Between the code changes to ICC and IAPMO, there definitely is a conundrum regarding the setting of the temperature of hot water.

In some cases, there are those who would like the hot water set for a high temperature. There are others who want hot water to be set at a lower temperature. Plumbing engineers are asking, “What temperature do we use?” That is a good question that all the plumbing codes are struggling to determine.

The battle lines are between bacteria growth and scald prevention. Both are important, but both have different philosophies regarding hot-water temperature. Add to that the plumbing manufacturers trying to provide products that satisfy all issues.

One more point to enter the equation is the reduction in the amount of water being used. Some states already have lowered the shower and lavatory flow rates. Both fixtures have a demand for hot water. The shower flow rates are going from 2.5 to 1.8 to 1.5 to 0.75 gpm, depending on state requirements, green demands, LEED stipulations and just a common desire to save water.

When you lower the temperature of the hot water and lower the flow rate through a showerhead, you add stress to the pressure-balancing valve or thermostatic mixing valve. I developed a spreadsheet to show the impact on shower valves. It was rather revealing when you think about the demand on compensating shower valves.

Plumbing engineers have preferred running hot water at a temperature around 117° F. This is listed as the pain threshold temperature, hence safe for use in any fixture. If you use that temperature of hot water and a cold-water temperature of 55° with a 1.5-gpm showerhead, the amount of cold water required is 0.34 gpm. If you lower the flow rate to 0.75 gpm, the cold-water demand is down to 0.17 gpm. Basically, compensating shower valves are being asked to add a minimal amount of cold water. Realize these shower valves are designed to flow 2.5 gpm.

If you lower the hot-water temperature to 110°, the amount of cold water required for a 1.5-gpm showerhead would be 0.19 gpm. If the showerhead is lowered to a 0.75-gpm flow rate, the cold-water demand drops to 0.095 gpm, which is next to nothing.

Getting to work

Water-heater manufacturers are developing new point-of-use water heaters that can deliver hot water right at the temperature needed. This will be great for lavatories, bathtubs and similar fixtures. For showers (and most likely bathtubs), these newer water heaters will be closer to delivering 120° water. The 120° is the maximum temperature permitted from a shower valve or bathtub filler. This temperature also reduces the stress on a compensating shower valve.

By having a point-of-use water heater, you reduce the amount of piping to a fixture, thus reducing the amount of potential bacteria growth in the piping system. Point-of-use, controlled-temperature water heaters also reduce the scalding potential for plumbing fixtures.

Some of the experts on Legionnaires’ disease have expressed a concern about water heaters with a lower temperature set point. Claims of 131° to 140° are being indicated for all water heaters, whether point-of-use or centrally located. The thought process is to kill any bacteria that may grow in a water heater.

If water heaters have the temperature raised to 140°, the question is whether the code should regulate the temperature of the water in the hot-water piping system. If you raise the water-heater temperature, you can lower the piping temperature with a thermostatic mixing valve. Does that result in the potential for bacteria growth in the hot-water piping? The answer is yes.

The concern is how to deal with bacteria growth, scald prevention and water savings all at the same time.

Look to the Swedes

I had the experience of reviewing a Swedish system for hospitals that addressed all three issues by raising the water temperature to above 140° in the middle of the night and bleeding off a minimal amount of flow at each fixture for a period of 20 minutes. It does waste water during the bleed process. Of course, this required each fixture to be electronically controlled with sensors going back to the main control panel. It also required sensors throughout the piping system to allow the flow and discharge at the required temperature. For the remainder of the day, the hot-water piping system was set to 117°.

Even with this elaborate system, when you lower the flow rates through a showerhead to 1.5 gpm or less, the amount of cold water required to temper the hot water is still minimal. It still stresses the compensating shower valve.

It should be noted shower-valve manufacturers already are responding to the lower flow rates with more responsive shower valves. The difficulty is having a valve work well at 2.5 gpm and 0.75-gpm flow rates. The concern is a showerhead is easily changed at any time during the life of a building.

Cooks in the kitchen

Add to all this discussion the temperature of hot water for commercial kitchens. This temperature typically is regulated by health codes. Most health codes require 180° water for the final rinse of any dishwashing.

Interestingly, the 180° water temperature has been around for many years. Yet I recall in my college years a report that came out stating it is not the hot-water temperature but the sanitizer used during the final rinse that does the job of sanitizing the dishes. There have been many similar reports published over the years, yet these seem to be ignored by health codes. The philosophy is if the sanitizer fails we’ll get the dishes taken care of by the hot water. This is a belts and suspenders approach which often doesn’t play well with plumbing codes.

The other problem facing plumbing codes is that while the flow rates are not being lowered in the model codes, states and local jurisdictions are lowering those rates. In most situations, the states and local jurisdictions don’t realize the impact to the rest of the plumbing system. This is one of the reasons the model plumbing code organizations realize that need to address all these issues.

IAPMO is addressing many of these issues through the Legionella Task Group. ICC is addressing it through the code-change process. ASHRAE is doing it through its standards process. If you have any ideas, IAPMO, ICC and ASHRAE are listening. Look for changes in the near future to the plumbing codes and standards.

Think about ways to solve these issues.