Sorry for using this comment as a way to get ahold of you but there is no DM function on HN and the comment I was wondering about was posted by you 18 days ago and the comments are locked now.
I have been controlling my water heater with HA for a few months and I too am risk averse when it comes to legionella. You have taken it to another level by replacing the sensor inside with a DS18B20. I was also interested in doing this but I don't really want to drill into it. How did you install the sensor? Is the water not under pressure? I've just measured water temperature at the tap with a meat thermometer and under flow into a container to determine that the temperature falls in the range that is safe for legionella growth. Would love to look into a proper sensor again if you have any information about that.
Again, sorry for hijacking your completely unrelated comment.
First of all, I'm also concerned by legionella growth. However all the sources I can find suggests that at a legionella run above 60 degrees celsius once a week should be enough to kill all bacteria. So that's what I'm doing.
My sensor installation was extremely easy. My warm water heater is in fact a barrel within a barrel. And some insulation material between those barrels. If it would only be metal, you lose too much heat. In the outside barrel (excuse me for lack of a better term) there was an analogue thermometer. This thermometer has a metal back so it makes direct contact with the inside barrel. I just pulled this one out and replaced it with a DS18B20 probe. Again metal against metal, so maximum contact.
Finally I have calibrated the sensor by running it with hot water at the tap and measuring the temperature both there and on the warm water heater (with 2 DS18B20). I've done this for several temperatures with intervals of 10 degrees. I've ignored possible sensor deviations. Finally I used Excel's INTERCEPT and SLOPE functions on the range to calculate the value needed for a linear equation. I have used the formula:
boiler_temperature * SLOPE + INTERCEPT
My math is probably far from perfect and I might revisit it one day. But it works for me currently. I also visualized the measurement results with my calculations and they seem to be pretty accurate. Especially when accounting for missing measurements.
I've also added my personal page to the 'About me' on here, and I have the same Reddit username if you want to DM me there.
Sorry for using this comment as a way to get ahold of you but there is no DM function on HN and the comment I was wondering about was posted by you 18 days ago and the comments are locked now.
Here is the comment in question: https://news.ycombinator.com/item?id=33347058
I have been controlling my water heater with HA for a few months and I too am risk averse when it comes to legionella. You have taken it to another level by replacing the sensor inside with a DS18B20. I was also interested in doing this but I don't really want to drill into it. How did you install the sensor? Is the water not under pressure? I've just measured water temperature at the tap with a meat thermometer and under flow into a container to determine that the temperature falls in the range that is safe for legionella growth. Would love to look into a proper sensor again if you have any information about that.
Again, sorry for hijacking your completely unrelated comment.