How to design a ventilation system into your build.

Mechanical ventilation and heat recovery is often a necessary component of a modern highly efficient, airtight property. As buildings have become more airtight, in some cases far surpassing Building Regulations standards, there is more of a need for whole-building systems that provide mechanical ventilation.

These are now replacing conventional methods, such as trickle vents and individual extractor fans in moist areas like kitchens and bathrooms.

Mechanical Ventilation with Heat Recovery (MVHR), which works on an integrated basis with whole-building ventilation, is a way to provide a fresh supply of air in our buildings that have been pre-warmed using recovered heat.

So how do you incorporate a ventilation system effectively into your build?

Correctly designing an MVHR system that integrates well within your new build is vital and should be considered as part of the initial design phase, if not some common problematic issues are listed below.


Services not considered in early design.

You need to think of services and duct routes right from the initial design stage. When it comes to the design of an MVHR system, this can have a major impact on how complex the ducting system is and even if one or two ventilation units are needed.


No Co-ordination with Structural Design.

Structural beams are often an obstacle in the service zone of a building. It is advantageous to coordinate the structural design right from the start with all larger services, such as ventilation ducting. Sometimes it is necessary that services penetrate through beams.


MVHR Unit in Poorly Accessible Position.

MVHR units need to be easily accessible for filter changes and maintenance. If they are positioned in tight spaces with no access path, it can become an adventure for occupants (and our engineers), as they play a game of twister to get into an appropriate place to change the filters. Also, the specified service space around the MVHR unit needs to be maintained.


Not Enough Space for Manifolds & Silencers.

Some of the ducting components need more space than others! For example, air manifolds and silencers. The MVHR unit needs to be positioned in such spaces that these items fit into the ceiling or in other service areas. It is therefore important to incorporate the joist layout into the final design drawing.


Not Enough Details in the Initial Design Drawing.

MVHR design drawings with too little detail leave an open door for misinterpretation on site. Duct diameters, silencers, type of terminals and other components should always be shown and narrated, as well as their position within the structure. It is better to obtain & send a full set of project drawings to include floorplans, sections plus elevations.

With a high number of clients choosing the exposed ductwork look for aesthetic purposes, detailed plans are crucial in the design stage of buildings in order to get this spot on!


No Regards for the Thermal Zone & Lack of Insulation.

If supply and extract ducts are positioned in spaces that are cold, the efficiency of the system will suffer. It is recommended to keep these fully within the thermal envelope. For example, under 100% of the loft insulation. Otherwise, sufficient duct insulation needs to be applied; we recommend 100mm of duct wrap or similar.

Intake ducts also need to be insulated if situated in cold spaces or eave spaces as these can heat up with solar gains thus eliminating the cooling effect of the summer bypass.


Too Long Intakes & Exhaust Ducts Within Warm Space.

Intake and exhaust ducts within the thermal envelope should be insulated with vapour proof material and kept as short as possible. The recommendation for passivhaus buildings is a max 1.5m each. Directional combination grilles help to keep these duct lengths short.


External Intake Close Above the Exhaust.

The position of the external intake and exhaust terminals can vary. Although 2m is recommended, even at 500mm distance horizontally very little cross-contamination occurs in most cases. It should, however, be avoided to place the intake close above the exhaust as the exhaust air is slightly warmer than the surrounding atmosphere (especially in frosty weather) and will rise into the intake path.


Intake Exposed to Strong Winds or Pollution.

The external intake of the MVHR system should not be situated in elevations which are exposed to strong wind or pollution. For example, gas flues or chimneys. For roof cowl vents, the prevailing wind direction should also be regarded to avoid contamination from flues or the MVHR exhaust.

How to design a ventilation system into your build can be a bigger problem during the colder months and during times of high winds. Make sure you discover the importance of ventilation in winter.


Extract Terminal Away from Source of Humidity.

We often find that the extract valves in wet rooms are positioned close to the door and not near the shower or bath. Please always consider the ventilation path to avoid short-circuiting extract ventilation.

Final Thoughts.

If the MVHR unit and the ducting system have been specified and designed correctly, this will guarantee that the systems will be compliant and efficient. It will give the building owner and occupants the best possible indoor air quality.

We hope this has given you a better understanding of how to design a ventilation system into your build and important things to consider. If you want to understand how MVHR systems work and all things ventilation, click this link to discover all!

If you’re looking for a company that offers ventilation maintenance, design and installation services across the West Midlands, London, and surrounding areas, contact Mid-Tech Services today. In the meantime, follow our journey on LinkedIn, Facebook and Instagram for more handy HVAC insights and news.