Comment by alex3305 | Hacker News Reader

Comment by alex3305 | Hacker News Reader

I have a warm water boiler / water heater where I live now. Running fully on electricity, which I have 'made smart' with Home Assistant. First of all I replaced the analog temperature sensor with a digital DS18B20 connected to a Raspberry Pi. I 'calibrated' this sensor with another sensor at our main faucet in the kitchen, so I can set the tap water temperature. Secondly I've added a power monitoring smart socket to the water heater, so I can switch it remotely. Finally I've added both to Home Assistant as a climate device, so I can easily control it.

Simply put I've set it up that during electricity peak times the boiler doesn't try to heat water to save on electricity costs. Heating water is all done in the off peak hours with some easy calculations. Also I tend to set my boiler to a lower temperature (ie. 58 degrees) during weekdays and higher (60+) during weekends or holidays. That way I always have hot water and get rid of legionella growth.

What I can see I'm using about 1.5 - 2kWh a day for keep 100 liters of water at at least 55 degrees. While the manufacturer of the water heater says the device should use between 7 and 9kWh a day. I really would like to optimize it any further, but it seems that I've hit a wall.

One additional data point: on my heat pump the economy setting for hot water production starts heating once water cools to ~42C (truly, a universal answer) and heats it up to ~55C. As for anti-legionella, once a week there's a cycle where the top setpoint is raised to 65C.

There are heat pumps to replace warm water boilers, but if you are only using 2kWh a day, it's probably not gonna pay off in a long time.

If you're in the US. Starting next year, the Inflation Reduction Act added a $1900 tax credit for purchasing heat pump water heaters so it might pay off earlier than you think.

Yes. I know of these. Here in the Netherlands those start at about 1000 euro's for a hybrid solution. A full heat pump boiler starts at about 2000 euro's. But you get about 600 euro's subsidy. However, as far as I can tell it will only about half my power consumption for hot water. So with the current electricity prices (about 30ct/kWh) it will pay back itself in about 13 to 15 years or so.

I've also looked at instantaneous water heaters, which could be even more efficient. But those with enough capacity need 400V, which I don't have in my apartment. Also I would probably have legionella growth in my regular water heater if I want to save even more electricity. Which would be a health issue.

That depends where the hot water heater is located.

In my case, I was able to get rid of my dehumidifier in the basement and the window unit in the summer. Paid for itself in ~6 months.

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