Hot Water Cylinders and Legionella

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KrazyKid

768 posts

Ultimate Geek

# 205540 17-Nov-2016 10:46

Can anyone point me in the direct of guidelines for NZ Hot water Cylinders and Legionella prevention

It particular I am wondering how long can I safely turn off a domestic hot water cylinder each Day. I assume since ripple control is common 12 hours on 12 hours off should be safe?

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2979 posts

Uber Geek

# 1672621 17-Nov-2016 10:55

Google is always your friend. Took around 5 seconds to find...

https://www.energywise.govt.nz/at-home/water/saving-money-on-hot-water/

Check your hot water temperature

It should be 60°C at the cylinder (to prevent the growth of legionella bacteria) and no more than 55°C at the tap so you don't get burnt (children are particularly vulnerable). Depending on your cylinder, you may need an electrician or plumber to adjust your thermostat. Even an extra 10°C on the thermostat of your hot water system could be costing you $25 a year with a modern cylinder, or twice that with an older one.

Nothing is impossible for the man who doesn't have to do it himself - A. H. Weiler

jnimmo

What does this tag do
1022 posts

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# 1672626 17-Nov-2016 11:11

Yeah 12 hours on/off will be fine as long as the base of the cylinder gets up to 60 degrees for one hour per day

KrazyKid

768 posts

Ultimate Geek

# 1672627 17-Nov-2016 11:13

Thanks for the replies

I am interested in turning off the cylinders for periods of time. Thus the temp is going to drop below 60 degrees.

I think I will save money by time-shifting the cost of the power to non-peak periods.

I also think (but have no evidence) it will be cheaper to only heat a cylinder 8-12 hours a day rather than maintain the temp at a constant level by heating all day.
My families usage is 2 showers in the morning and the kids baths/showers in the evening. I think that heating the water to temp for 4 hours on, 8 hours off could be cheaper
Having a modern well insulated cylinder should help with this second theory.

Does anyone have evidence that my 4 hours on - 8 hours off theory is correct?

nickb800

2298 posts

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# 1672629 17-Nov-2016 11:14

I think the question is more about duration and frequency rather than temperature - which is harder to google.

Based on the following, I'd think that 1 hour daily over 60degrees would be sufficient, plus however long it takes for the tank to reach 60degrees from its initial temperature

http://www.level.org.nz/energy/water-heating/solar-water-heating/solar-water-heating-storage-cylinders/

Controlling Legionella

Domestic hot water cylinders should reach a temperature of at least 60ºC daily to kill any Legionella organisms present. Acceptable Solution G12/AS2 Solar water heaters requires that systems are capable of heating the water to 60ºC either:

continuously, where the element is in the bottom 55% of the cylinder, or
once a day, where the element is in the bottom 20% of the cylinder, or
weekly, where all of the water within the system is heated for at least 1 hour (and the temperature is measured in the bottom 20% of the cylinder).

tchart

1534 posts

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# 1672639 17-Nov-2016 11:32

Sorry to hijack the thread but Im looking at turning our cylinder temperature down as its way too hot at the tap. At our old house (on gas) there was a knob you could turn to dial down the temp.

Our new (electric) one doesnt have a visible knob (seems to be behind a cover).

I looked in the manual and it says that only an authorized person can do it or warranty void etc

Is this just BS?

tchart

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# 1672649 17-Nov-2016 11:38

One person supports this post

Sorry just to answer my own question, on further inspection I apparently have a "tradesperson adjustable thermostats".

The reason its hidden behind a cover is that "removal of the front cover will expose 240 V wiring."

ubergeeknz

3344 posts

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Vocus

# 1672668 17-Nov-2016 12:00

tchart:

Sorry just to answer my own question, on further inspection I apparently have a "tradesperson adjustable thermostats".

The reason its hidden behind a cover is that "removal of the front cover will expose 240 V wiring."

