Personal Choices for Sustainability: A Tankless Job

As part of our townhouse remodel, we had a tankless water heater installed. Its predecessor was a gas water heater whose life expectancy was 15 years. Ours was 20 years old. So rather than awake one morning to the prospect of a cold shower, we preemptively had a new water heater installed.

As a company, Autodesk is doing everything it can regarding sustainable design. The Sustainable Materials Assistant for Autodesk Inventor is available as a technology preview on the Autodesk Labs site. The Autodesk corporate web site has a full section on sustainable design. So it made sense to us to select a tankless water heater. The premise behind tankless water heaters is that energy is saved by heating the water as needed rather than heating and maintaining hot water at the ready.

1. The first piece of the puzzle is a new gas line. To heat water quickly and as it flows requires a dedicated line. Our new line is 0.75 inches in diameter.
   

2. Our unit is a Noritz N-0751M-DVC. It is an indoor wall-mounted unit that vents to the outside. It has no pilot light using a direct ignition mechanism instead. It operates at 15 to 150 psi. The water holding capacity is only 0.2 gallons. It can increase the water temperature up to 45 degrees with a flow of 7.5 gallons per minute.
   

3. The initial factory temperature setting is 110 degrees Fahrenheit. Out of the box, the controls allow you to set a desired temperature between 100 and 120 degrees. At 110, we found that our water was not hot enough and took quite a while to reach a usable temperature. So we tried 120 degrees. That still seemed to take longer than desired. The Noritz unit has override controls that let the owner increase the upper limit to 140 degrees. After setting the override, we have our temperature set at 125 degrees. We do not have young children and the accompanying worry that they might inadvertently scald themselves. With our son at boot camp, we are what they call empty nesters.

Despite having the setting at 125 degrees, it still takes quite a while [1 minute, 11 seconds at full blast or about 3 minutes on normal flow] for hot water to reach our master bathroom faucets. I have resorted to brushing my teeth with the water running, a wasting water no-no taught to us as children, so that I have hot water for shaving by the time I am done with my teeth. Apparently, the tankless water heater trades off increased water consumption for lower energy costs. This is a viable strategy until the day comes when the cost of clean water (a scarce commodity) outstrips the cost of energy (e.g., solar). Recall that we installed a solar water heater in our first house in 1982. So given the long-term prospects, I cannot recommend tankless water heaters at this time. Water is predicted to eventually be so scarce that its discovery on the moon is now being celebrated. We could supplement our household unit with a smaller on-demand unit specifically located at the sink where I shave, but that may come at a later day.

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