Need to replace the hot water system advice needed.

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DeepBlueSky

547 posts

Ultimate Geek

#243040 24-Nov-2018 17:55

Hi guys,
Our low pressure hot water tank is on the way out slow leak around the element, I live in Christchurch and the tank was installed in the 90s so age and possibly the chlorine. Bottom line we are upgrading.

I need some advice on which way to jump we will install a mains pressure solution, the plumber who quoted suggested enameled tank over stainless as chlorine affects Stainless too he said and enameled tanks are cheaper and if anodes are used and replaced every few years they should both last, and can be heated via power generated from a solar panel if we install this in the future.

Now the other wrinkle we could install a direct heating solution using gas to heat the water not sure about power.

My concern with direct heating is gas going up in price in the future making it not economic.

Are there any comparisons that have been published between the costs to heat water with a tank v direct heating solution. Also longevity do tanks last longer.

What choice would you make, any help is very much appreciated.

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#2133526 24-Nov-2018 22:44

Can't comment on tank materials.

If you are considering solar, you want to get a big tank (300L?) With a mid (or top) element. This means the top element can ensure you always have hot water, while leaving thermal capacity in colder water underneath it to be heated by solar when available.

Two ways to do solar hot water. Either the conventional way with pipes and an evacuated tube thermal panel or with a bottom DC rated element fed directly from PV panels. Second way is becoming more popular. Either way needs some method to prevent your tank from boiling if left unused in hot summer. Piped water systems generally dump water so the makeup water cools the tank down (a big issue if you are on tank water), With PV panels you would need an electronic means of shutting the system down.

Some tanks have an AC bottom element so you can heat up the entire tank if you want to. (i.e. make use of "hour of power", or off peak power pricing), also could be used if you expect an exceptional need for hot water (i.e. heaps of guests / filling up hot water bed or spa pool etc.). Some grid tie solar system have the option to divert AC power to a lower hot water cylinder element (as self use is better financially than selling back to the gird).

I don't know what you mean by Direct heating. My google searching came up with apartment building solutions where hot water and space heating is done in a centralized system. I assume you mean a gas fired central heating system that does both space heating and hot water. Such system's are available, but given there is no piped gas in the south island, you would need to run it on LPG which is expensive. If the system is fan coils or under-floor heating it would be more economic to run it off a air to water heatpump. (although heat-pumps aren't suitable to run systems with radiators)

Tankless gas water heaters are popular here. "Never run out of hot water" is a key selling point. Also can be cheaper to (especially if the house already has a piped natural gas connection is allready paying rental on 2x45kg lpg bottles), although will not be cheaper if run of 9kg BBQ bottles or if you have very low usage, and sign up for monthly gas connection fee or bottle rental just for hot water. The tankless heaters don't last as long as hot water cylinders, but do free up a cupboard in your house. Also the tankless heaters won't fire up for very low flows, and struggle with pulsating flows (had a washing machine that controlled the temp of warm by pulsing hot water on and off). Also in Christchurch, you would be on LPG bottles, so it is another (admittedly easy) chore to phone for a bottle refill each time it gets low.

DeepBlueSky

547 posts

Ultimate Geek

#2133538 25-Nov-2018 01:17

Thanks Scott,

Your information is really useful.

So basically we have two options Tank or Continuous hot water, we don't have gas installed so will require installing and running the 2x45kg units if I jumped that way.

We have an old house the current tank is around 270L I'll see if we can fit a 300L, we also need to rewire the house but the power to the tank is 90's vintage.

Could I get a tank with a top heater provision and install at a later date, I'm thinking when I sort out the power I may get solar around the same time.

timmmay

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#2133653 25-Nov-2018 06:14

I'd probably go with what your plumber recommended, a mains pressure tank, whatever variation he suggests will work well in your area.

You could get Electric Kiwi for a free hour of power (using my referral link so both get $50 credit if you like), and put a timer on your hot water so it heats up then - though you'll probably need more heating at another time of the day if you're high demand. It cost me $250 to get a timer purchased and installed. If you do EK you want a tank with a decently powerful element to get more heating done in a short time - mine is 3KW but don't know if there's much option there. 3kw at 20c/kw = 60c saving per day = $220 savings per year just from hot water. In practice with heat pumps, clothes dryers, dish washers and such of timers I've saved $545 in the past year using hour of power, 20% of my power bill.

IMHO solar electric power is still too expensive, with very long payback periods, so I'd only do it if you had unreliable power or had another reason to do it.

nickb800

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#2133656 25-Nov-2018 07:35

If you can fit a 300l tank, then I'd go for that and put it on night plus tariff plan.
Heating times are controlled by Orion - generally 8 hours overnight and 4 hours in the afternoon. With a 300l tank, you should have enough storage to last in-between the heating times.

