Trickle Vents Explained. Why and when you need them

What are trickle vents and how do you work out whether you need them? The information around trickle vents can confuse and even some door and window installers may provide the wrong information. Here you’ll find all you need to know about trickle vents, when and where you need them, and why your home benefits from them too.

trickle vents in new white windows

What are trickle vents?

Trickle Vents or trickle ventilators are a component within a window or a door, situated at the upper part of the frame. Their purpose is providing permanent ventilation into the room, even with a closed window. These vents allow a small amount of ventilation through the window at all times. They come either as permanent or a controllable version, opening and closing.

Above all, they’re designed to improve the quality of air in a room and hopefully a reduction in condensation.

Types of trickle vents available

For windows and doors, three different types of trickle vent are possible, depending on the product, the installation or the building:

  • Fitted through the window frame itself or the opening sash
  • Located on a separate frame attached to the top of the window
  • Glass units with trickle vents mounted at the top

The claimed benefits of window vents

Current Building Regulations relating to background ventilation stipulate the use of trickle vents in new-build homes and extensions. Some window and door installers don’t mention the need for these at all, irresponsibly leaving the decision to the homeowner. However the reasons for using them are convincing – and it all centres around our health.

Modern materials, energy saving and interior comfort means today, we insulate our homes better than ever. Insulation is a good thing. Owners of older and poorly insulated buildings understand heat loss through walls and roofs without insulation or old single glazed windows and doors .

Thermal comfort, energy-saving, and reducing heat loss mean better all-round comfort. However, it also means better-sealed homes resulting in air unable to escape and of poorer quality inside the room. This poor-quality air comes in several forms. CO2, candles, paint fumes, cooking and bathing and those rarely opening windows in their homes. All this adds to moisture, stale air, and having to deal with condensation.

Above all, poor air quality is known to affect general health and our homes are no exception.

Do trickle vents work?

Yes they do. They provide continuous and discreet fresh air into the rooms at all times when open.

They’re especially effective in rooms rarely used such as spare rooms. Bathrooms, kitchens, and toilets also benefit.

The fact is, the winter months mean our homes are less ventilated, and we spend more time in them. These small and unobtrusive window and door enhancements provide genuine benefits in providing controlled ventilation and fresh air into the rooms we use every day and those we dont.

controlled ventilation fresh air into habitable rooms, air flushed from the home. Fresh air provided through window vents, high tech products monitor ventilation levels for good indoor air quality. Higher levels in bathrooms and kitchen, lower setting when nobody at home. and adjusted at night avoiding musty air in the morning.

Understanding when you need them

The information around the use of trickle vents is clear from reputable installers. It’s this simple.

For new build homes and extensions

Trickle vents are required in doors and windows to new build homes or new extensions, unless there’s a suitable alternative method of ventilation meeting the current Building Regulations.

When replacing old windows and doors

If you’re replacing old windows and the outgoing windows have trickle vents, the new windows must also have trickle vents to a similar or better specification. The same applies to doors.

Ventilation for new bifolding and sliding doors

You’ll see pictures of bifolding and sliding doors in new extensions. Some fitted with trickle vents, some without. What you should also know is some products don’t even come with the facility for trickle vents even though Building Regulations call for ventilation. Yet these doors are sold and installed every day.

Our advice is ask the question and then double check the answer with a reputable organisation such as the Glass and Glazing Federation offering correct advice.

If there is an alternative method of providing ventilation meeting Building Regulations, then trickle vents aren’t needed in the doors. In most cases, however, they’re required.

Myths and comments about window ventilators

Some installers and those in the glazing trade can’t see the point of trickle vents. This article helps you understand why they’re used and the benefits of trickle ventilators in your new windows and doors. But let’s address some of the negatives you’ll hear about these essential components.

Trickle vents are unattractive

Aesthetics are subjective. So whether something is unattractive is down to the individual. What we can tell you is some installers are unaware of how slim and minimalist modern trickle vents are. A good window installer is already aware of these and sources their products from the better manufacturers and supplier, providing up-to-date products meeting today’s aesthetic requirements. Trickle vents are no exception.

With some models looking nearly invisible within a frame and also colour matched, the arguments around trickle vents being unattractive are quite weak with trickle vent products available today.

Compromised window thermal performance

Is is true, window energy efficiency and U-Values aren’t calculated with trickle vents in the test models and simulations.

This is a confusing message. Building Regulations are different for Energy Efficiency and Ventilation. The fact remains you need them in new build projects and when replacing old glazing already fitted with ventilators. Our view is the benefits of air quality in the room is important for general health and especially given how airtight we now make our homes.

Couldn’t you just open a window?

Yes you can when the weather permits it and when it’s not a security concern on ground floor windows.

Trickle vents provide ‘background’ ventilation thats consistent whilst keeping windows secure. Open windows provide ‘purge’ ventilation that’s only as effective as the time the window remains open.

Window vents let the heat out

People feel the draught and close the vent or think the room loses its heat. The purpose of trickle ventilators is providing a consistent flow of fresh air. Any cooling of the internal temperature in winter from a trickle vent is marginal.

Your room is noisier

Another potentially incorrect statement. There are trickle vents for windows and doors with soundproofing as standard.

the night vent position is where the window can be left partially open but still locked. the window though remains vulnerable.
The night vent position is where the window can be left partially open but still locked. The window though remains vulnerable.

Ventilators vs ‘night-vent’ facility on windows

You may also be misled into thinking you don’t need trickle vents as most new aluminium and PVCu windows today have what’s called ‘two stage locking’ or ‘night vent’ facility.

This involves partially opening a window vent around 10mm or more and then locking your window. This is not an alternative to ventilators in windows.

Windows on the ground floor should certainly not be left in the night vent position and the property unoccupied. The night vent facility is simply a feature enabling additional ventilation through the window without having it fully open. It is not intended to perform the role of the trickle ventilator.

  1. Whilst the window may be locked it’s not fully secure and actually more exposed to attack.
  2. This partially open facility does provide ventilation but does not work in the same efficient way.
  3. Lift and slide doors have similar functionality but not regular single or French Doors.
  4. It’s not an alternative solution to having a Building Regulations requirement for ventilators in window.


Remember, the rules regarding window ventilators are simple.  If the outgoing (old windows) have trickle vents fitted, then the incoming (new) windows must also be fitted with trickle vents.

All new build properties and extensions are required to have adequate background ventilation whether this is by window/door trickle ventilators, purge ventilation, or extraction.

If an installer is putting you off having trickle vents, do further research, especially on patio doors and windows in new extensions.