issues and musty smells in their new extension. They had an MVHR system installed by a general builder, but no commissioning was ever done.

Upon inspection, we found:

• Supply ducts routed too close to extract points
• Ductwork undersized, causing noise and pressure loss
• Unit installed in a hard-to-access loft corner
• No boost function wired to bathroom switches
• Dirty filters and unbalanced airflow

We redesigned the layout, installed silencers, rewired the controls, and re-commissioned the entire system. The result: a fully functioning MVHR setup with measured airflow, no noise, and full Part F compliance.

Design Documentation Required for Compliance

Before you even begin installation, UK law requires that you produce and retain certain MVHR documentation for Building Control. This includes:

• Full layout drawings showing duct routes and valve locations
• Calculations of airflow per room
• System specification including unit type, filter grade, and controls
• Noise attenuation provisions
• Design intent document
• Final commissioning report signed by a qualified technician

This paperwork must be handed over to both the homeowner and Building Control at the end of the project.

Failure to do so can result in:

• Delay or refusal of completion certificate
• Insurance complications
• Failed SAP assessments
• Potential legal liability under the Building Act

Bullet Summary: What MVHR Design and Commissioning Must Include

• Room-by-room airflow calculations based on occupancy and size
• Duct routing plans with low resistance and minimal bends
• Unit placement for access and efficiency
• Acoustic treatment to limit noise
• Final balancing with measurement tools
• A full commissioning report for Building Control

Working with ClimateWorks: Certified MVHR Design and Install Experts

At ClimateWorks, our MVHR services go far beyond supply and install. We offer:

• Bespoke system design using CAD or architectural layouts
• Pre-install site survey and builder coordination
• Duct sizing and routing for performance and discretion
• Certified commissioning to Part F standards
• Handover packs for Building Control and homeowners

Our team works on projects across:

• Basingstoke
• Newbury
• Reading
• West London
• Wokingham
• Guildford
• Petersfield and surrounding areas

Every system we install includes full airflow verification and compliance sign-off. We also provide filter replacements, servicing, and annual performance checks post-installation.

👉 Visit our MVHR page to request your design consultation

References

[1] GOV.UK – Approved Document F: Ventilation
https://www.gov.uk/government/publications/ventilation-approved-document-f

[2] CIBSE – Domestic Ventilation Systems
https://www.cibse.org/knowledge/knowledge-items/detail?id=a0q3Y00000ICv4oQAD

[3] Building Services Compliance Guides – MHCLG
https://www.gov.uk/government/publications/building-services-compliance-guide

[4] BS 9251: Ventilation for Dwellings
British Standards Institution (access required)

Author Bio

Dr. Julian Carter is a highly experienced thermal systems expert with over 15 years in the field, holding a PhD in thermal systems. His career spans academic research, consulting, and teaching, focusing on air conditioning and refrigeration systems. Dr. Carter bridges the gap between theoretical advancements and practical applications, providing expert insights to organisations like ClimateWorks, where his guidance informs decision-making and industry best practices. Notably, he has worked on international projects with organisations such as Daikin Industries, the International Institute of Refrigeration (IIR), and the United Nations Environment Programme (UNEP). Currently a lecturer at Edinburgh University, Dr. Carter combines his expertise with a passion for educating the next generation of engineers and advancing climate control technologies.

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