MVHR - Mechanical Ventilation Heat Recovery Systems Technical Tips

12 Things you should know, note and apply to mechanical ventilation heat recovery systems (MVHR)

Heat Recovery Systems

MVHR House

1. Heat Recovery is whole house ventilation and recovers heat that would have otherwise have been lost

Heat recovery is a balanced whole house ventilation that both supply's and extracts air and recovers up to 95% of heat that would have otherwise been lost through the ventilation process. With a centrally mounted heat recovery unit located in a cupboard, loft or ceiling void, each room is connected via a ducting network and simple ceiling or wall grilles are present in each room.

Heat Recovery Ventilation is suitable for new build properties and heat recovery systems choice should be based on a calculation of floor area, number of bedrooms and occupancy levels. Regulatory rates are detailed in Part F of the Building Regulations (England and Wales)

healthy home

2. Heat Recovery Ventilation has many benefits for the home and the occupant

Whether it be about emission ratings, energy usage, health, indoor air quality or acoustics, Heat Recovery comes with many benefits;

1. Direct Reward in SAP for choosing an efficient ventilation strategy that directly reduces heating requirements to the dwelling

2. Year round removal of indoor air pollutants and elimination of risk of mould and condensation

3. A balanced ventilation system for the whole house that recovers heat that would have otherwise have been lost

4. Low noise, non-intrusive ventilation system for end users

5. A healthy, happy home!

5ach mvhr

3. Heat Recovery Ventilation works at its best in airtight properties less than 5ach

It can be installed in any new build dwelling (and refurbishment too!)

To maximise the Heat Recovery Systems performance, especially the heat exchange efficiency, it is suitable for dwellings with an air tightness levels of 5ach or below (air changes per hour)

Basically, the more sealed the dwelling, the more effective the heat recovery system will be for the home and its occupants.

If the building is leaky to begin with, the rewards of recovering the heat are minimised and somewhat lost!

Heat Recovery Filter Replacement

4. Heat Recovery filters are crucial to long term performance in the home

Every Heat Recovery system has filters that help to maintain;

1. Airflow rates as required by Building Regulations

2. Heat Exchanger efficiency (up to 95%!)

3. Consistent levels of Indoor Air Quality for occupants

Air is drawn in from outside - have you looked at a UK Air Pollution Map recently? The air that is entering the home will carry a considerable number of airborne pollutants and particles.

For home owners and occupants, filters reduce and remove these pollutants and particles from entering the home - crucial to airtight homes and those living with allergies or conditions such as asthma.

If a filter clogs then airflow performance and heat exchanger efficiencies are affected and the system won't run at its optimum. Just think about your hoover and how it doesn't pick up dirt when the filter needs changing or emptying!

Read our blog on what we found on the sunny south coast and see how we are extending our Guaranteed Installed Performance focus with the introduction of thefirst homeowner registration for Heat Recovery Units.

We've even got brand new videos for homeowners which take you through a step by step process of how to change your filters

scracthing head

5. Heat Recovery Ventilation needs controls and instructions for end users just like heating systems, washing machines and cookers! (it's the new white good on the block after all!)

What do you do to your heating system if you go on holiday or want to make an adjustment because it's a particularly warm day in February (who are we kidding?) or just want to turn it off? - The thermostat or the control panel which is usually located in the hall way or in an easy to reach location.

Heat Recovery Ventilation is fundamental to the indoor environment and given its suitability in air tight dwelling designs, it is crucial that occupants know and understand what it is and how it works as well as when it needs maintaining.

Controls need to be visible within the home in order that the end user can:

1. Understand the operating mode of the unit
2. Make necessary changes
3. Be aware when the system should be maintained e.g. filters need replacing.

New Guidance from the NHBC (National House Building Council) gives best practise on MVHR design and installation and details this new requirement for homeowner controls that are easily accessible and located within the dwelling.


6. Heat Recovery Ventilation should be treated as a system: Think Unit, Think Ducting, Think System

Heat Recovery is a whole house SYSTEM and should be treated that way throughout the design and installation process.

The Heat Recovery Unit and the Ducting choice will all impact on Guaranteed Installed Performance of the system as well as have direct impact on time and costs associated with installation.

  • You could have the UK's best performing Heat Recovery Unit BUT with a poor installation this won't ever be replicated in the installed environment - so what's the point?

