MVHR is the best investment you can make in terms of health, comfort, and energy conservation. There are now lots of providers to choose from, all claiming theirs is the best solution, and at first glance most appear to charge less than we do, so we expect you shop around and check their reviews. To help you prepare your specification ahead of the tender process, feel free to refer to any of the points below. Mention you’re planning to have the installed system independently verified too, before you settle their bill.
Part-F sets a maximum noise limit of 30dB(A) for noise-sensitive rooms (e.g. bedrooms and living rooms). This is equivalent to a whisper. Passivhaus compliance is a little over half this volume, so practically imperceptible. Noise issues are normally caused by air turbulence from poor ducting design or installation, or from under-specified units thrashing to meet the mandatory flow rates. Vibrational sound transfer from the machine itself should also be mitigated. Acoustic design and measurement is our specialty.
Part-L1 states the installed MVHR should consume under 1.5 W/l/s during normal operation. This is easy to test but difficult to fix after installation. Excessive energy consumption is normally caused by poor duct design, leakage in the duct system, convoluted ducting with too many bends, or an under-specified machine. To meet ‘manufacturers requirements’, also a requirement of Part-F, the machine should be able to deliver your normal ventilation rate while running at 30-50% of its maximum duty capacity. Energy efficient design is also our specialty.
Part-A regulations mean you can’t drill holes anywhere you like. If holes are needed in joists, steels, load bearing walls, or other structural elements, a structural engineer should confirm the integrity of the building is not adversely affected BEFORE installation. Besides designing in 3D, the designer may need to speak to your structural engineer, frame builder, steel fabricator, Passivhaus designers or building control. This is not a problem you want to discover on site.
Part-O regulations may require TM59 thermal modelling to prove your property will not overheat. If you’re planning large South or West facing windows or roof lanterns, you would be very wise to consider overheating risks before finishing the building design or ordering glazing. Solving overheating issues can affect the window, insulation and ventilation design. Your MVHR may need to deliver elevated flow rates without becoming noisy. That additional capacity may require more room for plant and ducting, and that might not be available later. Active cooling through MVHR requires a lot more capacity. Your MVHR designer should help you assess and then mitigate the risks. Don’t rely on the ‘simplified assessment’ included with the SAP calcs.
Installing MVHR doesn’t mean you automatically comply with ADF(1) regulations (i.e. Part-F). Besides setting mandatory air flow rates for both wet rooms and (now) habitable rooms, ADF(1) compliance requires purge ventilation for ALL habitable rooms, i.e. bedrooms and living spaces. This requirement is normally met by installing openable windows with the correct size aperture, but if you can’t do that for noise, security, safety, or air quality reasons, the purge ventilation must be met by ‘mechanical means’. For MVHR that means potentially delivering ten times more air to certain rooms and extracting the same. Mechanical purge is very different from the normal boost function, which might only deliver slightly more than normal.
Part-B regulations require fire and smoke protection measures if your ducting penetrates a floor or other fire resistant layer. You may need a combination of snap-shut intumescent air valves, fire collars, or motorised dampers potentially connected to your fire alarm. The MVHR designer is not responsible for fire safety, but they should certainly assist the person who is by recommending appropriate measures, and then locating them in a suitable location for routine inspection and maintenance.
“Those who procure, plan, manage and undertake building work of ANY kind” according to the revised Building Safety Act of 2022. The person for whom the work is being done (often the developer or building owner) must take all reasonable steps to ensure those they employ to work on a project are competent to do that work, and that all building and design work complies with all relevant building regulations. Competence and compliance both need evidencing. In short, you are ultimately responsible.
