Choosing an MVHR system – 7 important features that glossy brochures usually don’t tell you about

There is a huge variety in the quality and type of system components available on the market. We recommend to pay attention to the following, when comparing different MVHR units:

1. Choice of heat exchanger: Paul MVHR systems incorporate two different types of patented heat exchangers. The Paul plastics heat exchanger offers the highest heat recovery rates available. For larger dwellings with few occupants the enthalpy heat exchanger might be an option to avoid over-dehumifidication. Paul offers a unique material mix for best performance, hygiene and air tightness.

2. Silent operation and thermal bridge free: Our units have a solid Polystyrene core with formed air channels for minimal heat losses and noise emmissions. Unfortunately the standard test methods don’t flag up the heat transfer through the housing. Therefore the real performance of a system can vary substantially from the acclaimed heat recovey rates. We recommend to compare Passive House certified values as they reflect the real performance of the system (see A well performing system is saving energy on a continuous basis.

3. Constant volume flow fans. Gradually soiled filters and other factors will lead to imbalances in the system. This will decrease the heat recovery rate and lead to reduced ventilation. Good systems have a volume flow constant operation, which keeps the original extract and supply air flow rates.

4. Can the supply and extract rates be balanced? For the good performance of a system it is imperative that the supply and extract rates can be adjusted with the commissioning.

5. 100% Summer bypass. The Paul novus range incorporates an automated summer bypass. When internal temperatures rise above an adjustable limit, fresh air is supplied to the rooms without heat reocvery, leading to a more comfortable environment. The 100% refers to zero air leakage when heat recovery is in operation, thus optimising the performance.

6. High grade filtration. Filters protect your heat exchanger and the ducts. We recommend to use EU7/ F7 pollen filter for the intake and G4/ EU4 for the extract. Filters should have a large surface area and a tight fit.

7. Defrost pre-heater. The higher the real efficiency of a system, the more vulnerable they are to frost. Most systems rely only on a frost protection mode, which dis-balances the supply and extract air flows when there is frost outside. Unfortunately this leads to increasingly reduced efficiencies, the more the outside temperatures drop. Consequently cold air is introduced into the dwelling, leading to higher fuel bills and cold drafts, at a time when warmth is needed the most. We always recommend using a defrost pre-heater in the Scottish climate.

… And if all of this isn’t enough, our systems are engineered and manufactured in Germany. Our Paul team has over 30 years of experience and is passionate about developing and delivering market leading technology to the Passivhaus and high performance market.

For an independent comparison of Passivhaus certified MVHR systems and their annual savings compared to a dwelling without MVHR, please see following Twitter link: