MVHR Ventilation
Mechanical ventilation with heat recovery — continuous fresh air that keeps most of the warmth in
Fresh air in every room without opening a window, and most of the warmth you paid for kept inside. It only works in a house that has been sealed first — so that is the first thing we measure, and sometimes the reason we say no.
See How It Works
Two drawings. Why a window is not the answer and what the system does instead, then the test that decides whether it is worth fitting at all.
*Illustrative guide figures while launch pricing is finalised — your exact numbers follow the free survey.
What We Do
MVHR continuously replaces stale, humid air with fresh air, and a heat exchanger keeps most of the warmth as it goes. Building Regulations set a floor of 73% heat recovery for the unit; what a system actually achieves depends on where it sits and how well the ducts are insulated, and we quote the tested figure for the unit we are fitting rather than a headline percentage. It is the system that makes a modern, well-insulated home genuinely pleasant to live in: no condensation, no stuffy rooms, no open windows in January. OKPW designs the duct runs into the structure and installs, balances and commissions the whole system in-house, so it runs quietly and performs as designed.
What It Is For — and What It Is Not
MVHR gives you fresh air in every room without opening a window, and keeps most of the warmth as the stale air leaves. It only works in a house that has been sealed first, which is why we measure that before we quote.
Right for your house if…
- You are doing a deep retrofit, a new build, or an airtight extension — the fabric work and the ductwork want to happen together.
- Your house has been properly sealed. Below 5 m³/(h·m²) at 50 Pa is the level at which MVHR stays worth running, and under 3 is where it works best.
- You are on a busy or polluted road and want the windows shut — with the intake sited away from the traffic and the right filter grade specified.
- Condensation and mould keep coming back on a fabric that is otherwise sound.
- You want the same fresh air in winter that you get with a window open in June, without the heating bill that goes with it.
Not what you want if…
- You want cooling. MVHR has no refrigeration circuit, so it cannot make a room cooler than it is outside. The most it can do is stop recovering heat in summer and move cooler night air through the house.
- You want it to heat the house. The air volume is far too small to carry a heating load.
- You want to save money on heating. DESNZ's own measured retrofit found no major change in running costs, and in a house that has not been sealed it will cost you more.
- Your damp is caused by a defect. A leaking gutter or failed DPC is a repair, not a ventilation problem, and we will say so before quoting.
- There is an open-flued gas fire or stove in the house. That is a life-safety assessment for Gas Safe or HETAS, not a design decision.
- It is one room. A single-room heat recovery unit or a decent extract fan is the right answer, and a fraction of the price.
A typical Victorian terrace measures around 9 m³/(h·m²) — roughly three times leakier than MVHR wants. That is the most common reason we tell someone no, and it is why we sell the airtightness test first.
Our Process
Design Survey
We assess your layout, air-tightness and moisture loads to design balanced supply and extract for every room.
Duct Design
Duct runs, terminal positions and the loft unit location planned into the structure for quiet, efficient airflow.
Installation
The MVHR unit, insulated ducting and terminals installed and integrated during first fix wherever possible.
Balancing & Handover
Airflows measured and set room by room, controls configured, and a handover covering filters and maintenance.
What's Included
- Ventilation design survey
- MVHR unit & heat exchanger
- Rigid & insulated ducting
- Filtered supply & extract terminals
- Air-flow balancing & commissioning
- Acoustic & condensation detailing
- Controls & boost settings
- Filter guidance & maintenance plan
- Building regulations compliance
What You Need to Know Before You Buy
MVHR is the service where the honest answer is most often no. Here is how we get to it.
The airtightness test comes first
DESNZ puts the ideal below 3 m³/(h·m²) at 50 Pa and the maximum for MVHR to stay energy-efficient at 5. Across 12,277 tests of GB homes the average is 8.6, terraces 9.1 and pre-1919 stock 8.9. We test before we design, and if the number is wrong we tell you what sealing would cost before you commit to the ventilation.
What the heat recovery figure really means
Building Regulations set a floor of 73% for the unit itself. That is a laboratory figure for the box. BRE has measured installed systems as low as 50% where the unit sits outside the heated envelope, and the in-use factors behind SAP halve the credited efficiency in that case. We quote the tested figure for the unit we are fitting and keep it inside the insulation.
It is not a filter unless we specify one
Approved Document F sets no filter grade at all. If clean air is the reason you want it — pollution, pollen, a main road — the grade has to be written into the specification and priced, and the filters have to be changed on schedule.
Ductwork needs planning into the structure
Rigid or semi-rigid duct, insulated where it runs outside the heated envelope, with proper radii. Flexible duct throttles the system and is the usual cause of a noisy install. In a Victorian terrace it means ceiling voids, boxing, or a route through the floor build-up — decided at design stage, not on site.
Commissioning is a legal requirement, not an extra
Every room's flow rate has to be measured and balanced against the design, on a calibrated instrument, and the results given to building control. A system that is not commissioned is not compliant, and almost never performs.
Filters are a running cost
They are consumables with a replacement interval, and a blocked filter costs you the fan energy and the airflow together. You get the location, the specification and the interval at handover — that is required, and we do it properly.
The rules change in March 2027
England's new Approved Document F takes effect on 24 March 2027, with transitionals to 2028: flexible duct falls from 1.5m to 200mm, there are new static pressure limits and duct insulation depths, 10% balance, tool-free filter access, and any system with more than 2m of duct needs submitted design calculations. We design to the new document now.
It does not make the house airtight
In DESNZ's measured case study the house came out of the MVHR install at roughly its original permeability. Sealing is separate work with a separate cost, and it is the work that decides whether the ventilation is worth having.
Figures correct at 10 August 2026, from DESNZ, BRE, Approved Documents F and L, and the GB airtightness baseline. Your own numbers come from the survey.
Why Choose OKPW
Fresh, Filtered Air
Stale, humid air out; filtered fresh air in — continuously and near-silently, all year round.
Up to 90% Heat Recovered
The warmth you have already paid for is recovered and sent back in — not blown outside.
Built In, Not Bolted On
Ducts planned into the structure during the build, so the system runs quietly and performs as designed.
Make Your Home Worth More
A free, no-obligation survey by the people who do the work — covering Putney, Wandsworth, Richmond, Kingston, Streatham and Lewisham.
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