Why MVHR matters in a low-energy home

A house is only as healthy as the air inside it, and that's often where ordinary homes fall down. The better and tighter we build, the more deliberate we have to be about ventilation, and Mechanical Ventilation with Heat Recovery (MVHR) is how we keep an airtight, well-insulated home supplied with fresh air without throwing the heat away.

It's one of the least visible parts of a low-energy house and one of the most important.

A deep retrofit kitchen by RISE Design Studio, lit by a rooflight and opening to the garden. MVHR keeps air like this fresh and filtered without losing heat, working quietly out of sight. RISE Design Studio.

The ventilation problem

Ventilation has long been the weak point in energy-efficient design. Open a window and you lose the heat you've paid for. Seal the house up and you trap moisture and pollutants. Add a noisy extractor fan and you get draughts, condensation and, before long, mould. You end up choosing between a warm house and a fresh one.

MVHR resolves that. It lets you build an airtight, insulated, high-performance house that still has a constant supply of fresh air, just in a controlled way rather than through gaps and open windows.

How it works

The principle is simple. The system continuously extracts warm, stale air from the kitchen and bathrooms and supplies fresh, filtered air to the living rooms and bedrooms. As the two streams pass each other through a heat exchanger, most of the warmth from the outgoing air, often around 90%, is handed to the incoming air. So the fresh air arrives already tempered, and very little heat is lost.

In practice that means filtered air in every room, no cold draughts and no need to crack a window open, and the energy saving built into everyday life. It runs quietly in the background, and when it's done well you barely notice it, though you do tend to notice the result: fewer allergens, steadier humidity and cleaner air.

Designed in, not bolted on

MVHR is too often treated as an afterthought, a box ticked for compliance. We design it in from the start, as part of the building rather than an addition to it. Done that way it earns its place several times over: steady thermal comfort across the house, stable indoor humidity, the removal of pollutants like VOCs and nitrogen oxides, and no need for trickle vents, window gaps or extractor fans. The result does considerably more than meet the regulations.

Why the detailing matters

There's MVHR, and there's MVHR done properly, and the difference is in the design. That means ducting sized so the air moves slowly and quietly, keeping noise below around 25 dB(A); galvanised rigid or semi-rigid ducting built to last the life of the building; attenuators and silencers placed to stop sound carrying between rooms; and airtight seals so the system delivers what was calculated. We work with engineers who model not just the airflow but the acoustics, because a quiet house is part of the point.

It works on retrofits too

This isn't only for new builds. A deep retrofit benefits just as much, whether it's a mews house behind a Bayswater terrace or a community building used by families every day. If anything, getting good air into an older, previously draughty house makes a more noticeable difference.

How the process runs

The way we would take it forward on a project:

1. We assess the project and issue a tailored estimate.
2. A specialist MVHR designer works with the rest of the team.
3. The ductwork is laid out in 2D and 3D, accounting for sound and pressure.
4. We specify units from a wide, independent range, chosen on best fit rather than brand.
5. Supply, commissioning and a proper handover finish the job.

We also service systems, since something like this should perform for the life of the building, not just on the day it's signed off.

We've designed MVHR into more than twenty projects across the UK, from deep retrofits and new-build houses to cinemas and restaurants. It's hidden in the walls and ducts, but it's one of the things that most affects how a finished building actually feels to be in. If you're planning a low-energy home or retrofit and want to get the air right, we'd be glad to talk it through.

→ Email us at architects@risedesignstudio.co.uk
→ Or call the studio on 020 3947 5886

RISE Design Studio, Architects, Interior Designers + Sustainability Experts

☉ Architecture for people and planet
☉ Trading since 2011
☉ Company reg no: 08129708
☉ VAT no: GB158316403