Where does a gas CH boiler get its oxygen from?

[epsilonGreedy]

I had previously assumed that when a modern gas central boiler is installed on an outside wall with a thru wall flu the oxygen for the burn would be drawn from air outside the house. However when I started looking into requirements for hiding a boiler inside a cabinet I encountered this explanation and I am now confused.

 

https://www.viessmann.co.uk/heating-advice/does-a-boiler-cupboard-need-ventilation

 

What are the regulations of having a boiler cupboard?

 

Quote

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.

 

[ProDave]

Sounds like a catch all to cover conventional flue boilers?

 

Or is it to allow convection for cooling?

[PeterW]

It’s nothing to do with air flow, it is to do with not creating a negative pressure situation around a casing that could pull fumes through a faulty seal.
 

All boilers need airflow around the casing to both allow the heating and cooling of the casing, vent any minor gas leaks and also to stop any possibility of a negative pressure being created around the boiler. 

[epsilonGreedy]

1 minute ago, PeterW said:

It’s nothing to do with air flow, it is to do with not creating a negative pressure situation around a casing that could pull fumes through a faulty seal.
 

All boilers need airflow around the casing to both allow the heating and cooling of the casing, vent any minor gas leaks and also to stop any possibility of a negative pressure being created around the boiler. 

 

 

My reading of your post is that the air supply to provide oxygen to the boiler is indeed drawn from outside of the house?

[PeterW]

11 minutes ago, epsilonGreedy said:

 

My reading of your post is that the air supply to provide oxygen to the boiler is indeed drawn from outside of the house?

yes it it’s - balanced flue. Most - if not all - New gas boilers in the UK are sold and fitted with a C1x type balanced flue that takes the air from outside. Old B-type flues haven’t been used for years on boilers, and are really confined to gas fires rather than boilers. 
 

That Veissmann link is very badly worded and close to being factually incorrect in a couple of places. 

[epsilonGreedy]

2 hours ago, PeterW said:

That Veissmann link is very badly worded and close to being factually incorrect in a couple of places. 

 

 

I am pleased to read this, thought I had completely misunderstood air flow to boilers.

 

I stumbled into this quandry today after realizing I had designed a kitchen without allowing for a boiler, then thought I had discovered a great way to disguise the boiler in the fake chimney breast that forms the cooker hob alcove.

 

My concept was to fit the boiler into the upper 1/3 of the hollow fake chimney breast however the height maths does not work out after allowing for the working air space around the boiler stated in the Veissmann advice. Floor to hob ceiling height is 1.7m. Then the concealed boiler cabinet would need 720mm for the boiler plus 300mm airspace above and 100mm below = kitchen ceiling height of 2.82m whereas I have 2.4.

 

Time to investigate floor level under counter top boiler installation because we are typing to keep the walls as un cluttered as possible.

[PeterW]

10 hours ago, epsilonGreedy said:

Time to investigate floor level under counter top boiler installation because we are typing to keep the walls as un cluttered as possible.

Put it in the garage if it’s close by..? Or attic space is preferable as long as it’s accessible