50% Off Triple Glazing! View offer or request a call back!

As part of the updated Building Regulations in the UK, trickle vents are now legally mandatory for all replacement and brand new windows in order to improve ventilation and airflow around the home. Questions have been raised as to how efficient trickle vents are, and whether they are practical in terms of heat loss.

Trickle vents are not linked to heat loss, and are great for background ventilation and maintaining an energy-efficient home, and they are designed to be used without windows being open, making them safe and secure. They also prevent a home from overheating in the summer, which is important as more new build homes are designed to trap heat and lower energy bills by being more energy efficient. Data shows that in the year to September 2021, 84% of new build houses had an A or B EPC rating, compared to just 3% of older properties.[1]

What are trickle vents?

As more properties are constructed with airtight and energy-efficient designs, it’s all the more important for homeowners to open window trickle vents to ensure good ventilation and to protect the property from damp and mould.

A trickle vent fits at the top of a window, and allows fresh air from outside to slowly ‘trickle’ in and circulate naturally throughout a room.

Without trickle vents, rooms would be liked a sealed box, with no natural ventilation coming through. The potential for trickle vents to cause heat loss is a common concern, but the amount of heat that trickle vents actually allow to pass through is very minimal, and doesn’t enable a lot of heat to escape.

Trickle vents also work in conjunction with extractor fans in rooms like bathrooms and kitchens where there is excess moisture and more ventilation is needed. Trickle vents are either fitted to the window frame (known as slot vents), or fitted between the window’s glass and frame (known as glazed-in vents).

Why are they needed?

Trickle vents are important to keep fresh air flowing into a home. Dust, dirt, mould and fungus would otherwise build up due to excess moisture. Indoor air can also become stale due to chemicals, dust and particles from the items used within it, such as soft furnishings, electronic equipment, carpets and even the building itself.

In large amounts, these particles can become a health concern and cause breathing problems or allergies. With modern windows becoming more energy-efficient and well-sealed, there’s more potential for indoor pollutant levels to increase. Also, if moisture isn’t allowed to escape, it can build up and cause mould, damaging the building and occupants’ health. Trickle vents are designed to keep air flowing through a building, without losing excess heat.

How trickle vents affect the air in your home

By installing trickle vents, you are bringing fresh air into your home, without letting excess heat out. Trickle vents are not the same as opening a window, and they can remain open and working all year round, to ensure that stale air leaves your home, and fresh air comes in.

If you don’t have adequate ventilation in your home, you might start to see condensation building up. Condensation happens when small warm water droplets caused by warm air inside the home meet a cold surface, like a cool glass window. This build-up of moisture can make a house damp, encouraging mildew and mould to develop.

When temperatures drop, condensation has the potential to become much worse because of the differences in temperature inside the home and outdoors. This is why good ventilation and the use of trickle vents is important, especially in colder climates.

Pollutants and dust in the air

Pollutants, dust and particles can also build up in the indoor air inside your home, and having trickle vents can make a difference in ensuring that air is clean and well-circulated throughout the building. Effective ventilation is important for making a home a healthy environment to live in.

Polluted air and poor air quality in the home can cause problems with breathing, sore throats, lung problems, skin issues and can even affect mental health. With trickle vents installed, they provide background ventilation which allows fresh air to flow more freely in very small amounts throughout a home – even when the occupants are asleep, or away.

When used in conjunction with other ventilation methods like regularly opening windows, and using extractor fans, this helps remove contaminants from the air and introduce fresh air into the home.

Can trickle vents cause your home to lose heat?

A common question asked by homeowners is whether trickle vents cause heat loss. The short is answer is no, they don’t. They are designed to help keep the air inside your home fresh, dry and clean, and you can have them open all year round without major heat loss. Trickle vents can provide background ventilation when left open, doing their job in all weathers.

If your windows are well insulated with double glazing or triple glazing, they will be able to retain enough heat to keep the house warm, even with trickle vents still open. If your house is losing heat from its windows, it’s recommended to replace your glazing and invest in good draught-proofing.

How much heat is lost through trickle vents?

Trickle vents are designed to retain as much heat as possible, and to remove and bring in only a minimal amount of air. They are very efficient, so stale air that is being removed from the house doesn’t mix in with fresh air that is drawn from outside. The amount of air coming into the home is so small, that it will not impact your energy bill and will not contribute to heat loss.

If however your home is poorly insulated, trickle vents or not, you are likely to lose more heat. For instance, up to 35% of the heat in your home is lost through poorly insulated windows and uninsulated walls.[2] For trickle vents to work at their best, you must have good insulation throughout your property in the walls, windows, doors and floor.

What causes heat loss from windows?

Heat loss from windows occurs when the inner panes of glass in the window absorb heat from inside the home, and then transmit this heat to the cooler outside pane, in a process called conduction.

How heat is lost through windows - Homebrite

A process called convection also occurs in the glazing cavity. This is when air between the two panes of glass in a window is heated from inside the room, and then rises. The heat from this risen air transfers to the outside pane of glass via convection. The air then cools and falls, and is then re-heated from inside the room.

This happens in a cycle, which continually transfers heat from the inner pane to the outer pane, causing heat loss.

Preventing heat loss from windows

To prevent heat loss from windows, you can take the following steps:

Add thermal breaks

Having polyamide sections between the panes of glass can prevent heat from being conducted through the glazed frame.

Install curtains

Thick curtains can add an additional layer of insulation and trap heat in.

Allow more sunlight in

Open your blinds when it is sunny to allow rooms to warm up gently and make the most of natural sunlight.

Replace draughty windows

If you hold up a candle to your window frame and it flickers excessively, you have draughts that need to be addressed, as they can cause major heat loss.

Invest in double or triple glazing

Air gaps in double and triple glazing create extra layers of insulation which help to retain heat in your home.


[1] Russell Homes – A New Build Home Will Save You Money on Your Bills –  https://russellhomes.co.uk/news/a-new-build-home-will-save-you-money-on-your-bills

[2] The Green Age – Where Am I Losing Heat in My Home? https://www.thegreenage.co.uk/where-am-i-losing-heat-home/