Hi All Having a new boiler fitted in my detached garage which is partly converted to a utility room. There is an alleyway inbetween the garage and the house. The boiler is being fitted so the flue is in the alleyway, but plumber is saying I need to get a vertical flue instead as there needs to be 2m distance between the horizontal flue and the wall. The alleyway width is approx 0.9m. Is this correct, as not heard of this before? Thanks.