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Volume 1 of the 2021 edition deals with heat recovery in paragraphs 1.67 to 1.73. Each habitable room should have mechanical supply ventilation, with the total supply air flow distributed proportionately to the volume of each habitable room. Supply terminals should be located and directed to avoid draughts. Each wet room should have a minimum continuous extract high rate from the document's own table, and the system should be designed to avoid moist air from the wet rooms recirculating to the habitable rooms. One instruction catches people out: to avoid unintended air pathways, background ventilators should not be installed with mechanical ventilation with heat recovery. Trickle vents left in the windows undermine the system.

The 2026 edition is published but not yet operative. Its own opening page states that it takes effect on 24 March 2027 for use in England for building work not in connection with higher-risk building work, and on 24 September 2027 where it is. It changes the framing rather than the principle: its table of system types describes natural ventilation as suitable only for less airtight dwellings, while continuous mechanical extract and MVHR are shown as covering both less airtight and highly airtight dwellings, and it adds that access to MVHR filters should not require tools or removal of the unit's main front cover.

None of that is the position outside England. Scotland sets ventilation requirements in section 3 of its domestic technical handbook under the building warrant system, and Northern Ireland deals with ventilation in Part K of the Building Regulations (Northern Ireland) 2012, so the letters and the procedure both differ.

Approved Document F is unambiguous that mechanical ventilation systems must be commissioned in accordance with an approved procedure, and it publishes the paperwork itself: Appendix C contains a completion checklist and commissioning sheet which the installer should complete, in parts covering the system particulars and installer details, an installation checklist, a visual inspection and the recorded air flow measurements from each fan.

For a continuous system such as MVHR the commissioning step that matters is balancing. The document says the system should be balanced to achieve design air flow rates at each room terminal, following the fan manufacturer's instructions, and where those are not available it sets out its own method: set the fan speed to achieve the desired continuous flow, set the index terminal with its valve fully open, adjust the others to reach the required flows, and raise the fan speed if the total cannot be achieved. Measured values are then compared with the design values on the sheet.

That sheet is what you should be handed. A system that has been installed but never balanced typically delivers too much air to the rooms nearest the unit and too little to the far bedroom, which is the commonest reason an expensive installation is quietly turned down or off within two years.

The case against retrofitting MVHR into an ordinary existing house is practical rather than regulatory. The system needs a supply duct to every habitable room and an extract from every wet room, in rigid or smooth semi-rigid duct, with a unit positioned where it can be serviced. In a house with shallow floor voids, no accessible loft above the relevant rooms and finished ceilings, the route simply may not exist without boxing that nobody wants.

The performance case is the airtightness one. Approved Document F's note that heat recovery efficiency should improve as the dwelling becomes more airtight is a polite way of saying the opposite happens in a leaky house. If the fabric work has not been done, continuous mechanical extract — centralised or as individual continuously running wet-room fans — usually delivers better ventilation per pound, and the guidance treats it as suitable across dwelling types.

There is a narrower option the document allows for a specific case: where a wet room is added to an existing dwelling, a single-room heat recovery ventilator can be used, needing a core through one external wall rather than a duct network. That is a genuinely useful middle path for a new en suite or a shower room in a loft conversion.

Almost all of the cost is the duct network, not the box. What moves a quotation is the number of rooms served, the duct material and route, how many bends are needed, whether ceilings or floors have to be opened, where the unit can go and how it will be reached later, whether the intake and discharge terminals need core drilling through a masonry wall, and whether the price includes measured commissioning with the Appendix C sheet completed. A quotation without a commissioning line is not comparable with one that has it.

LokalMatch handles introductions and nothing else. Describe the house once with your postcode — how many bedrooms and wet rooms, what access there is above the ceilings, and how airtight the house is if you know — and ventilation firms working in your area get in touch. It costs homeowners nothing; pros pay for the requests they receive. LokalMatch does not install anything, does not set prices and does not vet, rank or recommend any firm, so ask each one for the design flow rates they intend to commission to.