ACS help compartment vetilation

[darkart]

Hi all, I have my ACS exams in a few weeks and having a mental block in a home study course, concerning compartment ventilation.

If an open flued 10kw net boiler has compartment ventilation direct to outside, it requires high and low ventilation as follows:

High ventilation is = 5 x 10 = 50cm2
Low ventilation = 10 x 20 = 100cm2

Why is it, if a gas fire (open flue) is fitted within a room you deduct the -7kw for advantageous ventilation.
so: 10 - 7 = 3kw x 5 = 15cm2 ventilation required.

My confusion is, if you -7 Kw for a fire, why is -7kw not deducted from external compartment ventilation for an open flued boiler?

I'm assuming the top external ventilation is for cooling and the bottom ventilation is for combustions so should be worked out same as a gas fire as follows:

Low ventilation: 10kw -7kw = 3 x 5 = 15cm2?

It might seem a stupid question to ask but I'm trying to learn a lot in a short space of time and having a mental block and stopping further progress.

Thanks in advance

 

[picasso]

Rooms have natural ventilation (this is where your 7kw comes from) compartments dont.

 

[OwainDIYer]

You can't always deduct adventitious ventilation - in a modern double-glazed well-sealed house you probably can't.

 

[gas112]

Wrong

 

[FiremanT]

112: Are you referring to Owains answer, or the confusion over "ventilation"?

 

[gas112]

owains answer

 

[AGAS]

You can't always deduct adventitious ventilation - in a modern double-glazed well-sealed house you probably can't.

what do you mean you can't always deduct advantageous air ? double glazing is taken into consideration

 

[Steelmasons]

I think darkart has fooked up on his low level ventilation..

 

[McCombi]

A typo by the looks of it. The end result is correct.. Or is it. I'll report back after this White Russian

 

[Steelmasons]

End result is correct..

 

[McCombi]

Was just jesting, although my memory seems to be deteriorating, keep forgetting things the missus tells me etc, thankfully I still remember the basics of gas safety.