Water & Heating conundrums in Kaiapoi

Forums › Home Workshop DIY › Water & Heating conundrums in Kaiapoi - advice appreciated.

steevg

90 posts

Master Geek

#311966 2-Mar-2024 15:34

Hi Geeks

My wife & I are downsizing & in the middle of a house buying scenario somewhere around Christchurch/Kaiapoi (may be a factor in your replies?).

We’re early retirees, no mortgage to worry about but on a fixed income. We're trying to calculate monthly running costs for Water, Power & Heating/Air conditioning & the possibilities of upgrading or changing existing systems & we’d like some advice if possible please.

The consideration for how long it may take us to recoup any (potential) initial outlay may not be a factor as we’re hoping to include this (or part of it) in any offers we make on a property.

Ripping out existing systems to replace them with more economical options is definitely something we’re happy to contemplate.

So we are considering the following:

Monthly cost of running an external infinity LPG water heater/annual equipment rent.
Heat-pump hot water system.
Solar Water system.
Heat-Pump “Central Heating” system (water & heating)
. . . any other options we haven’t considered yet, to keep monthly heating/water heating costs as low as possible?

Factors:

220sq mtr property (inc internal double garage)
2 Adults
1 Shower per day each
Dishwasher (every 2nd day)
Washing machine (2 loads per week)
Double width Fridge Freezer
Small Chest Freezer
Conventional Dryer (not Heat Pump type)
Working from home (regular cups of tea, possible heating during the day in winter etc.)

Any help/advice/calculations with this would be greatly appreciated.

SATTV

1648 posts

Uber Geek

ID Verified

#3202438 2-Mar-2024 15:51

I would not bother with a solar water system, I would go PV and use that to heat the water and any surplus can be used in the house or sold back to the grid.

I believe you have to get consent for solar water heating but you dont need one for PV

If you do go for solar hot water, get a very large take, a friend of mine has 400l stainless steel tank heated by 52 tubes, in the summer he covers half of them up and it can still get too hot, in winter it can get to 65 deg most days, he only had to use the element a couple of times over the years, he has the element turned off but it's controller will turn it on to heat the water if it falls below 65 deg for 1 week.

Solar water is great but PV is more versatile ( I have had both over the years )

John

I know enough to be dangerous

tweake

2391 posts

Uber Geek

#3202557 2-Mar-2024 21:25

for two people i would not bother with heat pump hot water.

external water heaters you have to watch for the pipes freezing in winter. internal is recommended.

single biggest thing is the houses insulation including air tightness. sad to say none of them will be good, its going to be what work is needed. then its what sort of home heating do you want or can fit. don't forget aircon for summer.

as above i would go pv over any water based system.

WWHB

35 posts

Geek

#3202581 3-Mar-2024 08:29

I wouldn’t go with solar water system either, you would get more benefit from pv

I am a big fan of Hot Water Heat Pumps, the issue you will have is with only 2 people the payback period on the higher up front costs will take a long time.

LPG is getting expensive, long term I can see people removing LPG continuous flow systems like the Rinnai Infinty and replacing with either a outdoor cylinder or hot water heat pump.

For a disclaimer I am a plumber/Gasfitter and gas hot water upgrades are getting less common with most clients getting outdoor cylinders or hot water heat pumps. If it wasn’t for how expensive they are pretty sure everyone would have taken a hot water heat pump.

eonsim

398 posts

Ultimate Geek

Trusted

#3202777 3-Mar-2024 17:01

Like the others I'd suggest getting a Photovoltaic (solar power) power system installed if you can afford it and your house roof is either east/north/west facing. Then get either a large electrical hotwater cylinder or a heatpump hotwater cylinder. Make sure the house has decent heat pumps for heating and cooling as the season requires.

A basic solar system (4-5kW @ $10k) will generate over 5,000kWh's a year (>30per day in summer, >8 per day winter). That should be enough to cover a decent proportion of you average daily power use and effectively allow you to run your hotwater and daytime heating/cooling for near free most days of the year. Short of stormy days where electricity generation is massively reduced you will likely use minimal or zero power from the grid during the day. If your electricity use is low enough a decent sized solar system (plus house battery, which I wouldn't generally recommend) can effectively wipe out your entire energy bill from reduced power use and credit from exporting excess solar.

