The cookie settings on this website are set to ‘allow all cookies’. Leaving your settings to ‘allow all cookies’ means you consent to a website remembering your preferences and generally enhancing the user experience. If you prefer a website to not remember your preferences, you can change your settings at any time by changing the privacy settings of your browser.

Find out more about cookies >


The level of ventilation is critical in an energy efficient house. The air-tightness of the house can have a significant impact on the house's energy rating.

Having spent time and money heating the air in a room, the last thing you want to do is to allow that air to escape, and of course ventilation is essential to allow poisonous gases to escape in a controlled manner.

Carbon Monoxide (CO) – though you can't taste it, smell it or see it, is a highly poisonous gas and undetected it can cause death and lasting health problems. CO forms when a fuel-burning appliance has an insufficient air supply – and this applies to any fuel (gas, oil, coal, wood) and any appliance (boiler, stove, room heater, water heater).

Sufficient and efficient ventilation is paramount to safe combustion. Manufacturers have an absolute responsibility for providing accurate and verifiable air space calculations for their products.

Through-wall appliance ventilators can be independently tested by Advantica (previously known as British Gas Technologies and now GL Industrial Services) or the BRE (Building Research Establishment) and have an equivalent free area calculation as opposed to just a free area, which is simply a physical measurement and found by British Standards to be inaccurate in many instances.

HETAS - the official body recognised by the government to approve solid fuel domestic heating appliances, fuels and services - says: "It is very important to select the correct vent for the job. This means the actual air that can be provided through the vent in order to meet the requirements of Building Regulations and Standards.

"Installers should take care to ensure they are using a ventilator with an air provision based on ‘Equivalent Area’ rather than "Free Area". We are supportive of manufacturers who provide the right information with their products in order to assist our engineers in making the right choices."

Jim Lambeth, technical manager for the Solid Fuel Association said: "What is important to note is the actual air which can be transported through the vent not its physical size. Installers should take care to ensure they note the ventilator's 'Equivalent Area', sometimes also known as 'Effective Free Area', rather than simply 'Free Area' often quoted in sales literature."

An open fire and most room open gas heaters operate with a chimney of 200mm internal diameter. In the SAP calculation a 200mm diameter chimney is deemed to lose 20 cubic metres of air every hour.

The ventilation loss from a chimney with a smaller diameter is half this rate at 10cm3 and most stoves operate on a flue of 150mm internal diameter. A closed loop stove and chimney system, in which the new generation of stoves take the combustion air directly from outside the house will reduce the air loss from the room to virtually zero.

Once installed it is essential that the ventilators remain clear, however with energy prices so high there may be a temptation to block the vents to keep the house warm.

Some manufacturers, such as Rytons, ensure that their internal and external grilles are stamped with DO NOT BLOCK as a reminder to homeowners, and ventilation sets are offered with a wide range of cowls and internal baffle systems to alleviate draughts and keep the atmosphere comfortable.

The aim is to make their ventilators as unobtrusive as possible.

British Board of Agrément (BBA)

The main function of the BBA is to evaluate innovative building products and award its Agrément certificates to those that are fit for their intended purpose.

Regular manufacturing checks ensure each product is of a consistent quality for assured performance. BBA approved products are accepted by the NHBC, building control officers, architects, engineers and surveyors nationwide.

British Board of Agrément (BBA)

HETAS is the official body recognised by the government to approve solid fuel domestic heating appliances, fuels and services. Work undertaken by HETAS is varied and wide ranging from promoting and monitoring the safe installation and use of fuels and appliances to influencing legislation, regulations and policies which affect the solid fuel industry.

The Building Research Establishment (BRE)

The BRE is a world class testing authority offering an extensive range of services covering every aspect of the built environment.

The Building Research Establishment (BRE)
Advantica Technologies

Previously known as British Gas Technologies and now GL Industrial Services, developed the dynamic test procedure for calculating the equivalent area of a ventilator after it was agreed that the previous system of simple physical measurement was unreliable and inaccurate in anti-draught ventilators due to the aerodynamic characteristics of the baffle systems, and a formal standard was required for manufacturers.
Advantica Technologies

Key information provided by Rytons Building Products Ltd