Here’s a Burning issue: a Building Regulations review is intended to protect us from scalding ourselves. But Geoff Hobbs of Rinnai UK thinks thermostatic mixing valves are not the only solution.
The forthcoming review of Part G of the Building Regulations in England and Wales involves a consultation on the fitting of thermostatic mixing valves (TMVs) in all new domestic premises and bathrooms.

Scalding occurs at temperatures much lower than the boiling point of water; water at 49ºC can cause injury, with babies and small children most at risk.

But before we rush into another regulation-driven spending spree, is it politically correct to look at the broader argument? What about consideration of the carbon footprint that the manufacture and installation of the millions of TMVs required to achieve this safety development implies?

The need to do it in the first instance can only arise, we suppose, from the fact that most of today's hot-water systems do not have any thermostatic output control.
But they do, don't they?

Killing bacteria

Immersion heaters have integral thermostats, and boilers have thermostats too. In order to avoid bacteriological contamination of hot-water tanks, storage temperatures must not fall below 60˚C - well into the scalding range.

So this move towards safety, seems more a matter of balancing more general health issues with the resultant risk of scalding they cause.

Whatever the logic of the proposal, one key fact has been overlooked: if your hot water is supplied by a modern continuous-flow gas water heater, you already have all the necessary safeguards in place.

Moreover, no storage of any hot water is necessary, so there is no need to maintain it at a temperature that would scald. Therefore an additional TMV is not required to control the output temperature at the tap; the heater itself is a virtual TMV.

Continuous-flow gas water heaters electronically control output temperatures within 1˚C, even if a tap is turned on or a toilet is flushed elsewhere in the house, more accurately in fact than TMVs can.

They operate in a similar way to the hot water supplied by a combi-boiler. Most importantly, they are temperature- not flow-rate-controlled, and thus not susceptible to running too hot if cold water is drawn off elsewhere in the premises.

The gas, tankless water-heating concept is simple. Heat the water needed when it is needed, only for as long as it is needed. But when the water is turned off, it goes off. Of course, if all the hot water needed is supplied in this way, this means no cold-water header/expansion tank, no hot-water cylinder, and no associated pipe work.
The resulting hot water is supplied to the point of delivery - the tap - at a safe preset-regulated temperature. The result is that additional protection against scalding is not required.

Furthermore, having already mentioned the carbon impact of this proposal when using all those extra TMVs, the energy used to supply the hot water using the continuous flow method is around 30% less than that consumed by a tanked storage system.

Carbon footprint

The latest thinking on the supply of domestic hot water and heating is a twin boiler combi-pack.

One boiler is for heating, and a Rinnai Infinity continuous flow supplies the hot water. This solution can solve the temperature control issue.

So is there now an argument for the government think tank to broaden its brief to avoid the increased carbon footprint caused by fitting all those extra TMVs?

Several would be required in every house covered by the proposed amendment to Part G. With the approval authorities classifying our own Infinity range as exceeding all the requirements for safe temperature control, why not use a virtual TMV instead?

Geoff Hobbs in managing director
of Rinnai UK