That's pretty standard on electric cylinders. If it's drifted (got hotter over time) the thermo may be on its way out anyway, but worth a shot adjusting it first.

timmmay

15228 posts

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# 1672732 17-Nov-2016 12:43

One person supports this post

KrazyKid:

I am interested in turning off the cylinders for periods of time. Thus the temp is going to drop below 60 degrees. I think I will save money by time-shifting the cost of the power to non-peak periods.

I also think (but have no evidence) it will be cheaper to only heat a cylinder 8-12 hours a day rather than maintain the temp at a constant level by heating all day.
My families usage is 2 showers in the morning and the kids baths/showers in the evening. I think that heating the water to temp for 4 hours on, 8 hours off could be cheaper
Having a modern well insulated cylinder should help with this second theory.

I heat my water off peak, 1am to 7am, because I pay a lot less off peak with Flick electric. It saves me something like $1 per day, ie around $350 per year, based on current estimates, though that might be a bit high. If you have lower off peak rates then sure, give it a go. It cost me $250 for a digital timer installed my an electrician.

Modern cylinders keep water warm a long time, even after a week away when we came back the water was pretty warm. However if you use water throughout the day it will top it up with cold and slowly get colder.

A large bath takes a lot of hot water. If we have two adults shower morning and evening plus some dish washing and an occasional load of washing the water is plenty hot enough. On washing days, given we wash four loads with warm water, the cylinder needs to be on during the day. I actually have a 45 minute "top up" heat running in the afternoon as we have guests at the moment and it ensures enough hot water for the evening.

tchart:

Sorry to hijack the thread but Im looking at turning our cylinder temperature down as its way too hot at the tap. At our old house (on gas) there was a knob you could turn to dial down the temp.

Our new (electric) one doesnt have a visible knob (seems to be behind a cover).

I looked in the manual and it says that only an authorized person can do it or warranty void etc

You don't want to adjust the cylinder temperature, you want a mixing thingy (valve?) after the cylinder to mix in variable amounts of cold water. This ensures the bugs are killed but reduces the temperature at the tap. This was done by default for my new relocated cylinder a few years ago.

redmouse

69 posts

Master Geek

Subscriber

# 1672733 17-Nov-2016 12:43

Our hot water cylinder is on a timer, it switches on at 10am and off again at 4pm. We have PV solar and are trying to use free electricity to heat our water. The thermostat is set at just over 60c. Depending on hot water usage, the cylinder is usually at the desired temperature between 12:30 and 1:30 (I monitor this, it's still heating at the moment). Generally, it will not heat again during the afternoon. We shower in the evening (three people) and there is usually enough hot water for a quick shower in the morning. Our hot water element is only 2kW and our tank holds 180 litres.

We are thinking about moving from TrustPower to Electric Kiwi and using the hour of free electricity to heat water in the evening. I'm not sure if that makes sense yet, the unit price is better but there is no prompt payment discount and we would not get paid for exported power. I think it would be good in the winter when our own generation is low and we could go crazy with the dish washer, washing machine, dryer etc for an hour a day. I would really like to move to Flick, but they don't service our area.

Reducing the power bill is my new hobby ;)

KrazyKid:

Thanks for the replies

I am interested in turning off the cylinders for periods of time. Thus the temp is going to drop below 60 degrees.

I think I will save money by time-shifting the cost of the power to non-peak periods.

I also think (but have no evidence) it will be cheaper to only heat a cylinder 8-12 hours a day rather than maintain the temp at a constant level by heating all day.
My families usage is 2 showers in the morning and the kids baths/showers in the evening. I think that heating the water to temp for 4 hours on, 8 hours off could be cheaper
Having a modern well insulated cylinder should help with this second theory.

Does anyone have evidence that my 4 hours on - 8 hours off theory is correct?

tchart

1534 posts

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# 1672737 17-Nov-2016 12:46

timmmay:

You don't want to adjust the cylinder temperature, you want a mixing thingy (valve?) after the cylinder to mix in variable amounts of cold water. This ensures the bugs are killed but reduces the temperature at the tap. This was done by default for my new relocated cylinder a few years ago.

