VENTILATION OPTIONS
Banishing stale air and introducing a fresh supply is a key factor when it comes to establishing a healthy living environment. Rebecca Foster explores the myriad solutions available
Keep condesation at bay and improve indoor air quality with our guide to specifying ventilation systems
The drive to create a super-insulated, airtight house sits at the top of many self builders’ priority lists. However, good ventilation is also important, and is a vital factor in establishing a healthy living environment. “Poor air quality can lead to a multitude of issues within the home, including a high level of humidity that leads to condensation, the growth of damp and the accumulation of unpleasant smells,” says Tim Bartlett, director at CVC Direct.
Other consequences may include the build-up of potentially harmful allergens and contaminants. “When there’s not enough ventilation, pollutants such as VOCS (volatile organic compounds), formaldehydes and radon can accumulate,” says Stefan Huber, director of Paul Heat Recovery Scotland. “These can have long-term health implications, including cancer and impaired lung function.”
Removing stale air and getting a fresh supply inside can be achieved via various means. The right solution for your dwelling will depend on an array of factors, such as the nature of the building, your budget and how straightforward the setup is to operate. So, what are your options?
Conventional arrangements
For most existing homes, trickle vents, airbricks and natural solutions (opening windows and relying on leaky building fabrics) do the job. The majority of you probably have kitchens and bathrooms kitted out individual extractors, delivering a simple and cost-effective solution. Plus, of course, most builders will be familiar with these setups.
However, this route may not be ideal if you want to create a well-insulated, airtight home. “One problem is that the air change rate is uncontrolled,” says Chris Hamilton, sales director at Rega Vent. “Ventilation can end up being excessive, resulting in high heat losses.” On a basic level, deliberately creating holes in an otherwise airtight shell will compromise a highly thermally-efficient envelope. Plus, if airbricks are blocked with dirt or debris, then they may not be delivering the required levels of ventilation stipulated by Part F of Building Regulations – which are currently being re-written (updated guidelines are due imminently). “Many people assume that all our homes work in the same way as Victorian or Georgian properties. But these heritage houses were constructed with hygroscropic materials that absorb moisture and feature numerous ventilation paths from top to bottom,” says Stefan. “Modern homes are much more airtight and are usually built with nonmoisture absorbing products. Therefore, we need to plan and implement a more suitable strategy for new builds, and for when existing dwellings are upgraded.”
Controlled systems
Introducing some form of controllable whole-house setup is the go-to solution for ventilating an airtight, modern property. There are three main routes to choose from:
Mechanical ventilation and heat recovery (MVHR) As well as removing stale air from your home and drawing in a fresh supply, MVHR extracts and recycles heat from the outgoing flow, transferring warmth to the incoming stream. “The heat exchanger will recover energy otherwise lost by conventional methods, such as trickle vents and
extract fans,” says Jason Hoffman, residential branch manager at Systemair. “It will also filter the incoming supply and can have a positive effect on relative humidity and CO2 levels, ensuring a healthy indoor environment.”
A fan-powered air-handling unit positioned in the loft or plant room forms the heart of an MVHR setup. This is connected to a system of ducts and extract/supply points throughout the house. Old air is drawn out of each zone (especially bathrooms and kitchens) and passes through a heat exchanger before being released outdoors. If called for, the warmth is then introduced to the fresh flow of air that passes into each zone via the supply ducting (MVHR can also run in ventilation-only mode).
“To achieve maximum benefit, the setup should be installed in a well-insulated, tightly-sealed home,” says Christopher. “Existing buildings often have too much natural leakage to make it viable, and installation is more tricky. The average cost for a system – in a well-insulated, four-bedroom new build – is around £3,000 to £5,000.”
If you’re planning to install MVHR, it’s worth liaising with a reputable specialist supplier during the design phase of your project. “Planning the house and then thinking about the mechanical ventilation system as an afterthought isn’t ideal,” says Tim. “This often leads to arrangements that are more complicated than they need to be.”
It’s vital to work with an experienced supplier who has plenty of experience installing these setups in new homes. They’ll be able to design a configuration that’s easy to install and run, optimises performance and meets the Building Regulations. “It’s also important that the system is installed by a qualified BPEC registered installer,” says Systemair’s Jason. “Plus, it must be properly set up and commissioned to ensure it’s operating as it’s designed to. This information will be required for sign off from building control.”
Centralised mechanical extract ventilation (CMEV) This comprises a network of ducts connected to various terminals throughout the property. A central ventilation unit, usually positioned in the loft, draws up stale air from throughout the property and expels it through an outlet on the roof. “The system extracts from these rooms 24 hours a day and boosts the ventilation when humidity spikes are detected. For example, when someone is cooking or having a shower,” says Stefan from Paul Heat Recovery. “The replacement air is drawn in through background ventilators (trickle vents) in all habitable rooms.”
Like with MVHR, you’ll need to consider the layout at the design stage of your house to allow for clean runs of ducting with minimal bends. “Extract-based arrangements like MEV have an advantage over uncontrolled ventilation as they cut out draughts created by changing weather conditions,” says Stefan. However, bear in mind that the incoming flow of air will still be via trickle vents, so this might not be suitable for super airtight houses.
Decentralised MEV systems – known as DMEV – are also available. “These function with individual room fans that operate continuously at a low level to draw moisture from kitchens, bathrooms, utility areas or other wet rooms,” says Rebecca Mclean from Envirovent. “Centralised MEV systems – with the fan unit in the loft – work better in new builds as the ducting can be installed at first fix.”
MEV setups cost significantly less than MVHR systems – however, bear in mind you will miss out on that element of heat recovery that the latter arrangement offers. “For a well-insulated four-bedroom home, the outlay would be somewhere between £1,000 and £1,500,” says Rebecca. “However, the total cost is very much dependent on the size of the property and the ducting required.”
Positive input ventilation (PIV)
These systems comprise a small fan-powered unit (again usually in the loft), which draws in fresh air from outside. This is propelled through the property via a network of ducts. “Moisture-laden air is diluted, displaced and replaced to control humidity levels between 45%-60%, preventing condensation and mould growth,” says Rebecca.
As the supply is drawn in, the pressure increases and stale air is pushed out through gaps in the fabric of the house. That’s why this setup is generally better suited to older buildings with less efficient thermal envelopes.
“By diluting moisture-laden air and other contaminants within the indoor air, PIV can provide improvements in the health of asthma and allergy sufferers,” says Rebecca.