Hot Water Cylinder Replacement Options

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OmniouS

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#283914 19-Mar-2021 13:59

Our 21 year old hot water cylinder has just started leaking out of the bottom. I had a z-wave flood sensor underneath it which alerted us to the leak as soon as it started so we're pretty happy with that purchase!

The current cylinder is a 180L VE model with 2kw element. I'm just wondering if it would be worth it to replace with a 3kw or dual element model instead of a like-for-like single element 2kw model? Unfortunately the installation area is very constrained and we won't be able to fit in a larger unit. It's going to be an absolute mission to remove and reinstall.

We normally have 2 people in the (4 bd) house but have up to 5 guests staying (rarely). Our family will grow at some point.

We haven't run out of water yet. There is an additional 45l cylinder installed in the kitchen which helps.

We were quoted around the $3k mark to replace which was higher than I was expecting but this was attributed to the surrounding valves and plumbing needing to be replaced and the super-constrained installation area.

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#2677230 19-Mar-2021 14:32

just get a 3kw unit, unless you are running the hot water continuously it should be able to keep up alright.

Dingbatt

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#2677232 19-Mar-2021 14:36

If there are going to be teenagers in the house at some stage in the future, then go with the higher capacity unit.

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lapimate

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#2677240 19-Mar-2021 14:50

Have you considered a Stainless Steel cylinder (rather than Cu, or steel-porcelain-lined)?

Scott3

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#2677241 19-Mar-2021 15:00

We have a 180L 3kW single element cylinder. Only times we have run out is when the switch got physically turned off by stuff in the storage cupboard, or we were using hot water in a quite unusual way (where running out wasn't a surprise). Should note that some are's are more aggressive with use of ripple control on cylinders than our area.

I think 3kW is a good element size, and while I would get a bigger cylinder if I could, given OP's situation, 180L should be fine.

Dual element setups don't really add value if you are just using grid power to run the cylinder, but are useful in the following situations:

Solar PV - Can have the bottom element (and thermostat) fed from a timer or solar controller to use power when solar is available. Top element can always be on to mean a smaller quantity of water is kept hot 24/7. Reduces the risk of running out of hot water, while keeping the bulk of the cylinder cold untill there is sun. Also provides protection from legionella bacteria (need to have the cylinder hot every so often to kill the bactera).
Solar thermal - As above, but turn the bottom element off during normal times
Solid fuel (wetback on wood burner) - As with solar PV, but turn off bottom element. Frankly if having daily fires, don't really need a dual element setup as the fire makes heaps of heat to get the cylinder hot.
Time of use power setup - have bottom element timed to use night power, and top element always on (reducing the risk of running out if a lot of water is used during the day).

So the big question is if you are likely to do any of those things during the lifetime of the cylinder.

With all the above setups, both elements can be be over-ridden to be on when you have a lot of guests. Still, despite having 2 x 2kW elements, I would guess that a single 3kW setup will have a faster reheat time, as the location of that top 2kW element means it can only be used when you nearly run out of hot water.

Generally duel element setups are on much larger cylinders (cura 300L), for something like a family of four, with a 180L you likely need to heat the entire cylinder all the time to avoid running out, so dual element might not be of much value if you have a family.

[edit] - might want to check electrical capacity. - my understanding is that 3kW is defacto standard for cira 180L cylinders. There is a chance that the initial specifier picked out a 2kW instead so that that cylinder and your under-bench cylinder can share a 20A circuit or something like that. Might need a wiring change to accommodate a 3kW cylinder.

Dynamic

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#2677297 19-Mar-2021 16:09

When my last HWC died, I wish I'd taken a bit more time to look at options. In hindsight, I should have moved to bottled gas rather than replacing like for like.

As @Scott3 mentioned... think about changes you may have considered like solar heating that you could not justify before, but with this work going on it makes the other change easier to justify.

If you will stay with electric, consider adding a timer to the HWC. It doesn't need to hold 65 degrees all day and night. Switch off at midnight (after it has heated the water once the evening showers have finished) and on again at 7am to top up once the morning showers have finished. Off at midday, and on again at 7pm, or something like that. I strongly suspect the timer will more than pay for itself within 2 years.

Consider ditching the second cylinder in the kitchen. Having two HWC's ticking on and off may not be worth it, as long as you don't mind waiting a few seconds for hot water in the kitchen. Or, replace it with small instant hot water system? If you keep the HWC, could it benefit from being wrapped?

**very** well done having the flood sensor alert you early.

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decibel

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#2677305 19-Mar-2021 16:24

Have you thought about ditching the cylinder altogether and getting an instant-on water heater?

Never run out of hot water; though the drawback is that when kids become teenagers, they quickly work out that showers can now be endless.

https://www.stiebel-eltron.co.nz/single-phase-electric-instant-hot-water-system

skewt

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#2677310 19-Mar-2021 16:29

For around $3k you can get a gas system installed

Recently been through this process and in the end I opted for gas, gets rid of the HWC and gives me more space in kitchen.

xcubed

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#2677319 19-Mar-2021 17:03

Just something to bear in mind, the gas hot water systems all require electricity for ignition and control, so you're dependent on both forms of fuel. There were a few cases with the earthquakes where we had no electricity, but plenty of gas, and still had no hot water from our gas hot water system.

