I have an old Baxi Bermuda back boiler in my dining room which vents into the chimney. The last time it was serviced I was told that I ought to have an air vent in the door leading to my lobby. How large should this be and does it matter whether it is at the top or the bottom of the door?
Thanks....Ron
P.S. I plan to replace this boiler but, until then, I would like it to be safe/legal.
The service report may have said "not up to current standards". My Grandfather got this every year off BG for the last few years, so I core drilled 2 holes through some very hard bricks and put grills on just as the engineer asked for. The bloody boiler packed in 3 weeks later and he now has a balanced flue.
you could trawl through BS 5440-2 which is linked below.
You will need to look at the rating plate of the boiler which is probably hidden behind the fire.
Let's say the boiler has a typical heat input of 60 kBTU/hr
So convert to kW by dividing by 3.412 that's 17.58kW The fire adds another say 5.8kW.
Now the first 7kW is provided for by 'adventitious' air.
So now you have 17.58 + 5.8 -7.0 = 16.38kW
Assuming the door to the lobby is to outside air?
Then you need 4.5 cm^2 / kW of appliance = 73.7 cm^2
If this air is from another internal space then add another 50% for the vent on the lobby door and of course you'll need a vent of 73.7 cm^2 to the outside.
The outside vent should be >150mm above ground level to prevent blockages by leaves/snow.
The vent on the internal door should be < 450mm above the floor to prevent smoke transfer in the case of a fire.
I wonder just how reliable these are? I've got a CO meter for the car - to check and set the CO output on a pre-cat model and it's pretty useless despite costing about 100 quid. The MOT exhaust gas testers are considerably more expensive than this and are checked and calibrated regularly, IIRC.
Good point. I would hope that all CO detectors would have to be tested and approved, but maybe there is nothing forcing manufacturers to do this? However in a domestic boiler setting I would imagine that any CO would be too much so an accurate quantitative measure would be unnecessary.
you need to take the input of the boiler in kw and deduct 7kw for advantitious air then multiply the remainder by 5cm2 and that will give you the amount of free air needed for that appliance, there are other things to take into account aswell but the corgi guy or baxi should have advised you what you need and also the location and even the cost if he wanted the work. if the appliance is/was unsafe it should have been dealt with straight away.
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