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82 posts

Master Geek

# 251693 7-Jul-2019 09:15
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We are having a modest (165m2) single storey house built for my wife and I out Hobsonville way here in Auckland. We have specified a heat pump in the lounge. With double glazing and insulation we anticipate that this will be enough for most of our heating requirements.


My wife retires next year so there will be someone home most days.


The subdivision has piped gas. I am trying to work through our energy options and can't get any good stat's to guide me.


Any thoughts on what should guide my choice between gas and electricity for hot water?


Not sure about using gas for cooking...


Solar as a way of heating the hot water during the day looks promising, especially as Kiwibank offers a deal where they pay $2,000 towards any solar installation over $5,000.


$5,000 would cover a smallish install of solar and as I would only need to recover savings of $3,000 the pay back time / cost benefit may be positive.


What's the collective wisdom ?





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Uber Geek


  # 2271261 7-Jul-2019 10:11
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I wouldn't bother with gas at all, unless you want resilience from power cuts. I'd do ducted heat pumps, or maybe Central heating with radiators, which are silent but can't cool. Cooling bedrooms is a big win I think, so ducted heat pump is nice.

For cooking I like induction hob. Better than gas, easier to clean.

Solar, your call really. Payback period is major concern, but if you can use it during a power cut that's another win.


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Uber Geek


  # 2271264 7-Jul-2019 10:21
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Gas has a relatively high fixed charge, then a low per unit cost. The orthodox view is that gas only makes financial sense if you use it as much as possible - certainly heating and hot water, and potentially things like oven hobs and clothes dryers. It will be pretty expensive using reticulated gas just for hot water.

Gas has some lifestyle benefits. Faster heating and continuous hot water, and works effectively even in very cold climates. It is a fossil fuel, but is generally considered a transition fuel. Depending on your perspective, that may be a great or a terrible thing.

New gas exploration is on hold/cancelled, and so it will have some kind of end of life at some stage, though not sure when that will be.


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Uber Geek


  # 2271265 7-Jul-2019 10:23
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Gas should only be burned outside the house. I'd think electricity would be greener and more future proof, plus the daily charge.

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Uber Geek


  # 2271277 7-Jul-2019 11:03
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The boring old electric hot water cylinder is cheap to install and run, especially if you can get in on a controlled power rate often called economy. Its also the most reliable option with relatively cheap repairs if needed. If you're worried about running out of hot water, just get a bigger cylinder.

For a small household, you can expect a long payback on the big up front cost of heat pump or solar hot water.

Piped gas probably won't be worth it if you've got space heating covered by heat pumps. Bottled gas with an instant water heater might be similar in cost to electric cylinder, but clearly more negative environmentally - might as well take the environmentally friendly option if the cost is comparable IMHO

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Uber Geek


  # 2271282 7-Jul-2019 11:15
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I vote for solar HW. My cylinder is off 6 months a year. And in the cool season I use timers to manage the water I need, there is no need to fully heat the entire 300L all the time

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Uber Geek


  # 2271298 7-Jul-2019 13:23
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I vote for solar HW. My cylinder is off 6 months a year. And in the cool season I use timers to manage the water I need, there is no need to fully heat the entire 300L all the time



Not all the time, but at least weekly it should be at full temperature to kill legionnaires disease. I prefer to heat to full temperature each day - I do this during my free hour of power - though it usually takes a few hours since we use a lot of hot water.

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Ultimate Geek

  # 2271322 7-Jul-2019 14:59
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Regarding heating, I would recommend considering some means of low running cost heating for the entire house. Heat from a high wall heatpump in the lounge doesn't migrate particually well to other rooms (especially if you compare to a wood fire). I would look at some kind of central heating. Such as a ducted heat pump, hydronic underfloor heating (Either heated by gas of air to water heat pump, or radiators (gas only, unless you are willing to really oversize them.

I would also consider a balanced pressure ventilation system (proper heat recovery with a heat exchanger). Can be integrated into the ducted heat pump system if you go that way, or stand alone.

If their is opportunity to go above code for insulation, I would do it. Make sure your down lights (if any) don't vent your heated air into the roof space. (most modern LED unit's don't).

Regarding natural gas. Rough (marginal) cost of energy is... Natural gas: 8c/kWh, Standard user electric (16c/kwh), Low user electricity (26c/kwh). Piped gas has a monthly connection fee of about $36, a standard user electricity connection of $54, and a low user electricity connection of $10.

One of my past flats had natural gas for hot water, and stovetop only. We our savings from gas being cheaper than electricity roughly matched the connection fee.

As other have said, if you are going to have gas connected, to make the most of it, you want to use it for a lot of things in order to "pay back" the connection fee. i.e. hot water, stove top, tumble dryer. Can even have an outlet put in to connect your BBQ to (and have the injectors swapped to suit natural gas.

With regard's to hot water. Big advantage of gas is that the most popular units are tankless. These are way smaller, and are typically mounted on an outside wall, freeing space in your house. Their big advertising push is "never running out of hot water", but you should never run out with an appropriately sized electric cylinder either. An electric cylinder has the advantage of keeping your linen cupboard warm, and lasts a lot longer than a gas tankless heater. If you want to further-proof for solar, you can get a larger tank with dual element's This means you can leave the top element on it's thermostat, meaning you won't run out of hot water, and don't have legionella issues, while your bottom element can soak up the extra energy from our solar diverter. Could also /alternately do solar thermal with a coil in the tank, and evacuated tubes on the roof. If you get a cylinder, mains pressure ones are better than low pressure.


