Comment by waste_monk | Hacker News Reader

Comment by waste_monk | Hacker News Reader

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>(And, apparently, as I learned, there's a mixing valve at the hot water heater: i.e., the hot to the shower is not direct from the water heater, like I had imagined. We raised the temp there, slightly.)

When we changed from instant hot water to water tank + heat pump, the guy said the tempering valve was a safety thing (IIRC ours was set to 60 degrees Celsius by default, but could go up or down about 10 degree either way). That is, if you accidentally step in the shower with only hot water on you'll still hurt yourself but the damage will be limited to "strong profanity and aloe vera" instead of "you've won a stay in the burn ward".

Although saying this, I did a quick bit of research and found that 60 may still be too high [1]. I have an IR thermometer so I think I'll measure the temperature of my shower (after any loss from pipes etc.) and see if the tempering valve needs adjusting down.

[1] mild nsfw - image of scalded foot https://whywait.com.au/a-serious-hot-water-burn-occurs-in-on...

"Safety" is also what my guy said. The problem is that in isolation the answer doesn't make any sense: why should I be heating water up to then re-mix cold water? Is that not a waste of energy?

The fuller answer, I think, is that the "raw" hot line additionally goes towards uses that can take scalding water, one or more of the dishwasher and the laundry, depending on whether you have either or both of those in your dwelling. (I hadn't thought of those, since my concern was on the shower. I also can't see the piping, in my place, so it was a black box of sorts.) For uses that might interact with a human, then it's a safety thing, then it makes sense to do the mix with cold. (I believe the other line, the shower bound one, is called the "tempered hot" line.)

My guy also refused to raise it too much, or disable it altogether, citing codes and that it couldn't exceed like 140℉ or so. Which was fine, really, since I was asking for it to exceed 95℉…

Storing the water at a higher temperature effectively increases the capacity of the tank. Also the stored hot water has to be above a certain level (~60 degrees) at least some of the time otherwise it won't prevent any bugs growing in it.

Yep... particularly Legionella Pneumophila and friends which can cause Legionnaire's disease.

I was taught as a child NEVER to use a hot shower from a water tank or drink warm water from the tap after a sustained power outage until the tank has had time to come back up to it's normal temperature... Legionnaire's can straight-up kill you via pneumonia.

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