Every week we have clients asking why we are required to install a TMV or tempering valve to their hot water system. The short, simple answer is because it’s the law.
The longer answer is because it’s about safety. A TMV or tempering valve reduces the risk of scalding. This is because storage type gas, electric, solar and heat pump systems are storing hot water at between 60° C and 75° C. You need to be aware a severe hot water burn can occur in one second when the water is delivered at 60° C or higher. Hot water burns like fire because:
- At 60°C, a severe burn can happen in 1 second
- At 55°C, a severe burn would take 10 seconds
- At 50°C, a severe burn would happen after 5 minutes
What is a TMV?
TMV or thermostatic mixing valve installed by Whywait Plumbing
A TMV is a thermostatic mixing valve but is commonly referred to as a TMV. The role of a TMV is to mix hot and cold water together to provide you with hot water delivery at your tap that is at a consistent temperature.
When we install your TMV, we set the temperature to deliver the hot water in all bathrooms at 45°C in aged care or childcare facilities or 50°C in all other bathrooms.
A TMV is compulsory for use when used in common areas for aged care or childcare. A TMV is very accurate and very responsive to fluctuations in incoming water temperatures keeping the temperature to within 1° C of the temperature that it has been set at when we install it.
Accuracy of temperature in the TMV is delivered by a thermally sensitive element which expands and contracts in response to the temperature fluctuations of the incoming cold and hot water. This expansion and contraction regulate the temperature by controlling how much cold water mixes with the hot water. An added safety feature of a TMV is that if cold water flows become too low, they shut down to prevent 60°C plus water being delivered.
What is a Tempering Valve?
Non-compliant tempering valve installation connected with flexihoses replaced by Whywait Plumbing
A tempering valve’s role is also to mix hot and cold water together to provide you with hot water delivery at your tap that is at a consistent temperature.
The tempering valve is a simple three-way valve that is temperature actuated to mix the hot and cold water. These days most come preset at 50°C and when we install them, we test them by measuring the temperature of the water from your hot taps in the bathroom.
A tempering valve is commonly used in residential homes as a one-off valve at the hot water service. A tempering valve is slower to respond to temperature fluctuations compared to a TMV plus it will deliver water to within 3°C of the temperature that it has been set at when we install it.
Which Valve do you Require?
The Plumbing Code of Australia in AS/NZS 3500.4:2018 is very specific about water temperature is section 1.11, which states:
- To avoid the likelihood of legionella bacteria growth, an installation shall store water at a temperature of not less than 60°C
- All new heated water installations shall deliver heated water not exceeding 45°C for the aged, the sick, children or people with disabilities in healthcare, aged care, early childhood, schools and nursing homes. For all other situations, heated water shall be delivered not exceeding 50°C.
Ultimately when we are installing a temperature control device, we are legally obliged to comply with the requirements above and much more as they are prescribed in AS/NZS 3500.4:2018.
Overall a TMV is more expensive to install initially compared to a tempering valve. However, a TMV has a much longer working life span compared to a tempering valve as they are more accessible to service and replace the working parts. A tempering valve, by comparison, is usually just replaced when it stops working as they are not easy to service or replace parts in.
In Queensland, all work undertaken on a TMV or tempering valve is reportable to the QBCC and must have a compliant Form 4 submitted. For your protection always demand a copy of your Form 4.
Perception is reality and nowhere is this truer for us at Whywait Plumbing than when dealing with the issue of hot water temperature and the possibility of a serious hot water burn.
Everyone has a different perception of how hot they want their hot water whether it is for cleaning or sanitation or personal hygiene use.
Recent research in the United States from the Johns Hopkins Bloomberg School of Public Health, confirms hot water heater temperatures are too high.
