Vent for gas boiler

My mother recently had her annual central heating service and safety check by Scottish Gas. They have advised that she needs a 100cm2 wall vent ("direct to the outside") in the kitchen where the (conventional flue) boiler is. There is an existing vent in the floor in front of the boiler. I don't know the size of this vent but it's likely to be a bit smaller than 100cm2. The floor is wooden suspended - probably about 18" to 2' off the ground, and there is an external vent in the wall under the floor in the kitchen.
The layout of the kitchen along the outside wall is boiler (freestanding with a fair gap either side), then electric cooker (again freestanding), then washing machine (again freestanding, but under a worktop/side supports, a couple of inches gap either side). The washing machine is also under a window.
According to my mother (who is 86, & often gets things confused), the engineer said the vent should go behind the washing machine under the window, however she didn't know *why* he suggested that (perhaps easiest access for him + drill?). I can't think of any advantage having the vent partially obscured by a washing machine and under a window. Behind the boiler is the obvious place to put it, but it wouldn't be quite so easy to get access from the inside, and the area is tiled (although after 40 years of boiler heat I'm fairly sure the tiles could be persuaded to come off the wall in one piece, and there may be a few spares kicking around.
There's obviously a safety angle to this, I think SG's quote for the work is very reasonable (66), so I'm quite happy to have the work done, but not if there's no need for it.
I have two questions:
(1) Is it necessary to have such a vent in a situation where the vent can be provided via a suspended floor, or does it have to be directly through an outside wall? I'm thinking that enlarging the existing vent might be an option.
(2) If it has to be done, is there any reason why the vent should go behind the washing machine and under the window, when it could be put almost directly behind the boiler, where it would be less likely to cause a draught, and would be supplying air directly to the boiler?
Thanks Biggles
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On Tue, 22 Aug 2006 05:14:49 -0700, b-f-g wrote:

I have a certain sense of deja-vu about this type of thread...
The requirements for ventilation are as set out in BS 5400-2 (links below). You will need to know the input power of the boiler in order to work out the required ventilation. The first 7kW is "free". The floor vent may have to be bigger because it is not directly from outside air.
Behind the washing machine will not cause a draught and may let the installer off some making good.
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Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
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The original vents for the boilers on this estate were on the front kitchen wall behind the washing machine and on the flank kitchen wall top and bottom. Plenty. Except in many cases the front door has been moved to beyond the vents on the flank and you can often see tape over the vents in the front wall. Arguably this doesn't matter for many of the boilers as looking up you can see from the terminal on the roof that they've been changed to a balanced flue.
However, I'm sure most of them are still using gas hobs with no appreciable ventilation in the kitchen at all.
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Skipweasel
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On Tue, 22 Aug 2006 21:14:30 +0100, Guy King wrote:

Also in BS 5440-2 are the rules for FLUELESS appliances like hobs. The rule is that no additional purpose provided ventilation is required provided: a) The room is > 10m^3 b) There is a door, window or other opening direct to outside air.
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Ed Sirett - Property maintainer and registered gas fitter.
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