Need a new hot water heater, seeing some advice please, thanks!

Forums › Home Workshop DIY › Need a new hot water heater, seeing some advice please, thanks!

1 | 2

CokemonZ

1036 posts

Uber Geek

#3257657 9-Jul-2024 08:48

I am sure I have a post about this somewhere else.

I have a family of 6 with two HWC's, one used by the 4 kids, one used by my wife and I.

Fairly recently the one that services the kids failed and I had to do the maths about replacing it.

We decided not to go for the heatpump option as:

Required some new piping to be run externally - at an additional cost
Required new electrical to be run - at an additional cost
Lifespan while reasonable is likely to be way less than the 25 years of a standard unit
If I recall correctly I couldn't make it pay for itself, even with electricity costs doubled (or maybe tripled).

We ended up going for a stainless steel cylinder, that has the option of adding solar or a heatpump later on should we so decide. The cost difference without that option if I recall was approx $150 at the time - YMMV

What I did invest in is a time of use power plan, and a bluetooth smart switch to turn it off at peak times, mostly heat overnight and do a boost from between 4 - 5pm to make sure there is hot water for showers for the kids.

This based on some very simple maths paid itself off in less than a year.

Spyware

3723 posts

Uber Geek

Lifetime subscriber

#3257670 9-Jul-2024 10:03

Your kids aren't having 25 minute showers though, 25 mins @ 9 litres/min basically drains a 180 litre tank.

Spark Max Fibre using Mikrotik CCR1009-8G-1S-1S+, CRS125-24G-1S, Unifi UAP, U6-Pro, UAP-AC-M-Pro, Apple TV 4K (2022), Apple TV 4K (2017), iPad Air 1st gen, iPad Air 4th gen, iPhone 13, SkyNZ3151 (the white box). If it doesn't move then it's data cabled.

Goosey

2775 posts

Uber Geek

Subscriber

#3257761 9-Jul-2024 15:04

Spyware:

Mercury recommend cutting showers to 4 minutes, Pulse Energy recommend getting gym membership.

hmmm that gym membership would then come with free tinea?
I don’t know what’s worse…shower at the gym or shower at the local massage parlour…

Kickinbac

414 posts

Ultimate Geek

#3257770 9-Jul-2024 15:31

Goosey:

Spyware:

Mercury recommend cutting showers to 4 minutes, Pulse Energy recommend getting gym membership.

hmmm that gym membership would then come with free tinea?
I don’t know what’s worse…shower at the gym or shower at the local massage parlour…

I didn't know you could get a membership at the local massage parlour. Did Pulse recommend that too to get free/cheap showers? But then nothing is really free...

Jase2985

13411 posts

Uber Geek

ID Verified

Lifetime subscriber

#3257781 9-Jul-2024 16:09

Spyware:

Your kids aren't having 25 minute showers though, 25 mins @ 9 litres/min basically drains a 180 litre tank.

Who has their shower on full hot though? Given its mixing with cold water, it would likely last quite a bit longer than 25 minutes

Scott3

3923 posts

Uber Geek

Lifetime subscriber

#3257793 9-Jul-2024 16:39

For those running out of hot water, flow rate has a massive impact.

We have a 130L mains pressure cylinder and likes our long shower's. Previously had the below shower head (with a flow restrictor as our water pressure is very high). Only ran out of water a handful of times over a decade, and only when something abnormal happened (filling up paddling pool with hot water via a hose etc.).

www.mitre10.co.nz/shop/stream-shower-head-h-90mm-w-186mm-d-375mm-chrome/p/173627

Just had the bathrooms renovated, and the new shower heads (a slightly better shower, but massively more water) will run out the cylinder from two long back to back shower's. Trying to decide if we go back to a lower flow shower head, or just dial back shower times a little.

Jase2985:

Spyware:

Your kids aren't having 25 minute showers though, 25 mins @ 9 litres/min basically drains a 180 litre tank.

Who has their shower on full hot though? Given its mixing with cold water, it would likely last quite a bit longer than 25 minutes

Yeah, Hot water cylinders need to be set to a minimum of 60 C to kill Legionella bacteria.

Lets say a 37 degree shower & say 14 Deg incoming cold.

The shower will be exactly a 50:50 mix of hot and cold, so that 180L tank will last 40 minutes @ 9L/min.

