Installing new boiler in cupboard on outside wall

[adamr]

I'm about to have an ancient Potterton floor-standing boiler replaced with a new, condensing wall-mounted model (Vaillant Ecomax).

In order to save space in the room it's currently installed in, I had the idea of having the new boiler mounted on the other side of the wall, ie on the outside of the house, and enclosed by an exterior cupboard, shed-like structure - something like this, with the interior clad in a fireproof board like Supalux.

I've found a Corgi-registered plumber who's happy to do the installation, but wants me to take care of the construction of the shed, which I'm happy to do.

Has anyone here done an installation like this, and have you any advice for me, particularly regarding the weatherproofing and fireproofing of the cupboard?

Many thanks in advance

Adam

 

[doitall]

No problem from doitall

However, being as modern boilers are about as reliable as a Virgin train You should consider alternative frost protection from an electric heater, in addition to a frost stat on the boiler and high insulation values to the enclosure (shed)

 

[Agile]

As John says no problem.

Providing the boiler is not too close to any part of the combustible shed there is no need to use a fireproof lining.

Better to concentrate on lining with waterproof material and insulation and making sure its fully weatherproof. Many I see have leaky doors and totally open bottoms.

Tony

 

[adamr]

Thanks for the advice guys.

Agile, do you have any tips on how best to achieve the weatherproofing? I'd been planning to caulk all the internal joins with silicone, and had hoped that the layer of Supalux would do the trick - but on checking again I notice the manufacturer doesn't mention it's waterproof, so it probably isn't. I see they do another product, Masterboard, which is 'resistant to the effects of moisture', so possibly this would be a better bet. You mention insulation - would you recommend I put a layer of rockwool between the outer skin of the shed and the lining board, rather than just screwing the board straight onto the shed wall?

Doitall, are you really saying that the frost stat built into the Vaillant Ecomax is so unreliable that I need to install a separate heater? If you really, really think I need to do this, what kind of heater did you have in mind - something like this connected to the mains through a normal frost stat?

Many thanks for your help...

Adam

 

[Agile]

In my view you would be better off insulating the shed wall and sealing the joints with silicone. You dont really need a waterproof material if you use something like plywood or plasterboard. It does NOT need any ventilation with this boiler but you must have about 150 mm minimum all around the boiler to allow air to circulate.

Lag all internal pipes and make VERY sure the door is totally sealed to wind and driven water.

Think first about the flue!

Tony

 

[htgeng]

IMO, I would build or have a joiner build a bespoke double skinned cupboard. Those shed-sheds are very flimsy.

 

[doitall]

You need to get as much rockwool or other insulation as possible, the inside could then be boarded with 25mm shuttering ply or even plasterboard, you could ply and finish with plasterboard whatever it needs a good surface for fixing and to be atmospheric dry or the electric bits will suffer.

Water proofing will depend on roof covering, Felt, tiles or sheets, a lead flashing can seal the wall provided the pitch is above 32%.

Doitall, are you really saying that the frost stat built into the Vaillant Ecomax is so unreliable

No I'm saying I would not rely on the boiler to keep the house protected if I was away for more than a day

 

[gazthepottertonengineer]

sounds better than the boiler i went out to the other day which was literally on an outside wall with tarporline over it and he wondered why it wasnt working and said that it was going to be bricked in next month quality

 

[brumylad]

Why not build the walls of the structure from single skin brick or block work. If the masonary structure of the walls is continued over the door, on a lintel , and up for say eighteen inches , then you could perhaps bring the flue out through the side wall or the front of the structure instead of having the trouble of trying to take it out through the felt roof of a wooden structure.

 

[doitall]

sounds better than the boiler i went out to the other day which was literally on an outside wall with tarporline over it and he wondered why it wasnt working and said that it was going to be bricked in next month quality

Got a pic for our archives

 

[ChrisR]

I daresay you've seen:
4.1 General
The boiler should be mounted on a flat and vertical area
of wall of sufficient area for the boiler plus the required
clearances for installation and servicing (fig. 3.8). These
are shown on the installation template supplied with the
boiler and are :
- 5 mm either side of the boiler
- 145 mm below the boiler
- 205 mm* above the boiler for ecoMAX 613/2, 618/2,
622/2, 824/2 and 828/2 when utilising the 100 mm
outside diameter flue
- 220 mm* above the boiler for ecoMAX 835/2 boiler,
also for other ecoMAX 600 and 800 series boilers
when utilising the 125 mm outside diameter flue.
- 500 mm in front of the boiler**
** This clearance is only required to enable easier
access to the boiler for servicing and may be
provided by an openable door, etc.
Note:
If the boiler is to be fitted in a timber framed
building, it should be fitted in accordance
with British Gas publication DM2 ÔGuide for
gas installations in timber framed housingÕ.

I don't see a desperate need to insulate the building or a need to "allow air to circulate" as Tony has it. I'd want the building draught free.
Insulating pipes would be obvious.

For £25 that heater with a suitable stat would help sleep at night.

 

[adamr]

Thanks all for the advice.

I think I'm going to construct my own bespoke cupboard from a frame of pressure-treated 2x2, faced externally and internally in 12mm marine ply, with silicone in all the joints. Then bolt the frame to the wall using rawlbolts, with silicone in the holes, and between the brickwork and the frame.

I thought of doing the roof in EPDM bonded to another sheet of marine ply, brought up the wall and chased into the mortar between two courses of bricks, again sealed in with silicone.

On such a small structure, do I need to bother with guttering on the low edge of the roof? Or just construct it with an overhanging lip so the rain will run off the front?

Anyone have any helpful comments/suggestions about this approach? Or know where I might be able to lay my hands on a tiny (about 1 sqm) piece of EPDM?

I haven't managed to find "British Gas publication DM2 'Guide for gas installations in timber framed housing'" on the web - can anyone oblige with a link or post?

Many thanks again

Adam

 

[doitall]

The roof should be weather proofed with a proper flashing e.g. lead.

depending on the boiler the flue should be a min 300mm from the wall so consideration should be given to this now

 

[gazthepottertonengineer]

sounds better than the boiler i went out to the other day which was literally on an outside wall with tarporline over it and he wondered why it wasnt working and said that it was going to be bricked in next month quality

Got a pic for our archives

no sorry i havent

 

[adamr]

OK, so I was thinking the flue would come out the front of the cupboard, through a fixed panel above the door - that way it's kept clear of the wall, and away from the plastic wastepipes which run above where the cupboard will be.

I thought that with a modern roofing material like EPDM it wasn't necessary to also fit a separate lead flashing - is that not right?

I also wanted to ask, do you think it's a good idea to design a backless shed, so the boiler is mounted directly on the brickwork, as is the frame of the shed itself (with layer of silicone inbetween), rather than having a timber rear panel which would require a layer of Supalux between it and the boiler?

Many thanks for your wisdom...

Adam