Trickle Vents Explained. Why and when you need them

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Nick Dardalis

Are you confused or received conflicting advice about having trickle vents installed in your new windows or doors? Here, you’ll find all you need to know about trickle vents, when and where you need them, and why your home will benefit from them.

Are trickle vents a legal requirement?

In June 2022, a new building regulation came into force called Part F 2021 Ventilation, also known as Approved Document F, which affects the installation of new and replacement doors and windows. It is mandatory for windows and doors to have trickle vents, whether going into new openings or when replacing your old windows.

The information around trickle vents is confusing; even some door and window installers may provide the wrong information.

What are trickle vents?

trickle vents in new white windows

Trickle vents or trickle ventilators, head vents, night vents, window vents, and slot vents are components within a window or a door situated at the upper part of the frame. Their purpose is to provide 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 with an opening and closing function.

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

Types of trickle vents

For windows and doors, three different types of trickle vents 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
  • Mounted at the top of glass units

The claimed benefits of trickle vents

Current building regulations relating to background ventilation stipulate the installation of trickle vents. Still, some window and door installers don’t mention the need for these at all, irresponsibly leaving the negative outcome to the homeowner. The reasons for using them are convincing – and they all centre around our health and reducing moisture in your home.

Modern materials, energy-saving and interior comfort mean that today, we insulate our homes better than ever. Insulation is a good thing. Owners of older and poorly insulated buildings have heat loss through uninsulated walls and roof and single-glazed windows and doors.

Energy-saving through heat loss means better all-around thermal comfort. However, it also means better-sealed homes, resulting in the air being unable to escape and poorer air quality in the room. This poor-quality air comes from several sources, such as CO2, candles, paint fumes, cooking, bathrooms, and rarely opening windows. It all adds up to extra moisture, stale air, and condensation. Above all, poor air quality is known to have a negative impact on our general health and home.

Do trickle vents work?

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

They’re particularly beneficial in bathrooms, kitchens and cloakrooms and especially effective in rooms rarely used, such as spare rooms. The fact is, the winter months mean our homes are less ventilated, we spend more time in them and we often dry our clothes indoors.

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 don’t. Keep your trickle vents open and they should help reduce moisture and freshen stale air – they really do work. Our advice is to leave them fully open at all times.

Understanding when you need trickle vents

The information around the use of trickle vents should be 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.

Trickle vents for new bifolding and sliding doors

trickle vents in a grey set of bifold doors
Discreet and effective. A neat trickle vent in the head of Schuco bifolds above the middle panel

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.

There should be no issue with most of the bifolding and sliding door brands on the market having trickle vents. Some use an additional aluminium profile at the head, other brands are able to house the vent in the existing frame, without an add-on. 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.

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.

Trickle vents and condensation

The presence of condensation inside double-glazed windows on the room side is not a fault. Condensation on the inside of your windows can come from cooking, drying laundry inside, heating, cooking, showering and even moisture when breathing. Water vapour turns into a liquid and settles on the cold surface – in this case, the glass on windows.

Trickle vents can help reduce the condensation in your home by, when open, ensuring a steady flow of fresh air into your room

6 myths and confusion about window and door trickle vents

Some installers and those in the glazing trade can’t see the point of trickle vents. Their opinion is just that – an opinion. If any installer is telling you you don’t need them, not to bother, the Building Regulations are rubbish or anything whatsoever suggesting your new windows shouldn’t have trickle vents, they are giving you the wrong advice.

This article will help you understand why they’re used and the benefits of trickle vents 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 better manufacturers and suppliers, 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

It is true, window energy efficiency and U-Values aren’t calculated with trickle vents in the test models and simulations. But neither are bay windows or specific configurations and yet we still buy these.

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 that’s consistent whilst keeping windows secure. Open windows provide ‘purge’ ventilation that’s only as effective as the time the window remains open. And if you leave your home to go on holiday, trickle vents are a benefit in keeping the home fresh.

Trickle 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. Keep your trickle vents open.

Your room is noisier

Another potentially incorrect statement. There are trickle vents for windows and doors with soundproofing as standard. A good installer should have the knowledge and ability to source these.

You simply don’t like trickle vents

Unless it is a listed building or in a conservation area, trickle vents are a legal requirement under the revised Building Regulations.

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.

Trickle vents 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.

Can trickle vents be fitted to existing windows?

Fitting trickle vents after the installation can be tricky as there are several factors to consider, but our advice here is as follows.

Your local window and door company probably doesn’t want to get involved with windows they’ve not sold or fitted. Our suggestion is to do a local search for a local double glazing repair and maintenance company.  They are more likely to have come across this type of work and help you better.

Bear in mind new windows with trickle vents are designed around these and many need an additional profile at the head to accommodate the trickle vent. So it may not be possible to fit these if the top of your frame is too narrow. It might be possible to source a slim trickle vent for the head.

Remember when windows are made with trickle vents, holes are made in the frame to create the passageway in your windows for airflow. This is a professional job done on machining centres and can’t be done in situ. To get over this, many installers get over this in situ, by drilling a series of holes instead. This is normal and unavoidable. They’re hidden by the inside and outside housings of the vent.

Part F Building Regulations and trickle vents

From 15th June 2022, any newly installed windows and doors must be fitted with trickle vents. This is to do with Part F of the Building Regulations. Meeting Part F of the Building Regulations is not new – it’s actually been a requirement since 2010 and had the last update on the 15th June 2022.

The reason for improving building ventilation, and why Part F matters, is that modern windows and doors with today’s building methods and materials make our homes better insulated and consume less energy than ever before. The downside to this improved thermal comfort is that air quality suffers.

These new requirements require ventilation in windows and doors, helping to extract excess moisture and contaminated air, especially in kitchens or bathrooms. The airflow into the room must be refreshed with new airflow – precisely what trickle vents are designed to do. At the same time, they must help keep noise levels down, which modern trickle ventilation products also do.

As these requirements have changed recently, it is very important that you check with your installer to ensure that they are fitting products that comply with the new rules.

Trickle vents conclusion

Remember, the rules regarding window ventilators are simple.  All windows whether they are replacing old ones or for a newly built opening, now need trickle vents fitted.

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

If an installer is putting you off having trickle vents, bearing in mind they’re required by Building Regulations, this should be a warning sign as to whether that installer is right for you. Get in touch with us at ATS for advice and details of installation companies that can help with your glazing and ventilation requirements.