T&P discharge to uPVC soil pipe

[frank999]

Its advised not to discharge from P&T valve into plastic pipework.
I was hoping a nearby horizontal uPVC soil pipe running under floor boards could be used, but am unsure with this guidance.
I note the recommendation is to go to an external gully below a fixed grating, I've done the resistance calculations and the run is under the 9mt for 22mm ... roughly 7.7mt.

Question is - the gully is also uPVC ... recently installed, assuming there is some temperature drop over the 7.7mt, its still going to be steaming hot, and possibly damaging to the plastic, if doscharging for long periods ... so what is good practice where there is a uPVC gully.

 

[Ian H]

Won’t the gully be full of cold water?

 

[Madrab]

You can use plastic soil pipe for high temp discharge/relief systems but I believe it needs to conform to BS EN 1451-1 (BS5254)

 

[frank999]

Won’t the gully be full of cold water?
Yes at the level of the trap, you could put the level of the pipe down into the cold water, but would there not be risk of siphoning? higher then it would discharge onto the plastic edges of the gully.

I believe it needs to conform to BS EN 1451-1 (BS5254)
Brown underground drainage has been used, which is EN1329-1 (BS4514)

Only difference I can see between brown vs grey/black is UV stability, and the section of brown used is under floor boards, well away from any sun or light, but not sure if it has any more or less ability to sustain hot steaming water for prolonged periods ... they make kettles out of uPVC ! with plastics which seems even less hardy than soil pipe.

 

[Madrab]

The spec BS En 1451 is more based around PP and push fit/compression pipe up to 50mm where a T&P may discharge into after the tundish, but the soil pipe should be rated as high temp, distance dependent.

I'd need to check what the PVC soil standard would be but in the main I don't think PVC-U takes a lot of heat continuously - 70 odd deg - polypipe don't guarantee their PVC-U much above that for anything more than a couple of mins but again it depends on how far away from the heat source it is, that determines how hot the water is by the time it gets there.

 

[Madrab]

Oh and kettles are made on PP or LDPE , not PVC

 

[frank999]

Where does Solvent weld pipe - under BS 1455 sit in all this, the description again states (as it does for BS1453 and BS1451):
'Plastic piping systems for soil and waste DISCHARGE (low and high temperature)'

I note there are solvent weld versions of Soil pipes ... not that I have used those.

I don't think PVC-U takes a lot of heat continuously - 70 odd deg - polypipe don't guarantee their PVC-U much above that for anything more than a couple of mins
Interesting.
Are the various BS standards above that use the common descrpition 'waste DISCHARGE (low and high temperature)' misleading.
An unvented cylinders discharge or drain cock are likely to bring the various types of plastics into contact with steaming hot water at up to 100 degrees.

What is 'high temperature' in context of the Standards.

If deciding to drain down the tank via Solvent weld you could let the water cool off, or push cold water into it before opening the valve.

Kitchen sinks have boiled water emptied down them when people experience blocked drains, water boiled in a plastic kettle.

Are plastic kettles made from 'high performance' plastics ....

 

[frank999]

This document gives prescriptive information:
Approved Document G
Frequently Asked Questions
https://assets.publishing.service.g...chment_data/file/509352/160321_Part_G_FAQ.pdf

Paragraph 3.60 of the Approved Document says that if a discharge pipe is connected to a soil stack the discharge pipe should be either polybutalene or cross linked 8 polyethylene. Does this mean a polypropylene discharge pipe cannot be used?
As stated in its Introduction section, the guidance in the Approved Document is intended to provide advice on how to comply with the requirements set out in the Building Regulations and that “there may well be other ways of achieving compliance with the requirements”. The Department’s view is that it would be acceptable, subject to also complying with sub-paragraphs a, b and d of 3.60, for these pipes to be polypropylene to BS EN 1451-1, as recommended in BRE Information Paper 8/07.

Paragraph 3.60 of the Approved Document allows safety relief discharge pipes to connect to a soil stack if it can safely resist the temperature of the water discharged. Which materials are considered to be suitable?
Metal pipework, such as cast iron, is suitable. For smaller hot water systems, BRE Information Paper 8/07 indicates that discharges can be made to PVCu stacks, provided that: relief discharge is from domestic unvented hot water storage systems only – not combi boilers or sealed system boilers. storage volumes do not exceed about 210 litres. stacks are fully ventilated (ie. no stack cap or air admittance valve). pipework complies with BS EN 1329-1:2000 or BS 4514:2001.

So although I have drainage soil pipes to BS4514, the above states:
not combi boilers or sealed system boilers. storage volumes do not exceed about 210 litres.
I have a 250 litre tank on an unvented system (sealed system) - so quess the answer is no, I can't connect to the PVCu plastic soil pipe under the floor.
So taking the discharge pipe outside, solves part of the problem, but its still discharging to a 'plastic' gully ... if a number of metres away.

A call to Floplast suggests that the run of discharge pipe (in copper) and it being an external gully, it should be ok.
Floplast also commented on discharging to uPVC soil pipes - stating that hot water even at 50-60 degrees - their plastic soil pipes will start to deform, at 200 degrees it will actually melt ... so either way - least you would get would be a drooping Soil pipe on a horizontal run, which obviously this would be a problem.

Still unsure if in the context of undergroung drainage pipes, the 'u' in 'uPVC' (or could be PVC-U) refers to 'underground' or 'unplasticised' ?
EN 1401 suggests it is 'U' for 'underground', yet BS EN 12608 (plastic window profiles) suggests it is 'unplasticised'.

 

[Madrab]

The U in UPCV/PVC-U stand for unplasticised - Poly Vinyl Chloride. It's basically the chemical processing & components of the plastic.

PP is similar to ABS as far as it's heat threshold is concerned. Compression traps are invariably PP.

A perfect example though is where you look at an unclipped run of 40mm ABS waste pipe on a wall, over time it sags, that's primarily down to heat, over time.

It really is a judgment call .... need to consider > how far away is the plastic that's a concern > how hot will the water be when it gets there > how long does it need to cope with that heat (how long would the overheated water be running before someone says, oh better shut that off).

Usually after all that, the risk can be mitigated to low/minimal by design.

 

[frank999]

Just spoke to Kingspan Technical - who's Cylinder we have purchased.

It was advised not to run it to the plastic gully, but run it to ground ... 100mm above, guarded (to avoid small fingers getting near the outlet).
As there is block paving along the side of the property it will be terminated on the outside wall there, with one of these around the end: