ventilation

[bster]

just had a gas safety on a baxi BBU and there was a slight prob with the vent size (needs 90mm2 only got 60ish), this got me thinking


If a BBU has an input of 20kw (boiler) and 5kw(fire front) then you add them together = 25 - 7kw allowance means that the vent is calculated on 19kw.

but if you had a seperate 20kw boiler and 5kw fire in the same room you would take the 20kw boiler only and after 7kw allowance the ventilation calculation will be based on 13kw and not 19kw.

why is this? (or have i read it wrong in the Viper book).

 

[EliteHeat]

Ventilation for all open flued appliances is based on the sum of the heat input for all appliances within the room. Deduct adventitious allowance only if located within habitable space.

It is different in the case of 'through' rooms I believe, such as a lounge/diner where they are really two seperate rooms that have been knocked through.

 

[bster]

in the Viper book it shows 3 appliances though 2 of them were flueless so is this why (in the example from book) that they were taking the highest rated appliance (which happened to be an open flued combi) only then deducting 7kw and not adding them all together. and deducting 7?

 

[Gasguru]

Yes refer to the BS table and MI's for flueless ventillation requirements.

 

[bster]

got it now!

you take the greater of the three groups stated. (total flueless or total open flued etc..).

cheers