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Mechanical ventilation with heat recovery

Modern homes have greatly reduced levels of unwanted ventilation which reduces heat loss and improves energy efficiency. A well designed mechanical ventilation system can provide the right amount of clean, fresh air that is vital for the health and wellbeing of a household. 

Having adequate ventilation in your home is important for good health. It removes moisture and stale air along with odours and pollutants and replaces them with fresh air to breathe.

Usually, ventilation is achieved by simply opening windows and doors (known as ‘natural’ or ‘passive’ ventilation) and by using extractor fans in steamy rooms such as kitchens and bathrooms. Although this works well, it can account for around one third of space heating energy demand in an average home as a lot of warm air flows outside.

Draughts create a similar problem. While they serve to ventilate a home, they are a major source of heat loss and can make rooms feel uncomfortably chilly. 

Modern energy efficient homes are more airtight (less draughty) than older buildings because they have to follow  specifications for air-tightness in the Building Regulations. Because of this modern homes are sometimes fitted with Mechanical Ventilation with Heat Recovery (MVHR) systems also known as ‘whole house ventilation’ systems.

How do they work?

Whole-house MVHR systems extract warm, damp air from the home and draw in fresh air from the outside. The warm, extracted air is passed through a heat exchanger to recover the heat before being expelled outside. The cool, fresh outside air is also passed through the heat exchanger, without coming into direct contact with the pollutant air where it is pre-warmed before being pumped in to the property.

These systems tend to comprise of concealed ducting in ceiling voids leading to the heat exchanger unit in a cupboard or utility room (the loft is not recommended). Some units have an automatic or manual boost setting which can be used when generating excessive moisture whilst cooking or using the bathroom. Air filtration is commonly built into MVHR systems to prevent pollen and other particles from entering the home which then provides a more comfortable environment for allergy sufferers. Systems typically run continually at 80% efficiency and are inaudible during normal use.

Cost and savings

MVHR systems do require servicing as all equipment such as filters and fans must be kept clean to ensure effective operation. MVHR systems start from around £3,000 but could cost well over £10,000, depending on the size and type of the system. It can be difficult to to retrofit MVHR because of the space needed for ducting and the unit, as well as the challenge of achieving the level of airtightness needed for MVHR to work effectively.

Because the fresh air is pre-warmed, heat loss from ventilation is largely avoided. This means the householder can spend less on heating their property, reducing costs by around 25%, therefore saving money and ensuring a healthy, well ventilated home.

Frequently asked questions

I have no outside space to dry my clothes what can I do?

Drying clothes indoors can make problems with condensation and damp on the walls much worse. If you have no outside washing line or rotary hanger to dry clothes on consider using a local laundrette for drying. If you are a council or housing association tenant then your housing provider may well have local laundry facilities for you to use. Some manufacturers now make clothes hangers suitable for fitting to the sides of buildings which might be an option if you have no garden. If you absolutely must dry clothes indoors never hang wet clothes directly on the radiator. Use a clothes airer placed near a radiator in a room where you can leave a window open to allow the moisture to escape. It is also important to keep the door shut in any room where you are drying clothes to stop the mositure getting into other rooms in your home.

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Can I stop the mould coming back once I've cleaned the walls?

There are a number of prodcuts you can use to clean mould caused by condensation from your walls. Look for a cleaning product that is fungicidal and follow the instructions to slow down the rate at which mould will grow back. If you need to redecorate you can buy special paint for rooms such as kitchens and bathrooms where excessive moisture is produced. This paint generally has a 'silk', slightly shiny finish and is tough, moisture resistant and easy to wipe clean.

Need more help?

We can advise you about saving energy, or help you understand what grants and support you're eligible for:

Contact us Or freephone: 0800 082 2234

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For more domestic energy advice, view all our advice pages.

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