Ventilation of old E Type Boiler Query

25 Feb 2017
Reaction score
United Kingdom
Hi All

I bought my current property 2 years ago where the water and central heating are powered by an ideal e type boiler CF 105N that works fine. It is housed in its own room, 9 foot by 5 foot by 7 foot with a door opening onto a corridor which has top and bottom vents.

The boiler itself has a vertical flue and exits via a lined flue up a chimney.Ventillation for the boiler is provided by two four inch pipes which vent to the outside of the building. The lower of the pipes has an extractor fitted that is controlled by the boiler. The extractor generates a constant exchange of air from outside when the boiler is operating.

There is also a carbon monoxide detector sited just inside the door of the room at eye level.

I have recently found a gas report from 4 years ago stating that the ventillation for the boiler was inadequate, but I believe that that report must have been issued before the ventilation was installed, otherwise why would someone go to the expense of installing new vents and extractor that were not compliant?.The new ventillation pipes and extractor look relatively new.

My thoughts on the ventillation are as follows. The boiler manual says the external ventillation must be 155cm2 for this model (manual dated 1977).The gross gas input for this model at full blast is 41.3kW, which nets down to 37.5kW. After subtracting 7kW and multiplying by 5 gives a ventillation requirement of 152.5cm2, slightly less than that stated in the manual.

When the boiler is working there is forced transfer of air via the two vent pipes, the area of which equates to 162cm2 - calculated as follows:- 5.08cm radius*5.08radius*3.142 *2. Even if the extractor stopped working, there will still be two vent pipes, directly connected to outside with a combined area of 162cm2.I obviously want to get the boiler serviced, as I have no idea how long ago it was done, but it concerns me that I have to pick an engineer, at random, who may find it more commercially attractive to state that my boiler has insufficient ventillation and instead of a service propose a nice new expensive boiler on an outside wall with all the associated re-piping costs on top. This I simply cannot afford.
I would appreciate any thoughts on the above.Many thanks
Sponsored Links
So low level ventilation is being extracted? exactly is the boiler interlocked via the extract fan?
I'm trying not to spit my beer all over the fookin keyboard...:ROFLMAO::ROFLMAO::ROFLMAO:
Hi - thanks for your response. There are 2 4 inch pipes, one sucks out air from near the ceiling of the room due to the negative pressure caused by the extractor pulling air from outside towards the bottom of the room. Extractor is connected to boiler via a heat thermostat i believe.
So the extracter fan is now pulling air into boiler room from outside???..come back when you've made your mind up.
Sponsored Links
BTW , leave the ventilation calculations to someone who actually knows what they are doing.
Sorry I meant positive pressure! - air flows to the outside from top pipe due to positive pressure generated by extractor pulling in air from outside in bottom pipe.
So a "heat thermostat" interlock has been installed for a "no air" situation?
I suggest you call a professional.
BTW , what would be the 'free area' of that 4" air intake taking into account the fan being stuck on the end of it??
If the extractor was removed and there only existed the 2, 4inch vent pipes there would be 162cm2 of venting to the outside which exceeds that stated in the boiler manual let alone my own "chimpy" calculations!
Even if the extractor stopped working, there will still be two vent pipes, directly connected to outside with a combined area of 162cm 2
Should the "extractor fan stop working" the boiler would also "stop working" due to the safety interlock.
Fair point - that would be the case - however removing the extractor would leave 162cm2 of free air, not requiring any extraction or interlock
Low level ventilation = 375 cm2
High level ventilation = 187.5 cm2.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links