MEV vs MVHR

Penny Jones, Product & Marketing Manager at Domus Ventilation, looks at the strengths and weaknesses of MVHR and MEV systems. MEV vs MVHR – Making an informed decision Over the last few years we’ve done a great job of improving the energy-efficiency of new build homes, with a particular focus on sealing buildings to prevent any wasteful heat leakage. In general, this has worked remarkably well – in some cases it’s worked too well! We’ve created air-tight homes that can sometimes overheat or trap stale, humid air – along with a mixture of indoor air pollutants. What we’ve failed to do in that period of improvement is match our more efficient homes with equally efficient ventilation. Why not just open a window or two if you need ventilation? It’s a common question and definitely works as a quick fix, but in cooler or damp weather it’s not ideal, nor is it enough in the warmer summer months. That’s where continuous mechanical ventilation systems steps in. So, what’s the right system for you? To better understand what’s right for you, first you should know the strengths and weaknesses of MEV & MVHR. The Options – Continuous Mechanical Ventilation According to Building Regulations Approved Document F, for whole-house continuous mechanical ventilation systems you are looking at a choice between System 3 Continuous Mechanical Extract Ventilation (MEV) or System 4 Continuous Mechanical Ventilation with Heat Recovery (MVHR). The Breakdown – MEV Simple and efficient to install, MEV systems actively extract air from ‘wet rooms’ (kitchens, bathrooms, utility spaces) via ducting to a central ventilation unit. This then removes the stale air though an exhaust point. The systems are typically dual speed, providing low-speed continuous trickle ventilation and high-speed boost flow when needed. Replacement fresh air is drawn into the property via background ventilators located in the habitable rooms and through air leakage. Decentralised Mechanical Extract Ventilation (dMEV), a sub-set of System 3 (MEV), are an extremely cost effective and easy to install ventilation solution. They offer continuous low levels of ventilation to a single wet room, coupled with virtually silent operation. The Breakdown – MVHR MVHR systems combine supply and extract ventilation in one system - working on the principle of extracting and re-using waste heat from wet rooms. MVHR systems make use of the waste stale air by pre-warming the fresh air drawn into the building using a heat exchanger; up to 95% of waste heat can be recovered by this mechanism. The filtered, pre-warmed air is then distributed around the home, helping share the load for heating the home. MVHR systems provide effective ventilation, are energy efficient, massively help reduce the risk of condensation and cold air draughts and, with their built-in air filters, are particularly useful in more polluted urban areas. They are the champions of domestic ventilation! BUT. All those benefits do come with a naturally higher price tag than their counterparts and are considerably more complex to install and commission. Installation MEV systems are far easier to install since they require less ducting because air is being drawn only one way: out. With MVHR, there is a further set of ducting to take the air from the unit into rooms. MEV systems are easy to use – more of a fit and forget scenario than MVHR systems which require maintenance, including regular filter changes. In the case of our own CMX range of MEV systems, the optional speed and user controls enable simple operation and control for the homeowner, making them less likely to experience difficulties. Models are also available with an integral humidistat which identifies changes in humidity and automatically adjusts the air flow of the unit accordingly. So which is for me? Both MEV and MVHR systems are most suitable for new properties rather than retrofit, but MVHR systems do require a more airtight property where virtually all of the air flow can pass through the heat exchanger, if they are to perform efficiently. With inner cities obviously having higher pollution levels, MVHR systems are seen as more suitable because of the filter element, but in apartment blocks it’s often the case that only the first four floors are fitted with MVHR and the remaining with MEV as polluted air is heavier and therefore stays closer to the ground. MVHR systems are the undisputed kings of whole-house ventilation solutions, hence the recent boom in popularity of the units. However, if simple low maintenance, ultra-quiet ventilation is what you’re looking for then MEV could be the way to go. Find out more for yourself by downloading our full Domus Ventilation Specification Guide: If you’re still not sure, our experts are always available to ask. We’ve got nationwide coverage so find your local Sales Rep here and get the lowdown on MVHR and MEV.

For more information on MEV vs MVHR talk to Domus Ventilation Ltd