Although boilers are an essential part of our homes, more people are choosing to tuck them away into smaller spaces.

Recent research undertaken by npower showed that more than half of people (57 per cent) would want to knock £5,000 off the asking price of a property if it had an exposed boiler. That amount is more than the typical cost of a new heating appliance. The research also showed that 68 per cent of Brits would be put off buying a property if the boiler was uncovered.

Hiding a boiler is now easier than ever, as there are some types on the market that can fit into standard kitchen cupboards. But if you have a boiler installed in a cupboard or enclosed space, what kind of ventilation is required?

Although the boiler itself doesn’t require ventilation, the waste gases produced by the boiler need somewhere to go. They are normally expelled via a flue that leads outside. But what are the regulations when it comes to boiler positioning and flue ventilation?

What are the regulations of having a boiler cupboard?

If your boiler is positioned inside a cupboard, there are some clearancing rules to adhere to. There should be a gap of 300 mm between the top of the boiler and the top of the cupboard. There should also be a gap of 100 mm between the bottom of the boiler and the cabinet.

Although the boiler cupboard does not require any form of air vents or additional ventilation, the boiler requires oxygen in order to burn the gas correctly. The air that’s in the cupboard is sufficient for the boiler to do this, so long as these clearance measurements are in place. This also means that the cupboard should not be airtight. A lack of oxygen could result in the production of carbon monoxide, which could be dangerous.

The boiler should be easily accessible for any servicing or maintenance requirements. This means the door to the cabinet should be openable, and there should be a minimum gap of 700 mm between the boiler and a wall or other obstruction for the engineer to service it properly.

It’s more important that the flue is situated in the right position with correct ventilation. The flue is the pipe that allows the waste gases produced by your boiler to be released from your home.

A horizontal flue system should be at least 300 mm below an openable window, air vent or other ventilation opening. A vertical flue system should be situated at least 1,000 mm from an adjacent opening window. This regulation is in place to prevent any waste gases from re-entering your home.

The boiler should be installed in such a way that the flue terminal is exposed to external air. It is important that this terminal doesn’t become blocked or obstructed and it must allow free passage of air at all times. 

Does a back boiler need ventilation?

A back boiler, just like a regular condensing boiler, doesn’t require any specific air vents or other form of ventilation.

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What is a back boiler?

Back boilers were particularly popular in the 60s and 70s. They were installed behind a fireplace or stove as a way to utilise the heat produced and turn it into hot water for the taps or radiators. They wouldn’t have been the sole source of heat, but rather an additional way to heat water.

Back boilers contain a heat exchanger that’s filled with cold water from the mains. There’s an output at the top of the boiler that allows the warmed water to be transported for use in the home. However, back boilers are around 78 per cent efficient, compared to the 98 per cent efficiency of modern gas-condensing boilers.

They’re rarely in use nowadays, particularly as they were renowned for exploding. When water is heated, it expands. All modern boilers have a way of storing this excess water, whether it’s in an expansion vessel or an additional water tank in the loft. Many back boilers don’t have this. The pressure in the tank can increase until it eventually explodes. The Health and Safety Executive website explains what to do with your redundant back boiler.

Back boilers do not require additional ventilation because any gases will be released via the chimney.

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