You can have a look at the following solar calculator for better estimates.

https://genless.govt.nz/for-everyone/at-home/explore-solar-energy/solar-power-calculator/

If you go such route a number of banks offer green energy loans at either 0-2% interest for installing solar and other energy improvement. The system will likely pay for it's self in 8-10 years in energy savings (quicker if inflation stays high). Or there is solarZero who will install the system plus a battery in exchange for locking you into a 20 year power contract with them with a fixed electricity price for the entire time.

A solar power system is one of the best ways to reduce the impact of daily costs on your fixed income, assuming you have the capital for it, or are willing to sign up to SolarZero in exchange for a long term commitment. Especially as PHEV's and full EV's become more common over time and demand for electricity increases.

Scott3

3963 posts

Uber Geek

Lifetime subscriber

#3202827 3-Mar-2024 17:33

Your hot water needs sound modest, so it is unlikely that you have a reasonable payback period ripping out one system and replacing with another.

On LPG tankless: A quick google search has kiwi gas doing bottle rental for $50/year each (so $100/year total), and "from $139" per bottle swap fee (assume they charge extra for rural). A 45kg Bottle holds 625 kWh, so you are looking at 22c/kWh for gas, if burnt in a 90% efficient tankless water heater, that works out to 25c/kWh. More expensive than standard user power rates, but not cripplingly so. (and not storing the heat means about $100 of waste heat leaking out of your hot water cylinder is saved per year).

Heat pump. Save 1/2 to 1/3rd of the cost of power vs a normal cyclinder, but cost at least $2000 + install. If you used say 3000kWh of energy in a normal cylinder each year, at a power rate of 18c/kWh, and saved half of this, then you would be saving $270/year. lets say you were throwing away a perfectly good setup and the install + heat pump cylinder cost $2700, then you are looking at a decade long payback time. Midea brand one is what the pricing is based on and the warranty is 1-5 years depending on component. There is a risk the cylinder could die before it is played back (or it could run for 20 years)

Solar thermal (evacuated tubes etc.) is going out of fashion in NZ at the moment. You can still get them, but in general people who want to heat their water via solar do it via PV panels these day's. In short either have a timer or solar diverter, that runs your electric hot water cylinder when the sun is shining. If you are buying a new cylinder get one with non simulations duel elements, with the bottom getting fed by the timer or diverter, and the top one always on to make sure you don't run out of hot water if you use heaps one day.

Combined heat pump hot water & central heating. Kind of hard to retrofit. Heat pump sourced hydronic systems work best with underfloor heating (which requires a very major renovation to install), rather than radiators. of course Underfloor heating is very luxours, but I suspect people worrying about running costs will not tollrate the cost of it being retrofitted to an existing house.

Suspect sticking with current systems until their end of life is going to be the most cost effective.

If you do upgrade, I would go for a large (around 300L duel element hot water cylinder), and a rooftop PV system with either a timer or solar diverter feeding the bottom element of the cylinder.

Space heating (and cooling) should be taken care of via Mini split (i.e. high wall) or Ducted Heat pump(s).

steevg

90 posts

Master Geek

#3202831 3-Mar-2024 17:48

Thanks so much to everyone who has (so far) contributed. Very much appreciate the time you've taken to respond. This information has been very helpful indeed.

Will take some time to digest the info but looking towards the PV/Heat Pump options for lowest monthly costs.

Will keep checking back daily so please feel free to keep adding to this thread in the meantime.

Wheelbarrow01

1723 posts

Uber Geek

Trusted

Chorus

#3202910 3-Mar-2024 21:49

Scott3:

A 45kg Bottle holds 625 kWh, so you are looking at 22c/kWh for gas, if burnt in a 90% efficient tankless water heater, that works out to 25c/kWh. More expensive than standard user power rates, but not cripplingly so.

I'm not saying you're wrong but isn't this logic somewhat flawed? The instant gas water system is only heating while you are actually in the shower or running the hot tap. The moment you turn the tap off, it stops using energy. However if you have an electric cylinder and you shower for 15 minutes, the tank won't heat for just 15 minutes - it might heat for 30 or even 45 minutes.

I'm not advocating one way or the other - we have Rinnai instant gas at our bach because it makes sense - we have hot water available the moment we get there and we pay nothing for hot water when we aren't. We have power with the same company (Frank) so we don't pay for gas bottle rental.

