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Vents and Ventilation

The development of double glazing over the years has led to the highly energy efficient products we see on the market today. Double glazing has become integral to reducing heat loss and saving energy in the home; and with government regulations expected to tighten in the next five years, technology is advancing towards even more efficient double and triple glazed units.

As our homes become increasingly well insulated, good ventilation becomes ever more important to combat problems associated with condensation, damp and mould.

Why do you need ventilation with double glazing?

Open double glazed window

Opening windows on a regular basis should provide adequate ventilation

In older buildings single glazed windows and poorly insulated frames provided natural ventilation, while also contributing to around 25% of heat loss. Double glazing with better insulated frames not only drastically reduces heat loss, but also makes the property much more air tight.

Four people living in one property will produce around 16 pints of moisture between them per day. All of that extra moisture has to go somewhere, but with nowhere to escape in a badly ventilated home it will lead to damp air, condensation and mould growth.

Without good air flow there will be a build up of airborne contaminants, dust and germs in the home, which can lead to poor air quality and even affect the inhabitant’s health.

It is clear that the introduction of double glazing into an existing or new-build property will stifle natural ventilation; taking measures to redress the balance through other forms of ventilation is important to keep the property and the fabric of the building in good condition, and to create a good quality of fresh air within the home.


What effect does ventilation have on insulation efficiency?

Some people may be sceptical about installing excellent high quality double glazing, to increase energy efficiency and reduce heat loss, only to open trickle vents and allow heat to escape.

To calculate the effect this has on insulation efficiency is complex and must be done on an individual basis for each property; but is worth remembering that it is more expensive to heat moisture-laden air, and a poorly ventilated house will take more heating than a well ventilated house with good air flow. The energy loss in real terms may actually be less than you would imagine.


What different types of vents are available?

There are several different products on the market that can aid ventilation and can be installed along with double glazing units, to address the problem instantly. Many of the vents available can also be retro-fitted to existing double glazing units that were previously not fitted with ventilation. A few of the different options are detailed below.


Trickle vents

The most common type of ventilation applied with double glazing, trickle vents are built into the frames of double glazed windows which can usually be opened and closed by sliding a shutter.

Holes are drilled through the frame and the vent is fitted over them, which means trickle vents can easily be retro-fitted to any double glazed window. They provide a steady trickle of natural airflow as they can be opened on each window, allowing air cross-flow.

They tend not to have a great effect on the windows energy efficiency and can be closed to suit in very cold weather.

In some properties however, particularly those that suffer from damp and condensation, trickle vents may not be enough on their own to supply adequate airflow.


Vent locks

Ventilation locks can also be retro-fitted to windows, but are often fitted as standard with many double glazing units. Also known as night locks, they allow the window to be opened ajar to allow ventilation, but are locked to prevent intrusion and for child safety.

One downside compared with trickle vents, is that they do require the owner to remember to open them regularly in all rooms, which can easily be forgotten.


Natural ventilation

Simply opening the windows on a regular basis will provide any property with adequate ventilation. Developing a regime of opening the windows for at least an hour every day should sufficiently ventilate a building.

However, this is often impractical for many people, and is not viable for some properties, such as rentals where the onus would be on a tenant to maintain the routine.


Window fans

Office double glazed windows with vents

Some window vents are more suitable for office than domestic settings.

A more severe, and perhaps more commercial option, is an electronically controlled window fan like the Vent-Axia T series window fan. Designed to fit single and double glazed windows, the fans can be fitted into glass up to 32mm in thickness.

The vent can be set to open to allow natural ventilation, and the fan can be controlled via speed settings or humidity sensors to maintain the right moisture content in the air.

The trickle vent aspect of the fan is designed to meet relevant building regulations, and the sensors controlling the fan make it as energy efficient as possible by only switching on when necessary.

The fans themselves are approximately 22 centimetres square and are cut into the glass, so this option is not the most aesthetically pleasing and while they may not suit most homes, they could be the best course of action for a house which has damp or mould problems.



Double glazing has a great impact on the energy efficiency of our homes today; and one of the major reasons it is so effective is that it makes our houses much more air-tight than they have ever been previously.

Without natural airflow the very fabric of the building is at threat from damp and moisture damage, and consideration must be given to ventilation when planning replacement or new windows.

By far the most popular choice of vent used with double glazing is the trickle vent, with the majority of windows supplied with trickle vents as standard or as an optional add on. But whatever type of ventilation you choose, it is something that must be taken seriously to protect the integrity of your property and the quality of the air you breathe.

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