  • You could have the UK's best performing Heat Recovery Unit BUT if it is suitable for a 2 bedroom property and you design it into a larger 3 bedroom house you won't be able to achieve the performance and will create a lot of noise - so what's the point?

  • You could have the UK's best performing Heat Recovery Unit BUT you use the wrong ducting, crush it and don't ensure all seals are airtight you won't achieve the performance - so what's the point? The Point is - Think Heat Recovery SYSTEM. Choose the right materials for the job to achieve Guaranteed Installed Performance.

NHBC Guidelines on Heat Recovery

7.New Heat Recovery Ventilation Best Practice Guidance has been published by the National House building Council

In a recent study undertaken by the BRE, 9/10 heat recovery units that had been installed in homes had to be re-commissioned and changes made to air inlet valves. The 10th installed unit actually had to be completely replaced as well as changes made to ducting and insulation.

As a result of the research findings and the increased focus on Guaranteed Installed Performance, the NHBC have published a Best Practice Guidance Document on Heat Recovery Ventilation which gives guidance on and new introductions on three key areas:

Heat Recovery Sizing

8.Guaranteed Installed Performance starts with design - size the unit for the house, not just the energy reward!

You wouldn't choose Ussain Bolt to run a marathon nor would you enter a Morris Minor in a Formula 1 Grand Prix Race.. would you?

So why choose a Heat Recovery system that isn't fit for purpose - or just based on it's Specific Fan Power and Heat Efficiency?
Use the pressure curves that show you how the heat recovery unit will perform as a system - WITH THE DUCTING!
Read our blog - 'With Curves in all the right places' to understand more about Heat Recovery Unit sizing

9.You need a good installer for a Heat Recovery System - eliminate any risk from the very beginning!

If is often when products get to site that things can go wrong - mistakes happen and issues start to occur.

A well designed system on paper and a well manufactured product supplied in a white box can all fall down when put together with a poor installer onsite.

The magnitude of the risk of getting it wrong is worthwhile thinking about when looking at installers. We have seen from BRE research that 10/10 homes with MVHR installed had to have some kind of call back and amendment - be it re-commissioning or total replacement. In the worst circumstances, condensate could collect on the wrong side of the unit (wrong handing) and cause catastrophic issues for the home and the occupant!

We are offering preferential rates for the two day NICEIC Domestic Ventilation Assessment in partnership with CERTSURE who are a leading building services training provider in the UK.

Click here for more information.

Vireo Kitchen Cupboard

10. Location, Location, Location - It's an important aspect of designing a Heat Recovery System and should always be considered.

A heat recovery unit can be sited in the loft, in a cupboard or even a ceiling void, however the recent Best Practice Guidance from the NHBC focuses installation of the unit within the heated envelope of the building.

Location is a design consideration and should be part of the decision making process for; NOISE, ACCESSIBILITY and PERFORMANCE.

Did you know? Compact MVHR units are now available that have been designed to fit into a standard kitchen cupboard!

11. MVHR isn't a noisy ventilation system - it's poor design, installation and the wrong unit that introduces noise!

nuisance noise

Things that are likely to introduce noise into the dwelling post installation of Heat Recovery are;

1. Under-sized Heat Recovery Unit - if it has to work harder than it should to provide airflows in a larger property it will be noisy (recommended not to run at above 60% capacity on trickle speed)

2. Wrongly located Heat Recovery Unit - placing the unit in a bedroom cupboard is not recommended!

3. Incorrect size and type of ducting - Pushing large volumes of air around the wrong diameter duct will cause noise! Work with the building and the focus on achieving optimal performance and running speeds to minimise noise.

12. There are many ducting options for Heat Recovery System Installation - all with varying performance and installation benefits as well as impacts on Guaranteed Installed Performance.

ComfoTube for Heat Recovery Ventilation

Ducting is a huge part of a Heat Recovery Ventilation System in a home - after all it carries air around the system - too and from the rooms in the dwelling.

The choice and type of ducting impacts on:

1. Pressure Handling (Velocity) and therefore airflow capacity for the dwelling size
2. Noise transfer within the dwelling
3. Cost and Time of Heat Recovery System Installation.

Considerations for ducting:
Radial v Branched System
Rigid v Semi-Rigid

Click here to find out more about Semi Rigid Ducting - the best option for Heat Recovery System Installations or click on the image below to watch our ComfoTube in action!