However at home we have an electric cylinder and it works for us. I've thought about PV solar but it doesn't stack up for us. All our heating is provided by our ULEB log burner, for which we have a free source of fuel (and a cheap back-up supplier) - we spent just $200 to heat the house last year. Yes it involves some labour, but that warms me up three times - once to split it, once to load it onto the trailer, and once to stack it in the wood shed!

I am interested in evacuated tube solar for the hot water but have never looked into pricing. We're in Christchurch and our pitched roof faces directly north with no obstructions and there's only two of us in the house so perhaps it would be ideal to reduce our reliance on electricity even further.

Equinox IT

Cloud spending continues to surge globally, but most organisations haven’t made the changes necessary to maximise the value and cost-efficiency benefits of their cloud investments. Download the whitepaper From Overspend to Advantage now.

steevg

90 posts

Master Geek

#3203123 4-Mar-2024 16:49

Wheelbarrow01:

Scott3:

A 45kg Bottle holds 625 kWh, so you are looking at 22c/kWh for gas, if burnt in a 90% efficient tankless water heater, that works out to 25c/kWh. More expensive than standard user power rates, but not cripplingly so.

I'm not saying you're wrong but isn't this logic somewhat flawed? The instant gas water system is only heating while you are actually in the shower or running the hot tap. The moment you turn the tap off, it stops using energy. However if you have an electric cylinder and you shower for 15 minutes, the tank won't heat for just 15 minutes - it might heat for 30 or even 45 minutes.

I'm not advocating one way or the other - we have Rinnai instant gas at our bach because it makes sense - we have hot water available the moment we get there and we pay nothing for hot water when we aren't. We have power with the same company (Frank) so we don't pay for gas bottle rental.

However at home we have an electric cylinder and it works for us. I've thought about PV solar but it doesn't stack up for us. All our heating is provided by our ULEB log burner, for which we have a free source of fuel (and a cheap back-up supplier) - we spent just $200 to heat the house last year. Yes it involves some labour, but that warms me up three times - once to split it, once to load it onto the trailer, and once to stack it in the wood shed!

I am interested in evacuated tube solar for the hot water but have never looked into pricing. We're in Christchurch and our pitched roof faces directly north with no obstructions and there's only two of us in the house so perhaps it would be ideal to reduce our reliance on electricity even further.

. . . . from the comments I've had to date from a variety of different sources, the "Solar Heaters" appear to be being phased out due to long-term reliability issues in favour of the heat pump units.

Possibly others may be able to confirm/deny?

Scott3

3963 posts

Uber Geek

Lifetime subscriber

#3203201 4-Mar-2024 22:18

Wheelbarrow01:

Scott3:

A 45kg Bottle holds 625 kWh, so you are looking at 22c/kWh for gas, if burnt in a 90% efficient tankless water heater, that works out to 25c/kWh. More expensive than standard user power rates, but not cripplingly so.

I'm not saying you're wrong but isn't this logic somewhat flawed? The instant gas water system is only heating while you are actually in the shower or running the hot tap. The moment you turn the tap off, it stops using energy. However if you have an electric cylinder and you shower for 15 minutes, the tank won't heat for just 15 minutes - it might heat for 30 or even 45 minutes.

....

You missed quoting the last sentence of my paragraph:

"(and not storing the heat means about $100 of waste heat leaking out of your hot water cylinder is saved per year)."

In short, using energy for a shorter time in this case doesn't make you better off, as you are using the energy at about five times the rate.

The specific heat of of water is 4.18 kj/kg/degree

Means that heating 100L of water by 20 degrees is going to take 2.3kWh of energy regardless of time. If you are going to do it without storage, you need ~17kW worth of power for 8 minutes at a 12L/s flow rate. Trivial to supply by gas, but getting a bit much for most residential wiring, hence why electric storage tanks are used. An 3.6 kW storage tank is going to take about 38minutes (from the start of the shower) to recover to full heat, but in both cases the energy usage is the same 2.3kWh

Only things to consider are:

Relative energy prices (LPG tends to be a little more expensive per kWh than standard user power)
Relative efficiency. A gas instant heater is around 90%, an electric cylinder is 100%
Standing heat losses. A gas instant heater has none, and a MEPS compliant 135L hot water cylinder is less than 1.4kWh (less than 2kWh for a 300L).

