G3 Discharge - to soil stack

[adh]

Hi All,

As part of a new build, we're having a Mechanical Ventilation & Heat Recovery System. This makes it important to ensure an airtight seal on the building, as far as possible. We have the requirement for a discharge from the unvented DHW cylinder in the loft. This made me think about the problem with this discharge being open to atmosphere and the MVHR system we have installed. After some research I came across a product from Hepworth which seems to allow discharge from unvented cylinders into the soil stack. The product is their HEPVo Hygienic Self Sealing Waste Valve. A link to the certification is here:
http://www.redbooklive.com/pdf/042-97.pdf

I've also checked with Hepworth direct and they say it's suitable for discharge from unvented cylinders but can't be used for boiler discharge.

This seems ideal for our scenario but wonder if anyone has any reservations or sees any problems.

 

[Rodreguez]

from when i done my unvented i seem to remember these are ok as long as they are fitted vertically i can av a look at the documentation later just to clarify

 

[adh]

Yes from the schematic I was sent by Hepworth they must be vertical. I've also had a look at the G3 discharge regulations and they seem to allow discharge into the soil stack provided the pipework is either in copper or specified to withstand temperatures which would be expected from a discharge of this type. I assume this means the pipework would have to withstand 100 degree temperatures.

our system incorporates a heat pump rather than traditional boiler. However my one concern is that we are off mains drainage which means we have a self contained treatment plant. I'm not sure whether discharge into this type of plant is allowed. I understand it can interfere with the normal treatment process due to chemicals that may discharge. This would affect the central heating side (UFH) as this has an inhibitor.

 

[Gray0689]

Your discharge pipe from cylinder is from your domestic water not from heating side

 

[adh]

Your discharge pipe from cylinder is from your domestic water not from heating side

Yes but we have two other expansion vessels which also need discharge points. One for the brine circuit on the heat pump and one for the underfloor heating. The UFH circuit will have inhibitor added and would therefore discharge this during a fault. I don't think this is allowed when you have a treatment plant.

 

[Plucky]

The 2 on the heating circuit will not have a tundish so will not be vented to atmospehere

 

[adh]

The 2 on the heating circuit will not have a tundish so will not be vented to atmospehere

The heat pump supplier, Danfoss, have asked for a tundish to discharge from their expansion vessel on the ground loop. They said this must discharge to atmosphere.

 

[oldplumber]

discharge pipe work does not have to go to the treatment plant it can also discharge into a soakaway, its own soakway built for it etc etc

 

[justlead1]

Hi. I read with interest. But have been under the impression that tundish fitted, were in order to identify a discharge from either pressure relief and or temperature relief, at a point close to the appliance, also providing frost protection of appliance, should the discharge pipe freeze downstream of the tundish. Coupled to the fact that the potential of super heated steam discharging into a plastic soil system is far from good, waste water could also be a issue if the warning element of the installation is discharge into a blind situation. On the positive side hot water discharging into the soil and waste system would have no effect on bacteria. I feel it doubtful if the discharge from sealed system would be in sufficient quantity to cause problem with the process. My own experiance suggests, although most problem can be engineerd out as we develop. With out planned maintenance they fail and bite you in the bum. After all a few metres of pipe and ingress through 500 mm SQ. less the frictional resistance is hardly a major issue. Good Luck with the project it sound interesting.