With regards to space heating. Even with the lower price of natural gas, heat pumps work out cheaper to run. That said, gas is a bit more flexible, it that it can heat to high temperatures with minimal extra losses. This means that it can run a radiator based central heating system, or if a fan forced system, it will blow a lesser amount of much hotter air, meaning the room feels less drafty. Also the performance doesn't drop with temperature (not that that is a big issue in Auckland where we rarely go below 5 dec C. Big advantage of a heat pump system (excluding underfloor) is that they can be run in air conditioning mode in summer, if required.

Current house doesn't have gas connected although I is available in the street. Personally I am pritty happy with this setup. Our heating is done with a heat pump and some portable resistance heaters. Cook-top is the induction type (these are awesome). Hot water is a standard mains pressure cylinder. We are well into standard user territory so we have a low per unit rate. Note that some lines companies give lower prices to those who have a electric hot water cylinder (controlled load).


If you are going for a tank style hot water heater, consider requesting "ring main" plumping. This is where you have a tiny pump that pumps hot water around a loop, so you don't have to run hot taps waiting for the hot water to arrive. Cost energy (need super good lagging on ringmain), but saves water. Very convenient.


Regarding gas for cooking, Gas is great for Wok's. For everything else, I am plenty happy with my induction cook-top. It's much faster at boiling water etc than the gas at my old flat. Downsides is that my induction cook-top needs a 32A electrical connection for itself, and that it costs about $1800 (a gas cooktop is about $400)


Personally I wouldn't do solar PV at the moment (generally payback period is very slow) but would specific conduit be run from the main switch board, to a garage wall / utility cupboard  (where inverter's could be mounted), and from their to a north facing area of roof. This mean's it if you decide to go for solar in the future, you install will be easy and tidy.

General electric future-proofing.


  • Insist on heaps of sockets (i.e. every wall of every office and bedroom), and 8+ at bench level in the kitchen.
  • If you can get it at reasonable cost, try and get three phase power installed (even if you don't require right now).
  • Get an oversize main switchboard so you can add stuff in the future.
  • Run conduit or cable to suit either 32A single phase, or 16A three phase, from the main switch board, to every car parking location (both garage, and outdoor spots. It is predicted that Electric cars will become a big thing in 10 - 20 years time, and this will be very helpful then.



Of course, the above will add cost to the build... up to you if it is worth it.


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Uber Geek


  # 2271361 7-Jul-2019 18:04
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I vote for solar HW. My cylinder is off 6 months a year. And in the cool season I use timers to manage the water I need, there is no need to fully heat the entire 300L all the time



Not all the time, but at least weekly it should be at full temperature to kill legionnaires disease. I prefer to heat to full temperature each day - I do this during my free hour of power - though it usually takes a few hours since we use a lot of hot water.



What matters is the top of the cylinder. Our 300L the top meter is at the top third i.e. top 100L the bottom is 2/3. As as the top that we use has been 62 Im happy. The borrom might be 62, then we use water so cold goes in, no need to pay to heat that. But I agree its essential to manage this. Some use more than others. 

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Uber Geek


  # 2271522 7-Jul-2019 22:27
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I would suggest not doing gas purely for the environmental factor. 
As @timmmay says above, induction hobs give you the speed benefit of cooking with gas, without the safety and environmental cost. 


Heat pumps are cheap to install, run and very efficient. The electricity grid in NZ is also very environmentally good. 


A cylinder with solar hot water would be a great option to reduce your power bill. 

Ray Taylor
Taylor Broadband (rural hawkes bay)

There is no place like localhost
For my general guide to extending your wireless network Click Here

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Uber Geek


  # 2271524 7-Jul-2019 22:39

Consider installing small heatpumps in each bedroom. That way you can keep just the bedrooms heated / cooled. Smaller capacity models actually have better efficiency than larger models. So it can be very worthwhile compared to using plug in heaters in the bedrooms. Still consider a ducted heatpump system though. Depends partly on whether you like keeping the whole house warm, or just heating only individual rooms.

Cooking - definitely gas running from a 9KG bottle, unless you are going to get induction cooking.

Hot water- Get a 300L cylinder. So if you get solar, you can store more energy. And less problems with running out of hot water. If you want gas hot water, connect to Natural gas. Dont bother with LPG hot water (since you have Natural gas available).

Windows - if Aluminum, get thermally broken frames. Also consider PVC frame windows.

EV charging. Run 32A to your garage/ parking area. If 3 phase, then 32A per phase. There are already EVs available that can charge at 3P,32A. Unless your switchboard is going to be in the garage anyway. Definitely get 3 phase power installed. You might need the 3 phase anyway if you get induction cooking.

Lots of Ethernet ports. Ceiling mounted Wifi access points. Small network equipment rack.

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Uber Geek


  # 2271571 8-Jul-2019 07:09
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Induction cooking doesn't require 3 phase, as far as I'm aware. We put a new induction hob in onto the same connection to the switchboard that was already there, though it needed a different plug.

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