On standing losses, a 300L cylinder loosing 2kWh a day 365 days a year, on 17c/kWh power would cost $124.1/year in standing losses. Roughly balances out with the cost of LPG bottle rental (unless you have to pay this regardless for something else).

Gas can work well in cases where Hot water is rarely used (but you want it immediately available if needed), as you save that $124 standing costs. Some batches use BBQ bottles as their supply, which means a higher kWh rate again, but no bottle rental fees.

Gas can also work where people are on low user power plans with expensive 30+ c/kWh rates. But low user plans are being phased out, and this perverse incentive is one of the reasons that is a good thing.

And of course instant water heaters are great for a use case where you need comical amounts of hot water. Want to fill one of those warehouse swimming pools with hot water... No issue.

As an interesting side note, I specified an electric instant hot water heater for an unmanned industrial facility I was designing. Very unusual in NZ, but I felt it was a nice pick. facility was unmanned so it would only be used when workers were on site for repairs etc, so avoiding the standing losses was desirable. And because the site needed a 750kVA transformer , the 20kW for an instant electric hot water heater was trivial.

https://www.stiebel-eltron.co.nz/dhe-au-instantaneous-3-phase-water-heater

Goosey

2829 posts

Uber Geek

Subscriber

#3203210 5-Mar-2024 06:23

Tounge in cheek…

I thought downsizing would be going to somthing less than 160m2 !
220 is an average 4bed family home !

WWHB

35 posts

Geek

#3203219 5-Mar-2024 07:37

The Midea Hot Water Heat pump from Trade Depot, I wouldn’t go there. Trade depot supply some of the lowest quality products I have ever installed.
When it comes to Hot Water Heat pumps you get what you pay for, there has to be a reason why they are so much cheaper than others (including Ecospring which is the exact same system with different branding on it).
If you want a quality system look at Rheem, Reclaim and Apricus models and for a good mid range look at Enviroheat and Stiebel Eltron units.

tweake

2391 posts

Uber Geek

#3203434 5-Mar-2024 17:23

Goosey:

Tounge in cheek…

I thought downsizing would be going to somthing less than 160m2 !
220 is an average 4bed family home !

but that includes the garage as well. it may have 180m2 garage 😋

Wheelbarrow01

1723 posts

Uber Geek

Trusted

Chorus

#3203541 6-Mar-2024 00:27

tweake:

Goosey:

Tounge in cheek…

I thought downsizing would be going to somthing less than 160m2 !
220 is an average 4bed family home !

but that includes the garage as well. it may have 180m2 garage 😋

LOL I think if I hadn't married, I'd be living in a carefully designed 180m2 garage with an internal access 40m2 flat by now 😂

Crazy cat lady? She's got nothing on the crazy car/boat/caravan/quadbike/golf cart guy 😂

steevg

90 posts

Master Geek

#3203807 6-Mar-2024 15:47

Goosey:

Tounge in cheek…

I thought downsizing would be going to somthing less than 160m2 !
220 is an average 4bed family home !

. . . . yup well spotted. Goosey !

The idea of downsizing was definitely on the cards, but then we saw this place advertised. Lovely property, great location (so we thought until we checked out the insurance premium this morning), very good possibility for a good price . . . and generally speaking, it ticked all the boxes for our retirement despite being a little large overall. The selling point for the wife, was that they'd just spent almost $50k on a new kitchen, then just about 2 weeks later, the guy had a stroke and needs to go into a retirement home.

The house needs the water, heating and air conditioning sorted out as it's all pretty old stuff in there . . . hence the post.

All great information as we now consider other properties.

(By the way, the double garage is pretty standard - 45-ish, sq metres, so the floor area is around 175).

sugarpie

56 posts

Master Geek

#3215374 7-Apr-2024 22:19

My partner and I went through something similar recently, really weighing our options between solar water systems and heat pumps. We found that while solar has an upfront cost, the long-term savings are significant, especially if you're planning to stay put for a while. Heat pumps, both for water and central heating, are incredibly efficient and can significantly cut down on monthly bills, even in a house your size. We did consult a Plumber in Sydney during our decision-making process. They were able to give us some great insights into what system would be more cost-effective based on our usage patterns.