Looking at Genesis for example, rate would be 12c/kwh - probably cheaper than bottled gas, and better than investing in solar.

Will require a bit of electrical work - possibly rewiring between your electricity meter and switchboard, as often in Christchurch the hot water is ripple controlled but not separately metered.

timmmay

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#2133671 25-Nov-2018 08:38

nickb800: If you can fit a 300l tank, then I'd go for that and put it on night plus tariff plan.
Heating times are controlled by Orion - generally 8 hours overnight and 4 hours in the afternoon. With a 300l tank, you should have enough storage to last in-between the heating times.

Looking at Genesis for example, rate would be 12c/kwh - probably cheaper than bottled gas, and better than investing in solar.

Will require a bit of electrical work - possibly rewiring between your electricity meter and switchboard, as often in Christchurch the hot water is ripple controlled but not separately metered.

My observations are that a few hours a day of water heating is enough for a family of three, including daily baths.

Aredwood

3885 posts

Uber Geek

#2133712 25-Nov-2018 11:37

Definitely the twin element 300L cylinder, using night rate power. Get the bottom element connected to night rate power. And the top element on anytime power, controlled by a separate switch. So if you run out of hot water, you can reheat just the top of the cylinder quickly. without needing to wait for night rate power to start again.

LPG via the 45KG bottles costs around 17c per unit + daily charges. So a no brainer to get electric hot water on night rate power if you can get night rate power for 12c per unit.

JimmyH

2886 posts

Uber Geek

#2133757 25-Nov-2018 14:36

I am a fan of continuous flow gas hot water.

I found that that when I replaced my cylinder with a continuous flow unit my gas use basically halved, as I was only heating water when I needed it rather than keeping 300L of water at 65+ degrees 24/7 for two showers in the morning and a bit of laundry and washing up at night. That and getting the whole cupboard that the cylinder had taken up for storage, and never running out of hot water were also big pluses (I like long showers!).

You don't say what your family circumstances are, but if you have young children the continuous flow units are also safer. Mine goes up to 55 degrees, and 50 degrees is plenty hot enough for domestic use. Whereas cylinders have to be set north of 65 degrees to stop nasties (legionnaires etc) growing in the tank, and for a young child that's hot enough to scald. When I had friends with kids visiting I would just drop the temp to 45 degrees on the control panel, and was happy knowing they they couldn't run the taps or fill a bath with water that was hot enough to burn.

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rosco62

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#2133765 25-Nov-2018 15:02

JimmyH:
I am a fan of continuous flow gas hot water.

I found that that when I replaced my cylinder with a continuous flow unit my gas use basically halved, as I was only heating water when I needed it rather than keeping 300L of water at 65+ degrees 24/7 for two showers in the morning and a bit of laundry and washing up at night. That and getting the whole cupboard that the cylinder had taken up for storage, and never running out of hot water were also big pluses (I like long showers!).

You don't say what your family circumstances are, but if you have young children the continuous flow units are also safer. Mine goes up to 55 degrees, and 50 degrees is plenty hot enough for domestic use. Whereas cylinders have to be set north of 65 degrees to stop nasties (legionnaires etc) growing in the tank, and for a young child that's hot enough to scald. When I had friends with kids visiting I would just drop the temp to 45 degrees on the control panel, and was happy knowing they they couldn't run the taps or fill a bath with water that was hot enough to burn.

What that man above said re continuous flow h/water. My case, I had a 330 litre stainless cylinder and added an 18 tube solar system ( over 3 k worth ) family of 4, in winter made no savings as minimal heating from the sun. From December to February ( when you don't want hot showers ) the system was bonkers, water boiling hot, over rode my cold water tempering valve all the time, was always venting out the relief valve onto the roof.
Due to house renovations I replaced it with a continuous flow system, gas has been around the $ 93 per 45kg bottle since I had it installed , maybe 3 years and electricity is going up. My 10 cents worth.
I still have the solar system sitting around waiting for a new owner. Would work great as a straight thermo siphon system for a spa pool I reckon.

nickb800

2715 posts

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#2133778 25-Nov-2018 15:28

JimmyH:
You don't say what your family circumstances are, but if you have young children the continuous flow units are also safer. Mine goes up to 55 degrees, and 50 degrees is plenty hot enough for domestic use. Whereas cylinders have to be set north of 65 degrees to stop nasties (legionnaires etc) growing in the tank, and for a young child that's hot enough to scald. When I had friends with kids visiting I would just drop the temp to 45 degrees on the control panel, and was happy knowing they they couldn't run the taps or fill a bath with water that was hot enough to burn.

