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Is Your Condo in Hot Water?

Is your hot water safe?  Too hot and you can be seriously burned.  Not hot enough and your hot water many harbor dangerous bacteria.  What is the ‘correct’ temperature to set a water heater?  It is a complicated question widely debated as ‘correct’ depends if you are concerned about energy saving; good heath; or safety.

From an energy conservation point of view the Department of Energy’s (DOE) recommendation of setting the temperature at 120 degrees is the answer, as it is also a much safer temperature to avoid scalding accidents.  However the health industry recommends 140 degrees, as this setting is needed to kill Legionella, the bacteria causing Legionnaire’s Disease killing 10 percent of those who become infected.

People can contract the disease by inhaling droplets of water containing the bacteria.  Most of the reported outbreaks have occurred in large institutional structures (hotels and hospitals) and multifamily dwellings served by central water supply.  Several cases have been traced to evaporation from large cooling towers.  The Legionella bacteria can grow in any water environment in which the temperature is too low to kill it, making it a potential risk in single-family condo units as well, hence the debate over hot water heaters.

At 140 degrees, Legionella dies within about 30 minutes while at 130 degrees it takes 6 to 8 hours for the same result.  At the typical 120 degree setting, the bacteria will survive but not multiply.  Below 120 degrees the bacteria thrives.  These environmental health numbers then need to be weighed against the fact it takes 10 minutes for water heated to 120 degrees to cause a serious burn while it only takes 6 seconds of contact at 140 degrees.

The dilemma is the most susceptible to the disease, namely, those with chronic respiratory disease or a compromised immune system are the most likely to be scalded by water at 140 degrees.   Adding to the problem is DOE’s estimate of households can reduce energy costs by 10 percent by turning the water temperature down to 120 degrees from 140.  So what’s a responsible property manager or unit owner to do?

One could argue the risks of contracting Legionnaire’s Disease is small as only 18,000 cases are reported annually in the United States compared to its population of 326 million.  However, it you do not want to make this risk-benefit decision you could install temperature-regulating devices either on the water heater or individually on any taps used for washing or bathing.  A thermostatic mixing valve attached to the water heater injects cold water into the heated water coming from the tank, allowing you to set the tank temperature higher than the water that comes out of the shower or sink faucets.  Water tempering-pressure-balanced valves attached individually to the faucets adjust the ratio of hot to cold water coming from the taps to maintain the temperature you select.

Although thermostatic valves are more expensive – from $150 to $250 compared to less than $50 for some tempering valves – you only need one valve for the water heater, while you will need a tempering valve for every faucet to be regulated.  Thermostatic shower valves provide increasingly popular options for unit owners.

Though low water temperature is the primary problem in controlling the disease’s appearance, a disease friendly environment can be created when non-moving water sits in pipes for prolonged periods or if sediment is allowed to collect at the bottom of aging water tanks.  Therefore the following risk management steps should be taken:

  • Properly insulate pipes to prevent overnight cooling
  • Identify and remove abandoned sections of the plumbing piping system
  • Minimize the use of rubber, silicone, and plastic gaskets in plumbing to eliminate a source of nutrients for bacteria growth
  • Treat hot water tanks with chlorine as you would with swimming pools and fountains
  • Periodically flush the pipes and water tanks of condo units vacant for prolonged periods

With many condo units in Maine hosting ‘snow bird’ unit owners and other types of transient occupants, it is important consistent water temperatures are maintained when residents leave their units for vacations or extended travel.  Also remind unit owners upon their return to turn on their faucets for several minutes to clear them of contaminants.  Keep in mind flushing hot water tanks periodically not only removes sediment prolonging the tanks useful life but provides more efficient hot water heating as the heating elements do not become coated.  With a little care you can keep your condominium out of hot water.


Article written by Jack Carr, P.E., R.S., LEED AP, Criterium Engineers

Published in Condo Media, November, 2018

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