Whole House Ventilation: Common Mistakes and how to Avoid Them

by Paul Williams – Domus Ventilation

We’ve been in the business for well over 30 years and, as you might expect, has been witness to a lot of changes over the decades, mostly driven by Building Regulations. We have moved from simple mechanical extract fans to whole-house ventilation, frequently with heat recovery. Ventilation has become more complex but also more important as our homes are built to greater air tightness standards in a drive for energy efficiency, and as we begin to realise the impact of indoor air quality on our health and well-being. Of course, the more complex ventilation systems become, the more opportunity for errors to creep in.

Here, we identify the four most common mistakes we regularly see when it comes to whole-house ventilation systems. Taking the time to understand and avoid them now, will save you a whole lot of time and expense further down the line!

Mistake 1:

Using the wrong size MVRH unit

Mechanical Ventilation with Heat Recovery (MVHR) systems, such as our own HRXE range, are becoming ever more popular, with their combination of supply and extract ventilation in one system. Using a heat exchanger, up to 95% of the heat is typically lost in waste, stale air is efficiently recovered and used to temper the fresh air drawn into the building, which is then filtered and distributed within the home.

MVHR units come in different sizes to meet different-sized properties. Choose the wrong MVHR size and you run into difficulties: either it’s too big and therefore not energy efficient, or it’s too small and not going to deliver the ventilation required under Building Regulations, but will deliver excess noise as the fan within the unit works overtime to meet demand.

Incorrect unit specification often results from a failure to take into account the ductwork; where it is going to run and how much resistance is going to be in that ducting system. This is frequently because the ducting drawings have yet to be produced. As a result, smaller, less powerful MVHR units can be incorrectly specified. The key here is to ensure the ductwork drawing is done prior to unit specification and prior to other services, such as gas and water pipes, going in as otherwise you will need to add more duct work to get around these obstacles. Domus Ventilation offers a free drawing service for our customers, so this issue can be entirely – and easily – avoided.

Ultimately, selecting an MVHR unit that is too small for the property will mean it won’t be compliant with latest Building Regulations and it won’t get signed off. This is an expensive mistake to make as the only real option is to replace the MVHR with a larger unit and hope there is the space for it. Replacing the ductwork with a larger profile alternative is certainly not an option as it’s already behind ceilings and walls.