Unvented discharge pipework

[SmokeyJ]

Hi all, sorry for the long post.
Looking for some advice. Went out to a ground floor flat to look at fitting an unvented cylinder.
Problem is the airing cuoboard is in the middle of the flat with no real way to get the discharge to outside. He has had another quote which allows to run it into the soil stack in the bathroom. Wasn't aware you could tbh and only re-sat my unvented a month ago with no mention of discharge into soil stack, not even in training books they provided.
Reading up I see that it can be ran into a soil stack via a hepvo trap and using polypropelyne pipework, providing it can be demonstrated that the soil stack can whitstand discharge temperature. Soil is boxed in atm so no idea what it is, I'm assuming plastic as flat not old enough to be metal
Without knowing the make of soil pipe how can you confirm its acceptable?
Can standard soil pipe handle the high temperature?
Seems like a bit of a grey area and wanted so see what others opinions are on it?
Thanks Jason

 

[Last Plumber]

That's in Doc G3 section 3.6.

Have you a copy to read? or do you know what it says?

 

[Last Plumber]

There is a Link Here if you need to read it
Page 25 Para 3:6

 

[ShaunCorbs]

Yes I would be happy putting the discharge into the stack

 

[SmokeyJ]

I've read g3 which 3.57 says metals or other materials can be used if it can withstand temperature.
3.60 Then says not to connect to a stack unless it can be demonstrated it can withstand the temperature.
It then gives you appropriate materials for D2 branch pipework PB or PEX but doesn't refer to the stack material.
The nhbc 8.1/26 guidance refers to polypropylene.
A British Federation Of Plastics note refers to the stack material as being PVC-U and PE.
Gets a little confusing

 

[SmokeyJ]

Nhbc and bfp notes show the same diagram but only bfp one refers to the stack material.

 

[ShaunCorbs]

Your in an apartment so the chances are something else is going to be running to cool the water

These days communal stacks are fusion welded (hdpe) which can take the temp no problem

 

[SmokeyJ]

Good point. Think I might be being too over cautious.
Regarding the connection to the stack it looks like a boss section is preferred over a strap on boss.

 

[ShaunCorbs]

I would think a strap on boss is fine or the mechanical type

 

[townfanjon]

My take on it .... in an existing flat, you have no idea if the soil pipe would take the discharge .
A place I look after is full of thermal stores , but over the years a local firm of bodgers has put 3 maybe 4 unventeds in it . I always replace the cylinders with thermal stores , and will wet myself if one of the unventeds shags a soil pipe .
Be careful with your decision

 

[andyplumber]

You can connect in to soil stack as per Regs but some manufactures won't allow you to connect to soil, I went to priced a customer supplied Gledhill unvented a year ago but as the cylinder was in a airing cupboard below ground i had no way of getting the discharge out but there was a soil stack in the corner of the cupboard and the Gledhill installation guide didn't show the soil stack connection I rang them and they wouldn't allow it to be done so I changed the cylinder to a RM Stelflow cheaper than a megaflo.

 

[stratplus]

You can connect in to soil stack as per Regs but some manufactures won't allow you to connect to soil, I went to priced a customer supplied Gledhill unvented a year ago but as the cylinder was in a airing cupboard below ground i had no way of getting the discharge out but there was a soil stack in the corner of the cupboard and the Gledhill installation guide didn't show the soil stack connection I rang them and they wouldn't allow it to be done so I changed the cylinder to a RM Stelflow cheaper than a megaflo.

Connected unvented cylinders into plastic soil stacks for years. Standard practice for companies I’ve worked for. Always used tundish/hepvo and pushfit Pipe with pushfit fittings. Polypipe stacks. Done on many many sites, never heard of any issues.
Understand the concerns about the plastic solvent stack so raised the question with someone “in the know” manufacturer wise. Gave me a couple of scenarios such as:
How often do you empty a pan of boiling hot water from cooking into your kitchen sink straight off the stove?
The pipework under your kitchen is often solvent weld. Have you ever known it to melt or have the solvent weld fail?

 

[stratplus]

Connected unvented cylinders into plastic soil stacks for years. Standard practice for companies I’ve worked for. Always used tundish/hepvo and pushfit Pipe with pushfit fittings. Polypipe stacks. Done on many many sites, never heard of any issues.
Understand the concerns about the plastic solvent stack so raised the question with someone “in the know” manufacturer wise. Gave me a couple of scenarios such as:
How often do you empty a pan of boiling hot water from cooking into your kitchen sink straight off the stoke?
The pipework under your kitchen is often solvent weld. Have you ever known it to melt or have the solvent weld fail?

Although my question was for running a boiler PRV into the stack not unvented which could flash steam.

 

[Last Plumber]

It’s all crackers if you ask me.

How many people tip the boiling spud water in the sink?

It all goes in same place at the same temp.

If fact, truth be known, the spud water is more than likely hotter and it’s done on a regular basis amongst other things people chuck in the sink.
Boiling liquids, hot fats etc.

I know it’s not good practice but you try telling every household in the country not to put hot things down the plastic waste.
You’re on a hiding to nothing with that one.

How many melted sink wastes have you replaced due to Mrs Groggins spud water?


My opinions
Mini rant over!

 

[Last Plumber]

I’ve just re read the thread and realised I made similar comments to stratplus.

That must make it ‘common sense’ then ?

 

[ShaunCorbs]

How many commercial sites have sterilisers that discharge into stacks

 

[SmokeyJ]

Good point and tbh I've seen countless 15/30L unvented water heaters with the discharge going into say the kitchen sink waste.
Thanks for the input lads, I think I'll go into the stack as really would rather fit an unvented than say a Pulsacoil or similar.