How Hot Should My Hot Water Be?

Dear Home Ec 101,

Yesterday you posted about running the hot water before running the dishwasher. I see a lot of save money and be green by turning down the temperature of your water heater. What temperature is the right temperature? Will having my water heater set at 110°F make finding that sweet spot in the shower less of a hassle?

Spring Showers Bring May Flowers

Heather says:

Do not set your shower to 110°F. Your water heater should be set between 120°F and 140°F.

Anything below 120°F and runs the risk of setting up a bacterial resort spa. The risk is small, but Legionnaire’s Disease can be fatal.

Legionella, the bacteria responsible for Legionnaire’s disease causes pneumonia and is most easily contracted by the elderly or those with compromised immune systems. This disease isn’t acquired by drinking water, but by aspirating it or inhaling it in the fine mist associated with shower spray.

Anything above 120°F has a scald risk. Water right at 120°F doesn’t carry a scald risk, but 125°F can scald in less than two minutes. If you have small children or elderly family members in a household, err on the side of closer to 120°F.

If your home is on a crawl space or has exposed pipes, be aware that insulating your pipes does more than simply save energy. Water loses heat as it travels through your plumbing. If there are pools of water sitting around at temperatures below 120°F bacteria can grow. Insulating your pipes helps water stay hot enough to flush any potential bacteria from your pipes with normal use.

TL;DR Set your water heater between 120°F and 140°F, this balances the need to keep water at a safe temperature to prevent scalds and not roll out the bacterial welcome mat.

Insulating your water heater helps prevent heat loss and conserves energy.


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