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