This is pretty much irrelevant for a modern cylinder, as they are required to be installed with a tempering valve which dilutes the 60+C hot water down to 55C (or lower if you ask your plumber when installing) before it goes to taps etc.

It's also worth mentioning that instant gas isn't everyone's cup of tea - the burst of cold water in between hot when you restart the hot tap drives me crazy when filling the bath or doing dishes. Can't wait to get rid of mine and replace with a cylinder

pctek

807 posts

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#2133844 25-Nov-2018 16:39

No it is NOT chlorine.

1.4million people in Auckland have had chlorine for ages without issues.

Acidic water eats out copper however.

But an '80s cylinder? It's had a good life. They don't last forever.

Replace it.

Scott3

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#2133883 25-Nov-2018 18:04

EECA puts energy losses from a modern conventional cylinder at $90 - $150 per year. It is common to get some value from that lost heat, if for example the cylinder is located in a linen cupboard (tiny bit of heat from the cylinder drops the relative humidity keeping linen dry and fresh).

Gas continuous systems are only 75% - 85% efficient as heat is lost through the exhaust (electric is 100% efficient at heating water, heat is only lost through storage)

Power is a bit cheaper in Christchurch than the north island, and no natural gas (street gas) is available, forcing you onto LPG.

If the 12c/kWh for power and 17c/kWh for bottled LPG numbers quoted are correct, financially it seems clean cut that electric is going to be the way to go. (especially when you consider the lower efficiency of gas hating, plus the cost of bottle rental).

Note that some houses will be able to go on a low user plan for electricity if they have gas hot water, reducing electricity daily cost, but increasing electricity cost per unit.

Also note that many power companies / lines companies will offer cheaper power if you have a hot water cylinder as they can shed this load is the network is stressed.

Electricity is way greener than Natural gas too (especially in the south island). (With the potential to add solar (either thermal or PV in the future with a correctly selected cylinder)

If you already had natural gas connected in the north island, I would strongly support you going gas.

There was an old thread on here about inverterless PV water heating:

https://www.geekzone.co.nz/forums.asp?forumid=141&topicid=230423

Sidestep

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#2133884 25-Nov-2018 18:05

nickb800:

It's also worth mentioning that instant gas isn't everyone's cup of tea - the burst of cold water in between hot when you restart the hot tap drives me crazy when filling the bath or doing dishes. Can't wait to get rid of mine and replace with a cylinder

We (in NZ) have - Paloma 24l - externally mounted instant LPG hot water units, one per shower + a kitchen or laundry. We've always been happy enough with them, and we've used 'stacked' ones for more capacity in a commercial situation.

That initial burst of cold water is a bit annoying though.

In Canada we've just installed a - Rinnai - 'hybrid' flued system, consisting of an instant hot water unit with a small attached hot water tank that acts as a hot water 'accumulator' The initial hot water feed's from the tank, as more hot is required the instant heater kicks in, when shut off the instant water heater brings the tank up to temperature then shuts down.

So far, in a home situation with teen kids and a couple of showers going it's worked well (and no bursts of cold water)
We'll be looking to see if we can find something similar when we return to NZ to upgrade our units there.

nickb800

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#2134072 26-Nov-2018 07:40

pctek:

No it is NOT chlorine.

1.4million people in Auckland have had chlorine for ages without issues.

Acidic water eats out copper however.

But an '80s cylinder? It's had a good life. They don't last forever.

Replace it.

I agree that chlorine alone doesn't destroy cylinders as evidenced by chlorinated water supplies in most towns/cities and hot water cylinders normally lasting decades. However, correlation between the introduction of chlorine to Christchurch's water and the huge spike in cylinder failures is too strong to ignore. Research from the University of Canterbury on this wasn't conclusive but suggests it's a combination of the chemical makeup of the untreated water, sediment accumulating in the cylinder, and the chlorine. Given that, it's well worth heeding the local plumbers advise to go with enameled lining instead of stainless steel.

Suckerpunch

124 posts

Master Geek

#2134076 26-Nov-2018 07:48

Give this tool a whirl... https://www.energywise.govt.nz/tools/water-heating/

Paul1977

5042 posts

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#2134428 26-Nov-2018 13:41

In Christchurch we replaced our low pressure cylinder with continuous gas, and don't regret it for a second.

However, we were replacing a 180L cylinder and didn't have the space for anything larger.

While you are getting plumbing done, I'd recommend looking at whole house water filtration system as well to deal with the chlorine (if you find that to be a problem for you). Our are is really bad with the chlorine, and the filtration system makes it taste like it used to, and our bathroom no longer spells like a swimming pool.

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