Cavity Wall Insulation & Ventilation

I have just had a survey to assess part of my house for cavity wall insulation. My house is in two parts; the original house and a large extension. The original part has been insulated by the previous owners. I was seeking to fill the cavity in the newer part which isn't insulated. The man walked around the new part and noted the ventilator on the outside which was part of the build ince there is a "flame-effect" fire in there. "Not big enough", he said, "It must be enlarged to about a square foot cross-section". He went on around the house and noted that we have an open fire in the older, already insulated, part. "We'll have to put a ventilator into this room, too" he said, "there should be one in that room too" I suggested that I hadn't asked him to look at the rest of the house which was insulated and he said it was the law. I suggested that he should partake in some "Sex & Travel".
So the questions are: 1. What are the rules about ventilation when a cavity is filled? 2. If the filling reduces air flow to such fires, how does air percolate today? Through the plastered walls or up thru' the concrete floor? 3. What are the rules about retro-fitting old parts of a house to newer standards? E.G If I had new wiring in part of my house it would be Brown/Blue. By the same logic as the cavity wall person applied, the electrician might insist on ripping all the older red/black wire in the older parts not being upgraded..patently daft.
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An ignorant sales droid trying it on! Ventilation through any cavity should be by a sleeved unit so whether the cavity is filled or not makes no difference. For the actual free area of any ventilator required for a gas appliance take a look at the installation and maintenance instructions or ask the manufacturer. However there is always a caveat that all products of combustion should go up the flue without spillage into the room.
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In article

Good for you. To be fair though, I think these guys (who must be coining it) are frightened of being checked by The Man, i.e. government inspectors who come round at random, since the government (i.e. WE!) are subsiding this exercise -- so: Fair Play.
We had cavity wall insulation put in last year, and the loft topped up. The guys were fine (amazingly efficient and quick (I was watching them, on and off!)), but they weren't what you'd call professional workmen: just a bunch of lads who'd got a job with the firm, riding this wave of demand.
My point is: they were quite worried about the loft part: they couldn't fill the loft, because part of it is floored. At first they said: we can't do this loft because we can't do the whole thing. I pointed out that their "surveyor" had checked and OK'd it previously, so we agreed that if they left enough insulation up there to do the whole loft, I would say that it was me who had rolled it back, to make the boarding available for storage.
They also fitted hooks and eyes to the loft hatch: these were completely unnecessary (and I took them off later). It was clear that they were dotting i's and crossing t's for the benefit of the random inspector (who's never turned up yet).
John
p.s. The whole job was very worthwhile: the house has been noticeably warmer.
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What about the suggested retro-fit to another part of the house, insulated more than 15 years ago? Naffer
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I believe each sleeved vent costs 75 or more to fit.
Thus it's a bit like kitchen fitters - commission on the number of cupboards, with one 1820 house having 48 cupboards. It's impressive, you get a workout trying to work out which cupboard has anything in.
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