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Reduce DHW Temperature

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  rev. 2008-11-25        

Existing Conditions

Domestic Hot Water is currently being supplied to the building at xxx°C (xxx°F).  Although many people like it this hot, it is much hotter than necessary.  In fact, many jurisdictions legally require DHW to be much cooler, to minimize the risk of accidental scalding.

Retrofit Conditions

The aquastatic control should be set for 49°C (120°F), which is the maximum allowed in many jurisdictions.

Further Benefits



Application Details

This is a simple adjustment on the heater aquastat, or a setting in a building automation system or electronic unitary controller.

Issues and Concerns

There has been some debate in the heating and plumbing industries about the low a setting for DHW temperature.  For one thing, many residential tenant are accustomed to DHW temperature of 130°F or warmer.  However there is no doubt that a lower temperature is adequate for normal domestic needs and is both safer and more energy efficient.

The more important concern is with claims that low DHW temperature in storage tanks provides a growth environment for legionella bacteria.  Legionella can be deadly to those with weak or impaired respiratory systems.

At this point there is no good scientific evidence that DHW in the temperature ranges we're dealing with has created a problem.  The issue is well know, and medical organizations in a position to weigh the risks come down clearly in favour of lower temperatures for scald prevention.


Conforms to recommendations in "Energy and Water Efficiency in Multi-Unit Residential Buildings", Canada Mortgage and Housing Corp.



Gallons/day x 8.33 x DeltaT ºF x 365 x $/Btu = $/year saved


* $/Btu Ngas = $0.000011327/Btu

* DeltaT ºF = Existing hot water supply temp - New hot water supply temp



1000 x 8.33 x 10 x 365 x 0.000011327 = $344.39/year saved

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