Hey @timmmay all our taps have mixer "thingys" (it a newish build ~6 months old). Problem is the water is so friggin hot its dangerous. We usually have to turn the mixer to 3/4 cold to get a decent temperature for the bath, dishes etc.

timmmay

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# 1672739 17-Nov-2016 12:48

One person supports this post

tchart:

Hey @timmmay all our taps have mixer "thingys" (it a newish build ~6 months old). Problem is the water is so friggin hot its dangerous. We usually have to turn the mixer to 3/4 cold to get a decent temperature for the bath, dishes etc.

Not at the taps, there's a knob right after the hot water cylinder, before it goes out to any taps. Our cylinder is in the ceiling, the knob is up there right by the hot water output. It mixes in some cold with the hot to reduce the temperature. I had the plumber set our hot water relatively cool, I watched him doing the setting - just turned it for a bit then tried it.

You may already have this if it's a modern install. Ask your plumber.

redmouse

69 posts

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# 1672740 17-Nov-2016 12:49

3 people support this post

I think the thingy is a tempering valve, installed near the cylinder.

tchart:

timmmay:

You don't want to adjust the cylinder temperature, you want a mixing thingy (valve?) after the cylinder to mix in variable amounts of cold water. This ensures the bugs are killed but reduces the temperature at the tap. This was done by default for my new relocated cylinder a few years ago.

Hey @timmmay all our taps have mixer "thingys" (it a newish build ~6 months old). Problem is the water is so friggin hot its dangerous. We usually have to turn the mixer to 3/4 cold to get a decent temperature for the bath, dishes etc.

KrazyKid

768 posts

Ultimate Geek

# 1672941 17-Nov-2016 16:34

redmouse:

We are thinking about moving from TrustPower to Electric Kiwi and using the hour of free electricity to heat water in the evening. I'm not sure if that makes sense yet, the unit price is better but there is no prompt payment discount and we would not get paid for exported power. I think it would be good in the winter when our own generation is low and we could go crazy with the dish washer, washing machine, dryer etc for an hour a day. I would really like to move to Flick, but they don't service our area.

@redmouse Interestingly I have just moved to Electric Kiwi and their hour of free power got me thinking about putting a timer in. We have flick here in Dunedin but with the fixed rates we pay here in Dunedin it seems to work out similar pricing overall. I'm going to give Electric Kiwi a year and then maybe trial Flick. Your lack of buyback will make it a more complicated choice for you.
If you have any questions about Electric Kiwi give me a yell, and if you need a $50 sign up credit let me know as well (I get $50 off my bill as well)

Like you I am finding new ways of saving power especially by timeshifting - up to the point of manually turning the hot water off & on :)

Rikkitic

Lock him up!
10679 posts

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# 1672948 17-Nov-2016 16:47

Ideally everyone should have a tempering valve but not everyone can have one. We live in an old farmhouse fed with spring water from a gravity tank. When the new cylinder was installed, the plumber had to get dispensation from council authorities to leave out the tempering valve, because our water pressure was too low and otherwise the hot water wouldn't have been able to reach the second floor. This isn't a problem with the cylinder because we rarely have the power on and when we do the thermostat keeps it from getting too hot. The problem is the wetback. Sometimes we actually hear the water boiling and then we have to open the taps to let the steam escape. Fortunately we are aware of the danger and no children use our showers.

I don't think there is ever a bad time to talk about how absurd war is, how old men make decisions and young people die. - George Clooney

tdgeek

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# 1673067 17-Nov-2016 18:45

I turn my solar hot water off now, apart from the odd need. Had a shower the other week it was 46.7, but it was fine. I noticed it but wasn't worth changing mixer. Often in summer its 80+ . Fir some reason, if I leave the mixer as it is, (hot and cold mix) and pull it out to add more water, it seems to add more cold than hot, so thats odd, but good. I don't care if the HW goes under 60, or well under as it will be brief. A few hours max.

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