In Australia, most manufacturers preset the thermostats for hot water heater temperature at 60-65 degrees. This is dangerously high for a significant proportion of homes, presenting a scald hazard particularly for young children and the elderly. This is because literally hot water burns like fire because:
At 60°C, a serious burn can happen in 1 second
At 55°C, a serious burn would take 10 seconds
At 50°C, a serious burn would happen after 5 minutes
It is estimated a serious hot water burn causes an estimated 1,200 hospital admissions and 50 deaths per year. Young children and elderly adults have thinner skin which burns more quickly putting them at increased risk.
In Queensland, it is the law that hot water delivered to bathrooms used primarily for personal hygiene purposes be regulated by use of a tempering valve or a thermostatic mixing valve that does not exceed 50°C. This is due to the fact that in 1995 the laws were changed requiring tempering valves to be installed on:
all new homes having a hot water system installed
replacement or upgrading of an existing hot water system
or when moving an existing hot water system to a new location on the property
However, homes built before 1995 will frequently still have hot water being delivered at 70°C. It is estimated that 37% of homes still have older electric or gas heaters delivering hot water that presents a scald hazard that will cause a serious hot water burn in one second.
Frequently these homes are rental properties. Many landlords and real estate property managers are unaware that recent litigation has placed a ‘deed of care’ onus on them to ensure the safe delivery of hot water in domestic bathrooms used primarily for personal hygiene purpose.
The installation of a tempering valve is an acceptable solution to hot water scald prevention. Delivering hot water at a consistent temperature is difficult without a tempering valve. This is due to the fact that as a hot water tank is depleted through use then replenished and reheated, the water temperature will not be constant throughout the tank.
Despite a perception by many people, a hot water service thermostat is not designed to provide precise estimates of water temperature. Its purpose is to begin heating when the temperature drops below a set level and turn off when it reaches a set level. Without a tempering valve installed it is almost impossible to assess the exact temperature of hot water delivered from a tap.
The advantage of a tempering valve is that guesswork is eliminated as tempering valves are designed to blend hot and cold water to deliver mixed water at a constant temperature and thus reduce the risk of a serious hot water burn.
Unfortunately for plumbers, property managers, homeowners and property investors hot water has increasingly become a legal minefield with the duty of care provisions.
It is for this reason Whywait Plumbing recommend that you install a tempering valve and maintain it compliantly with annual testing.
The recent outbreaks of hot water Legionella in Queensland mainly in hospitals is of concern. These, for the most part, were warm water systems which are not the same as your home hot water storage tank.
With hot or warm water systems there is always some risk but every system checked in recent weeks by Whywait Plumbing has had hot water temperatures that virtually eliminate all risk. However, there is almost no risk of you or your family contracting Legionella bacteria as a result of it breeding in your home hot water system.
Legionella Transmission Via Hot Water
Legionella transmission is airborne via respiratory droplets containing the bacteria. Warm water and domestic hot water systems that are contaminated will generally see the transmission of the bacteria in a shower that has not been used for a period of time.
Hot Water Preventative Measures For Legionella
Hot water systems should be maintained so that water at the point of use at any tap or outlet is 50°C or more after having been turned on for one minute.
Hot water systems should not be used until they have reached 50°C especially if they have been turned on for any period.
Generally, domestic hot water systems should have a temperature of 60°C or higher in water leaving the hot water storage tank.
DO NOT turn down the thermostat on an electric hot water storage tank to below 60C.
Hot Water Temperature For Preventative Of Legionella
Hot water systems should be maintained so that water at the point of use at any tap has a temperature that affects the survival of Legionella as follows:
- Above 70 °C – Legionella dies almost instantly
- At 60 °C – 90% die in 2 minutes
- At 50 °C – 90% die in 80-124 minutes, depending on strain
- 48 to 50 °C – Can survive but do not multiply
- 32 to 42 °C – Ideal growth range
- 25 to 45 °C – Growth range
- Below 20 °C – Can survive but are dormant, even below freezing
What Is Legionella Bacteria or Legionnaires Disease
What it is:
- Caused by the Legionella bacteria, commonly found in creeks, ponds and soil.
- Rare in people under 20 years, with those over 50 years old who smoke or have a weak immune system particularly susceptible.