Also, if you have two 45kg bottles it's a good idea to keep one of them closed as a reserve for when the first one runs out. There's been several mornings where the gas has run out at my place and both bottles were open, so it was a couple of days before the next hot shower.

Scott3

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#2677323 19-Mar-2021 17:49

Regarding the suggestions for adding a timer to save power, a Losses from a MEPS compliant 180L cylinder should be less than 1.7kWh per day. at 17c/kwh power, this works out to 28.9c/day or $8.67 per month. Adding a timer would only slightly decrease the average temperature a little, and would only save a small amount of the above numbers. My gut feeling is a timer could only be justified if on time of use power (cheaper night power), trying to utilize self generated solar etc.

Losses from the small cylinder will be much lower numbers than the above. Would need to be weighted up against the water and energy wasted when running the tap and waiting for the hot water to turn up. Plus decrease in convenience. Swapping the little cylinder to an instant unit would require new wiring. Personally I wouldn't consider unless that cylinder is also at the end of it's useful life.

Re the suggestion to go instant electric for the whole house, in general this doesn't work (reverentially) in NZ. Those units linked to need 30 - 40A each, and generally are only big enough to do one outlet at a time. My house has a 60A (I think) main feed, so two people showering at the same time, plus a few appliances running would see the pole fuse blow.

Re gas, Bottled gas costs more than my low user power, so little value in that for me. Street gas is a lot cheaper, but means picking up a $30+ a month connection fee. Also gas hot water heaters don't last as long as cylinders in general. Should note that NZ is talking about a phase out of residential gas new connections by 2025, and total phase out by 2050 - Still time to get in if one really want's it, but it is looking like a dying fuel at this stage.

Jase2985

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#2677333 19-Mar-2021 18:23

when looking at gas consider what the government has recently said about gas in NZ.

Mehrts

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#2677354 19-Mar-2021 19:29

xcubed:

Just something to bear in mind, the gas hot water systems all require electricity for ignition and control, so you're dependent on both forms of fuel.

A UPS could most likely handle this for emergency situations when the power goes off.

Between that and LPG bottles, you should be pretty self-sufficient if something bad was to wipe out electricity & gas mains.

Eva888

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#2677388 19-Mar-2021 20:37

We had a separate small under bench kitchen cylinder that I had removed when we got a new mains pressure tank for the house. The kitchen was then piped to the main tank. I regret that decision because it now takes one minute (timed it) to get hot water to the sink and that’s quite a bit of waiting and cold water wasted. I haven’t noticed any obvious changes in electricity usage with it’s removal.

Huntakillaz

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#2677470 19-Mar-2021 23:44

There are heatpump hot water cylinders available as well, supposedly more efficient last time I researched it few years back

OmniouS

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#2677471 19-Mar-2021 23:45

Thanks very much everyone for the feedback. Lots of excellent suggestions here to consider and ask the plumber about.

Due to the constrained install area and existing 500x500 (I think it was) drip tray, we wouldn't be able to fit in a Stainless Steel unit without reasonable renovations which we can't really do at the moment after recently painting the house. These units seem to be larger than their VE counterparts.

We have bottled gas available at the other side of the house (2 x 45kg) that just feeds into a gas fire at the moment. We could investigate utilising this for a gas water heater. The pipes would need to run a reasonable distance but I'll ask about it on Mon. We also have a gas feed on the street but note the comments about this being deprecated at some point.

The instant on electric heater sounds like a great option to replace the 45l cylinder when it dies - it's around 15 years old. Removing the small cylinder and plumbing the kitchen into the main one might be possible. It is quite nice having near instant hot water in the kitchen though which would probably change.

Good point regarding the wiring capacity for the cylinder. There is currently a single 16A circuit on the fuse board that's marked 'Water Cylinder'. Not sure if this is for both cylinders or just the main one. The switch to the cylinder is a modern PDL unit with a reasonable size cable coming out of it so hopefully that's promising. Thankfully it's reasonably close to the main fuse board so we could look to run a new cable if necessary. There is also a ripple control unit installed.

I also wouldn't mind some sort of IOT current monitoring device (clamp around the cables?) to add to our home dashboard and monitoring to alert on anomalies

rogercruse

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#2677553 20-Mar-2021 10:45

The plumber that replaced our original 180l cylinder for the 300l unit explained that there is little difference in the prices of hot water cylinders - that is, a cylinder that twice the capacity isn't twice the price!. He further explained that there is little value in the unwanted original unit.

If we had the space, then I would have opted to have both cylinders servicing our hot water needs.

Our new tank wasn't much wider and the additional capacity was accommodated by a increase in the cylinder length.

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