Plus if the (3kW) cylinder is heating, it is recovering at ~52L/h, which nets another 10 minutes over a 50 minute shower.

Scott3

3923 posts

Uber Geek

Lifetime subscriber

#3257820 9-Jul-2024 17:17

Castlvaniafan:

I've got a low pressur hot water heater in my attic which has done a decent job but is past its life span and needs replacing. I live in Wellington and typical Welly style I don't have much space outside, I do have a small corner outside but have to weigh up if it's worth taking it up with a hot water heater.

As I slowly upgrade my systems in the house I'm going to lower carbon footprint and lower power options with intention to completely remove gas (stove is the last thing now).

I just had a basic question as I'm not really familiar with LP vs Mains. Reason I ask is, if I have free space in my attice and very limited space outside. I'm considering just sticking with LP. My existing taps can take mains pressure though, just inspected all them and they are ceramic inside.

What is the advantage of going from LP to Mains?

And then I have a question about heat pump hot water heaters. As I'm weighing up the benefits of having an external heat pump water heater versus the space it's going to take up

Anyone in Wellington have one outside? How's the performance in the cold weeks like last getting down to 4-6* overnight?

Thanks!!

Unless you have any specific reason not to (i.e. wetback), go mains pressure. It's just nicer to have, and the cost difference isn't massive. The advantage is simply that you get more push from your hot water. Stronger showers & faster fill rates if you want to fill a sink for dishes etc.

Low pressure vs mains pressure won't have an impact on if you can use your attic space. The tanks are roughly the same size / weight.

On heat pump hot water cylinders, there are two routes: Combined heat pump and cylinder that all needs to go outside.

Haier Monoblock Mains Pressure Heat Pump Hot Water Cylinder

A split unit where you can put the cylinder wherever you like, and a air conditioner style box that needs to go outside (but because of it's lighter weight & smaller size, could potentially be wall or roof mounted.

gallery carousel 3

Outdoor cylinders are popular for replacing an outdoor gas water heater, or for people who want to free up cupboard space.

One thing to be wary of in a retrofit is that there is a decent chance your current hot water piping is optimized for your current hot water cylinder location, and the plumber will just run a pipe from the old to the new location. if this distance is long, you will extend your wait for hot water to turn up at the taps (and resulting water & energy wastage).

----------------

Economics on heat pump hot water is a bit touch and go. 10 - 15 years would be a good lifespan for a heat pump (vs 25 years for a simple cylinder), and assuming standard user power plans, you need to use a heap of hot water to get them to pay back (I haven't run the numbers myself)

But if you want to heat your water with minimum power, they are currently the most popular option (solar thermal seems to be in decline for some reason)

----------------

Solar + heat pump hot water is the ultimate, but is quite rare.

The reason being, is that with solar PV, most people will be exporting power, and buy back rates are fairly low (12.5c/kWh for genesis as an example). Hence any power that can go into heating water is much cheaper what it would be for a non solar household.

Preferred setup for solar PV is a very large duel element cylinder.

180L Rheem Twin Element Mains Pressure Hot Water Cylinder
Example is a 180L cylinder, but bigger is better if it will fit 250 & 300L seem common. Not you likely will use more hot water with mains pressure.

Have the top element wired to 24/7 or lines company controlled power. And the top element will kick in and keep the top 45L (for the example, varies by brand) of water hot (if you get that close to running out).

The rest of the cylinder is heated by the bottom element which can be fed via a solar diverter (or a simple timer to align with solar generation times or power company off peak times). If you use less than 135L per day, likely all will be heated by solar.

kotuku4

482 posts

Ultimate Geek

ID Verified

Lifetime subscriber

#3257871 9-Jul-2024 19:51

It really depends what you can fit in. I stuck with LP after original cylinder leaked at 20+ years old. Went from 180 to 250 litre. Have Palidin solar diverter to standard 3kw element.

Small house all electric with 4.9kw solar (2013). Added ceiling insulation and retro fit double glazed. One heat pump heats whole house.

Had five of us in house, now three. I budget $100 a month, but skip a few when account balance too high.

Still runout of hot water if teenagers have half hour showers.

All heat pumps seem to crap out at less than 10 years. From electrician and heat pump installer nextdoor to work, and mine last year.

WWHB

28 posts

Geek

#3257883 9-Jul-2024 20:32

Hot Water Heat Pumps are the best option, the higher up front cost will be offset with the power savings

1 | 2