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Central Heating

Part H building regulations

Anonymous user 17/02/2026 - 7.58 AM

I have been told that the new regulations require a 40mm hi heat waste condensation pipe needed for the bolier venting outlet into the waste, however my new WBosh combi boiler is in the loft and I would to vent out of the gable end into the soil stack pipe, do I to use 40mm hot water pipe as it will be insulated?

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2 Answers

Southside Heating and Plumbing

Rating: 5 out of 5

Edinburgh

If the condensate pipe is outside it needs to be at least 30mm, insulated and no longer than 3m. That said, if there’s a way to connect to the solid stack internally that will always be the preferred option.

Answered13 February 2026

YK Heating Services

Rating: 5 out of 5

Cambridge

For external condense pipes we use minimum 32mm pipes, if it’s internal then 21.5mm one will do the job.

Answered17 February 2026