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Discuss Need for Mixing Valve out outlet from the DHW tank in the Plumbing Forum area at UKPlumbersForums.co.uk.

  1. surfcob

    surfcob New Member

    Hi all,
    the heating system in a bungalow that uses an Air to Water heat pump has a TMV (thermostatic mixing valve) at the outlet from the DHW tank. It is a gravity system. While the shower is pumped and there is no bath, the TMV is likely to impact on the flow to the WHB and Kitchen sink.

    Can the TMV at the outlet from the DHW tank be left out?

    Looking at Irish Building regulations, there does seem to be a requirement to fit a TMV. In UK Regs Sanitation, hot water safety and water efficiency Part G, a bath needs a TMV and CIBSE reference the need for TMVs in NHS/care type buildings,

    Perhaps TMVs are not needed in Irish Houses?
  2. chris watkins

    chris watkins Plumber

    I don't know Irish Building Regs (maybe Best could help) but the normal reason for installing a TMV on the cylinder outlet (known as a tempering valve) is if there is a danger of overheating domestic water from an uncontrolled heat source such a solid fuel boilers or solar systems & they are normally set to give a max temp of 65 - 70 Deg C. Any storage of hot water held in a vessel would be expected to be at a minimum of 55 Deg C.

    The Part G & DO8 you quote is a requirement for point of use temperature control to avoid the danger of scalding. (one must be installed to a newly installed bath in the UK.

    To my knowledge domestic hot water from heat pumps is limited in the maximum temperature that can produce but I stand to be corrected.
    Ask the manufacturers ?
    • Like Like x 1
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