Avoiding MVHR Failures: What Architects and Contractors Overlook in Early Design

MVHR systems are critical for meeting Part F ventilation requirements in new and refurbished properties. But when they fail, the cause is rarely a product fault—it’s poor early-stage planning.

From over-long duct runs and missed access panels to noise complaints and under-ventilated rooms, small design oversights can cause big issues post-handover.

In this blog, we draw on recent projects across Hampshire, Berkshire, and Surrey to highlight the most common oversights—and how main contractors and architects can prevent them by engaging MVHR specialists from the start.

The biggest oversights in early MVHR planning

Across dozens of contractor-led and architect-led projects, we see the same issues:

• Inaccessible filter locations, requiring ceiling removal for servicing
• Supply grilles placed too close to walls or light fittings
• Extracts specified in low-use rooms instead of wet zones
• No provision for condensate management in loft or plant areas
• Systems oversized due to lack of occupancy data or airtightness assumptions

These issues lead to increased complaints, reduced lifespan, and systems that fail building control post-install.

Guidance backed by regulation and real data

As outlined in Approved Document Part F, MVHR systems must be:

• Commissioned to deliver designed flow rates
• Acoustically compliant
• Easily accessible for maintenance
• Properly zoned for extract and supply

Many projects miss one or more of these due to rushed coordination or generic designs carried over from unrelated builds.

Real project examples from 2023–2024

Camberley – Detached retrofit, Q4 2023

The client’s builder had installed a single central MVHR unit in the loft. Supply runs to ground-floor bedrooms were too long, and one grille was placed behind a built-in wardrobe. We redesigned the system into two units, cut duct lengths by 60%, and repositioned grilles with the architect. Final commissioning passed with no corrections required.

Abingdon – High-end new build, Spring 2024

The original design did not include access hatches for MVHR filters. The project architect brought us in at Stage 4 to coordinate grille positions and plant space. By shifting one access zone and replacing a duct elbow with a radial manifold, we gave full access while maintaining visual symmetry. The developer avoided £4,000 in ceiling rework.

Farnham – Developer-led scheme of three homes, ongoing

MVHR layouts were duplicated from a previous site without changes. We audited the plans and flagged oversized units, poor zoning, and lack of condensate drainage. By revising the system before install, we helped the M&E team avoid service variations during the mechanical first fix.

Endorsements from professionals

“ClimateWorks gave us an MVHR design that made sense structurally, acoustically, and visually. We’ve used them again since that first project.”
— Director, Winchester-based residential architecture studio (2024)

“Their early input on a project in Reading helped us fix layout and access issues before anything hit site. Saved us days of coordination and some very awkward rework.”
— Senior Site Manager, Berkshire development firm (2023)

Design steps we take to avoid post-install issues

We support your project with:

• Grille layout drawings with clear spacing from other fittings
• Filter access checks at Stage 3, updated for ceiling build-up changes
• Duct sizing using calculated pressure drops, not assumptions
• Part F and Part L alignment to reduce compliance risk
• Guidance on acoustic attenuation at grilles and through structure

These steps reduce the chance of system complaints, tenant callbacks, and handover delays.

What contractors and architects should do early

If you’re working on a new build or large retrofit:

• Bring an MVHR specialist in no later than RIBA Stage 3
• Avoid generic specs or templates from previous jobs
• Share up-to-date plans with electrical and structural layouts
• Clarify ceiling void depths and joist spacing
• Review plant space for condensate runs and maintenance access

We can assist your team in Farnham, Reading, Winchester, and across the region with layouts, sizing, and coordination advice before first fix.

About the author

Dr. Julian Carter
Thermal Systems Expert and Technical Advisor at ClimateWorks

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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