Installing boiler.

[--s-p-o-n-i-x--]

Have decided a combi is the way to go and am going to install it in an existing 'larder' cupboard in the kitchen.

Unfortunately, the plastic soil stack for the house runs down the back of the cupboard.

As the walls of the cupboard are brick, I'm thinking maybe I'll make a false back to the cupboard out of thick plywood, attached to the side walls using battens. I'd then mount the boiler directly to the plywood. The flue can go through the plywood to one side of the soil stack and exit through the brickwork in the normal way.

Is there any reason not to do this?

sponix

[Rick]

I would be very carefull in making sure you can mount the boiler on a combustable surface, I think you can't do this.

Rick

[--s-p-o-n-i-x--]

That's the sort of thing that worries me. Does anyone know for sure?

What constitutes a combustible surface? Does it mean you can't mount it on a wallpapered wall?

sponix

[Andy Hall]

You could use a wallpapered wall but plywood would not be a non-combustible surface.

However, you do need the strength, so you couldn't just use plasterboard on its own either without a suitable frame behind. A typical boiler weighs in the region of 30-40kg.

I would make a timber frame and if the width is much wider than 600mm, put in additional framing timbers, obviously avoiding the flue position. Fit additional horizontal timbers such that the fixing holes for the boiler (some kind of bracket is typical) end up going into timber.

You could take advantage of the void behind the panel to run pipes and cables. However, if this is done, it might be a good idea to make the panel in two sections. The one taking the boiler would be fixed permanently, and then one removable one below or possibly the side depending on the pipe routing.

You can use a fireproof board like Masterboard or Knauf to make the non combustible surface.

[--s-p-o-n-i-x--]

Does it *have* to be non combustible? I have seem conflicting info on this?

If it does have to be non combustible, why is it OK to have wallpaper (which is in itself combustible) behind?

sponix

[Derek ^]

Wallpaper pasted onto a plaster surface won't support combustion on account of it being intimately attached to the much greater mass of the plaster wall (which is intrinsically non-combustible) which keeps it's temperature more or less at the ambient temp. of the interior of the boiler cupboard.

There will be a standard test for this.

DG

[Andy Hall]

AIUI, the issue is the extent to which the material supports and transmits flame.

As far as whether you *have* to use a non-combustible surface is concerned, I always have done because it's an added degree of safety which costs very little. In fact, I have always lined enclosures for boilers with fireproof board on all surfaces.

There is a reference to all of this in part J of the Building Regulations (section on gas burning appliances.)

They do also say that one can follow the boiler manufacturer's instructions. You may find that with some, the manufacturer says that it isn't necessary to take precautions about non-flammability because the case temperature is low. The same issues relate to compartment ventilation.

Either way, I do think that it's important to have a very substantial fixing, and I wouldn't trust 18mm ply to do that on its own - i.e. I think that studs behind are important. Given that situation, there doesn't seem to be any value in using ply vs. using plasterboard.

[John Rumm]

I assume tyou mean the soil pipe runs inside the cupboard stopping you finding enough blank back wall to hang the boler (i.e. not on the outside wall adjacent to the cupboard)

Perhaps my mental picture is wrong, but given that most boilers these days have the flue emerge out of the top of the case at a rotatable turret. Could you not mount the boiler on the side wall of the cupboard and then take the flue sideways out of the back wall to the side of the soil stack.

Failing that get a pipe standaoff for the boiler and pack the mounting plates out far enough such that it stands over the soil pipe.