A few weeks ago, Sarah and I traveled to spend Thanksgiving at the home of some of our extended family members.
The first morning we were there, I grabbed some clothes and headed for the bathroom to take a shower. Just like I do at home, I turned the hot water to full and turned on the cold water just a little bit, waited about fifteen seconds, and stepped in.
I actually thought I was going to scald myself. I turned down the hot water and turned the cold water up quite a bit until I found a good balance, then I enjoyed my shower.
Afterwards, I was talking to the person who was hosting us and I told him that I was impressed that they were able to take such hot showers. He told me that he, too, turns on a mix of hot and cold water for his shower, as does his wife.
This threw me for a loop, so I asked about their hot water heater and, upon discovering they had a tank-style heater, I was even more shocked. Apparently, my face showed surprise, so I asked him why they keep their hot water heater so hot.
The reason? Disease prevention.
For many years, our family has kept our hot water heater at around 120 F. This is in line with the Department of Energy recommendations as found on the EnergyStar website for saving energy on water: “Set water temperature only as hot as needed (110-120 degrees) to prevent scalds and save energy.”
We followed that to a tee. Our hot water heater produces water very close to 122 degrees Fahrenheit (50 C). I’ve checked it several times.
Functionally, that means when I would step in the upstairs shower and turn the water on to full heat, the temperature would be just about perfect for what I like in a shower. Sometimes, I’d have to turn it down just a little bit, but most of the time, full heat was perfect for me.
Naturally, I started researching the question and I came upon this article from the Canadian Journal of Infectious Diseases entitled Residential water heater temperature: 49 or 60 degrees Celsius?
It turns out that at about 50 degrees Celsius, which is what we keep our hot water heater set to, you have a drastically higher chance of Legionella living in your hot water tank. Instead, they recommend keeping it set at 60 degrees Celsius (about 140 F).
The problem with that temperature is that you run into some danger of scalding. The solution there is to have anti-scald devices at the faucets and showers in your home. Basically, such devices add a small amount of cold water to the hot water input at those faucets so that even the hottest water at the faucet won’t scald you.
After doing this research, I raised our own tank temperature up to about 140 F. We already had these anti-scald devices installed, so the water in the shower isn’t scalding, but it does come out warmer than I like, meaning I mix in some cold water with my showers.
We’ve been doing this for a few weeks now and I haven’t noticed a big jump in energy usage, though it’s hard to tell through the raise in energy use due to the onset of winter. Still, frugality isn’t worth the risk of a significant increase in the likelihood of Legionnaire’s disease or other bacteria-borne illnesses in our home. If it costs a few extra dollars per month, it’s still well worth it.