- Non-specific flu-like symptoms including fever, headache and muscle aches, developing within a week of breathing in the bacteria.
- Usually progresses rapidly with pneumonia symptoms, high fever, shortness of breath and chest pain typical.
- A person with the disease usually needs to be admitted to hospital for antibiotic treatment and care.
- Early diagnosis and antibiotic treatment important, and those treated usually begin to improve with three to five days.
Testing Your Storage Tank
For most homes, there is a very little risk of you having hot water legionella occur in your hot water storage tank unless you do really stupid things such as turn off your heating source.
An easy test of the storage temperature is to get a thermometer and test the temperature of your water from the overflow relief valve drain.
If you have any doubts about the temperature in your storage tank contact Whywait Plumbing to organise a service call to check your hot water system.
Judging by the number of phone calls in the last few days to Whywait Plumbing there is genuine concern amongst our clients over the threats posed to them from Legionella risk in their domestic hot water systems.
We can assure you whilst there is always some Legionella risk, there is almost no risk of you or your family contracting Legionella bacteria as a result of it breeding in your home hot water system.
The outbreak of Legionella bacteria in the hot water system at Wesley Hospital that killed a 60-year-old cancer patient and left a 46-year-old woman seriously ill has minor ramifications to be sure because all hot water systems can pose a risk.
That potential risk is why Whywait Plumbing is constantly advocating appropriate maintenance on your home hot water system to minimise that risk even further.
However, there is a huge difference between your home or domestic hot water system and the warm water recirculating system at Wesley Hospital. The Legionella outbreak in their warm water system has not been as a result of contamination in the hot water storage system or the hot water pipes but appears to be literally at the point of delivery from the shower where the water is cooler.
A warm water system is vastly different to your home hot water system with Wesley’s water temperature set between 42.5°C and 43°C. This is lower than the maximum 45°C legislated in the Plumbing and Drainage Act for hospitals. This low-temperature setting is a result of guidelines from Queensland Health that dictate hot water temperatures in hospitals be reduced to avoid the possibility of serious burns to young children and elderly patients. The downside of this requirement is that the possibility of Legionella bacteria surviving in reticulation pipes is increased. Water temperatures of around 46°C will kill legionella bacteria.
Warm water systems are typically found in care facilities, such as nursing homes, hospitals and child care centres, where water for purposes such as bathing and cleaning is provided at approximately 45°C to prevent scalding.
Your home hot water system if it is a storage tank is heating the hot water to between 60°C and 70°C. If you have a tempering valve or thermostatic mixing valve (TMV) installed then that has been set to deliver hot water at 50°C at each individual tap.
If you have no tempering valve installed, you virtually have eliminated all risk. But you have increased the risk of someone suffering a scalding from hot water. As always it is about managing risk.
However, there is an urban myth prevalent that you can reduce electricity costs by turning the thermostat down on an electric storage unit to 50°C. This is not recommended for many reasons but it will not save you electricity and to physically get a thermostat down that low requires physically breaking the locking mechanism on it that allows the setting to be between 60°C – 70°C. If you want to lower the delivery temperature the only acceptable and compliant method is to install a tempering valve.
In 99.99% of cases, the temperature ranges your hot water system operates in is almost certainly killing any Legionella bacteria. The risk if any, is after the storage tank in the reticulation pipes. By turning your shower on and running the tap with hot water first then cooling down with cold water to your desired shower temperature you are virtually eliminating what risk there is.
What the outbreak at Wesley Hospital has confirmed is that there is a risk from warm water and that maintenance of your hot water systems will manage and eliminate that risk.
What Whywait Plumbing do recommend is that you take advantage of our ongoing reminders and offers to service your tempering valves. This not only ensures that water is being delivered at 50°C but eliminates any possibility of Legionella. It also ensures you are complying with the requirements of most insurance policies in ensuring that routine maintenance is undertaken plus we provide you with a written report and a form 4 compliance certificate that is further evidence of your hot water unit being compliant.