What to do with Hot Water?

[docjames]

Have already consulted Dr Google but no decent answer given.

When I go away, I turn the hot water off. But i've been thinking more and more as my time away varies from 1 day to 1 month

Where is the "tipping point" where you may as well leave the hot water on, vs turning it off and then reheating - as presumably it takes quite some energy to reheat the entire system vs keeping it to temperature?

Before the smarties say "get a gas instant hot water" - my house doesn't have gas (no mains gas in my area).

My current action is > 5 days away = switch off, < 2 days clearly leave on, but what about in between? Is 5 days an appropriate cutoff? And when you need the hot water upon return is important too i suppose as it would be cheaper to heat at night (off peak) but if you want a shower as soon as you get home that's a problem too. I guess to keep the thread on track let's say I have time to wait for the system to heat (irrespective of time of day).


Geez I need to stop wasting brain cells on stuff like this.


Mods - feel free to move to playground if you think more appropriate but i am serious (dont call me shirley).

 

[Mal]

My brain can't calculate it based on your system. But model and capacity would affect the end result.

 

[Fantic125]

I would suggest getting in touch with your electricity provider and ask them the question; what is the off peak power consumption for a 24 hour period compared to heating the HWS from cold (being able to give them the make, size and model of the HWS of course).

 

[nickykim]

Used to have this discussion with my mother 35 odd years ago. Certainly not efficient for under 24 hours as the four teenagers proved to their mother at the time!

 

[happy2]

Questions like this make me so happy that I am on natural gas

 

[TiredOldFlyer]

What to do with Hot Water :

Sit on the fence and just turn the thermostat down

 

[harvyk]

Before the smarties say "get a gas instant hot water" - my house doesn't have gas (no mains gas in my area).

No but you could always get solar...




On a more serious note, I might consider turning off our HWS (although it's gas) if we were away for more than a month, but anything less than that I probably wouldn't bother, as it is always nice to have a shower after arriving home from a trip, and whilst I think about it, my family (grandfather) owns a house down near Batemans Bay, when we first got it we where vigilant about turning off things like the fridge and hot water, however after a couple of years we stopped bothering about such things, probably because it was decided that the small cost of the electricity far outweighed the annoyance of turning up there with a warm fridge and no hot water, and neither of those problems would be truly rectified until the next morning even once turning the power back on.

There are times where that house remains empty for a month or two at a time. (not often anymore)

 

[Mwenenzi]

For me I leave on if less than 10 days, based on an assumed thermal loss of 10%.
I have off peak electricity (separate meter), so if the trip allows do not turn on until 21:00.

[ENGINEER]
Temperature drop depends on the insulation & heat loss per hour (surface area is important)
In years gone by I used to do such engineering calculations with a slide rule & pencil. Now we can do with a finite analysis program [STRAND or equal] That's what grad engineers are now for now.
[/ENGINEER]

 

[samh004]

Isn't there an issue with turning off hot water systems and the bacteria that can grow... Legionnaires’ disease or some such?

 

[harvyk]

Isn't there an issue with turning off hot water systems and the bacteria that can grow... Legionnaires’ disease or some such?

I would imagine that once the water gets back up to temp, any bacteria which grew in there would be quickly killed, otherwise HWS would be a breeding ground for such things.

 

[docjames]

The best outcome would be for it to break right around the time gas gets installed in our area.....

Hmm, seems there's no real answer.

 

[medhead]

Solar, I would suggest.

 

[TonyHancock]

Make yourself a nice cup of tea with it and it will help your thinking process.

 

[UP4014]

Depends on if it is set as as off peak or re-heat when it get below a certain temp.Off peak I wouldn't be so worried about as power is cheap for that, but if the other pays to turn it off even for a night.

 

[The Rok]

Get solar, sit back, have a beer in the lounge and forget about it.

 

[docjames]

Haha, looks like it's solar ftw.

What do i do for the 4 months in melbourne there's no sunshine.....

 

[TiredOldFlyer]

Haha, looks like it's solar ftw.

What do i do for the 4 months in melbourne there's no sunshine.....

Move to Queensland.

 

[Austman]

Our apartment building (in Melbourne) uses Stiebel Eltron instant electic heaters. They are pretty impressive German technology and as they use 415V they really can heat instantly! You never run out of hot water.

DHE Instantaneous 3 Phase Water Heaters|DHE Water Heaters - Stiebel Eltron

 

[The Rok]

Our apartment building (in Melbourne) uses Stiebel Eltron instant electic heaters. They are pretty impressive German technology and as they use 415V they really can heat instantly! You never run out of hot water.

DHE Instantaneous 3 Phase Water Heaters|DHE Water Heaters - Stiebel Eltron

Can't see many houses having 415V though.

 

[munitalP]

@the rok - I have 415

[ELEC ENG]

Leave it on for anything under 3 weeks or so. The energy required to reheat a 120L well insulated hot water system will outweigh your "maintain temperature" cost based on ~ 10.4 c/KWh tariff (SYD area)

Additionally most newer systems have a "Vacation" setting where the temperature is allowed to drop to a better sustainable level that uses less energy to maintain "above cold" temperature, but the energy expired to reheat the water back to operating temperature (OT) sometimes outweighs the savings.

Remember, the highest energy use is bringing the water to the OT not maintaining it

[/ELEC ENG]