Johnson and Starley warm air - ventilation

[DaveM543]

Can someone clarify the ventilation requirements fo a JS J70/90 Mk2
The boiler is in a compartment with a door. The door I believe has adequate ventilation of the high level grill 55 sq ins and low level grills 94 sq ins. The book in words says that the external wall ventilation shoud be at least 21 sq ins, but the table refers to the external wall ventilation being 24sq ins AND a low level of 47 sq ins. Is this correct as I am somewhat shocked at the free area hole required in the wall, What is the thermal loss from a 72 sq ins hole?
We currently have the high level outside wall vent, but no low level vent

 

[geoffgiltrap1]

Perhaps it only applies if an extractor fan is fitted in same room. Its a long time since I last did warm air and then we only fitted one combustion air grill direct to outside if w/a unit is in same room. Double check your instructions.

 

[gas112]

High and low vents to outside is when it is vented to outside from within the cupboard if you have proper compartment ventilation in the door then only one vent to outside is required directly from that room .
So you need the 21 square in vent

 

[DaveM543]

Thanks , that is very useful and reassuring.

 

[Agile]

Its also quite important to get older WAUs serviced regularly as the inner heat exchanger can rust and the holes can allow products of combustion to enter the room.

Cleaning/replacing the filter can be done by the user and depends on how much dust/fur is produced in the house. I suggest every three months typically.

Tony