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Comment by dfc | Hacker News Reader

Nest folks, once you are happy with your thermostat product please pivot to water heaters. There is no reason why I heat the water in the tank up throughout the night. I think that my household demand for hot water is fairly predictable with spikes in the morning for showering and in the evening for dishes and laundry.

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I've considered doing this manually, but when I ran the numbers, it barely saved anything, at least if your water heater is insulated to modern Energy Star standards. In the past decade or two, standby losses have been brought down so low that they're almost negligible compared to actual hot-water usage, e.g. one shower will take more energy than a whole month of standby heating.

When I looked into it in my own case, it worked out to slightly under 1 kWh/day in standby losses, or about $2/month. I turned off the water heater when I was gone for a month once, and the savings do seem to have been in the noise somewhere. Assuming a Nest-like device to do that for me would cost the same ~$250 that a Nest does, it would take 20 years to recoup the cost of the device, even assuming it was so perfect that it saved all standby losses.

Nice. How did you estimate the standby costs? I wonder if gas v. electric makes a difference? Any chance you live in a colder (40 degree basement in winter) climate?

In general, there's a good reason for heating the water overnight: electricity is often cheaper at night, and (on a national level) it means that electricity demand is spread more evenly over the whole 24 hours.

This is a good idea, but are you by chance located outside the US? Every water heater I've personally encountered in North America has been powered by natural gas. Even so, it only takes an hour or so to fully replenish the hot water, so it still makes sense to allow the water to cool down between, say, midnight and 5am.

Huge swaths of the U.S. simply don't have natural gas. The township that I used to live in explicitly stated in their planning that they did not intend to run gas lines.

My current place doesn't have gas either...

Yeah, I'm in New Zealand.

Electricity is cheaper at night (from some utilities) because the demand is a lot lower at night. But why is it a good idea to heat water at night when I'm not going to use it?

And as others have pointed out I have a natural gas heater.

also residential customers usually do not have hourly rates, rather fixed per kWh monthly ones.

Have you thought about switching to a tankless hot water system?

So I can spend $2800 on a water heater that has questionable reliability, requires a bigger gas line, and will save me 40% off my $18 a month water heating bill?

Yes. I've thought of it, but no, it is not a good idea.

I think your pricing is a little off; my parents have had a Rinnai heater now for more than several years with no reliability issues and spent far less than $2800. Even Amazon has them priced much lower [1].

1 - http://www.amazon.com/s/?ie=UTF8&keywords=rinnai+water+h...

This looks like a good resource on the topic:

http://michaelbluejay.com/electricity/waterheaters.html

Virtually everyone modern home has thermostats, but far fewer households have dumb water boilers.

There is no reason why I heat the water in the tank up throughout the night

Aside from the fact that you need the water to remain above a certain level or the water can become dangerous (e.g. legionella), what happens the night you play glow in the dark flag football and decide to take a shower? Or do a load of dishes? Etc.

The Nest "works" (in the absolutely marginal way that it does so) because it makes a middling difference. That would be a stark difference with a hot water tank.

What happens the night i stay up late with the nest and want the heat turned up?

My dishwasher contains a heating element and so does the clothes washer.

What happens the night i stay up late with the nest and want the heat turned up?

Put on a sweater? But yes, what you describe is exactly how many people with Nest thermostats end up disabling the "intelligent" functions.

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