Is gas hot water cheaper per unit than a standard HWC?

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AklBen

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#323777 14-Jan-2026 09:52

We've moved into a new property, and it has reticulated gas. It provides gas to the stove and the califont for hot water.

As we all know, gas means at least $60 per month in daily charges regardless of usage, then you'll also have the electric daily charges for everything else, but the advantage remains that hot water is not always being heated unless when being used.

We will eventually move to a traditional HWC in order to get rid of gas completely - but I do wonder, aside from the daily charges, is continuous hot water heated by gas cheaper per unit than an electric HWC?

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#3452802 14-Jan-2026 10:49

We are on mains gas as well. The daily charge ruins any kind of efficiency at least for us in a two person household. Perhaps a higher user can chip in, but our plan is to get off mains in the future. Ideally tie it in with a solar plan but it's ways off at the moment.

I suspect modern hot water cylinders are very efficient in the grand scheme of things.

cddt

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#3452807 14-Jan-2026 11:20

A few years ago gas was much much cheaper than electricity per kWh but these days it's so close you would have to be using industrial quantities to break even once you consider line charges.

Scott3

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#3452810 14-Jan-2026 11:35

Provide your Power & Gas prices per kWh, and somebody will work it out for you.

Gas instant style water heater is around 85% efficient, no standing losses (assuming we ignore the tiny bit of electricity to run the control system)

Electric cylinder (non heat pump) is 100% efficient, but has standing losses. For a 150 L cylinder, MEPS requirements (from 2005) require losses be less than 2.53 kWh per day. Not unusual for modern cylinders to way outperform this.

Some example power prices (Parnell, Auckland address, rates from Mercury website):

Standard User Power: $0.26 / kWh + $3.36/day

Low User Power $ 0.33 / kWh + $1.725 / day

Natural Gas $0.17 / kWh + $2.0355 / day

LPG 0.305 / kWh + $0.5865/day ($186 / bottle, unsure if this is a terrible deal, or just what LPG costs now)

Lets ignore the daily charges, and just work out the cost to get 1 kWh of heat into the water (and standing losses at 1.5 kWh/day.

Standard user power: $0.26 / kWh heat + $0.39 / day standing losses

Low user power: $0.33 / kWh heat + $0.50 / day standing losses

Natural gas: $0.20 / kWh + 0 standing losses

LPG: $0.36 / kWh + 0 standing losses.

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

In summary, if you are locked into the daily charges (i.e. you have other gas appliances, so couldn't disconnect if you changed your hot water to electric), Natural Gas is still the cheapest option on the list to heat your hot water. But the gap has closed fast. In 2008, natural gas was around a third of the cost of standard user power. Now it is getting close to parity. Seems we have entered a death spiral for residential natural gas in NZ, I would predict rates are going to continue to increase, to essentially milk the declining number of "sticky" consumers connected for all they can.

LPG is now more expensive than even Standard user power to use to heat hot water. Daily fee from Mercury is more than the standing loss on an electric cylinder (and even if that is committed to for other gas use, break even point is less than 17 kWh of hot water per day).

If you are buying new appliances, I would strongly advise moving away from gas. But as an existing natural gas user, is is prudent to keep using gas for everything you currently have, until a point you are ready to convert all your gas appliances to electric, and disconnect. Natural gas is still cheaper than power, it is just that $2/ day fee will more than consume all savings from the cheaper unit price.

Scott3

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#3452812 14-Jan-2026 11:44

2005 MEPS table for hot water cylinders (via an AI tool as I don't have access to standards)

scuwp

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#3452861 14-Jan-2026 11:57

They will have to pry my instant gas hot water system out of my cold dead hands...

Lazy is such an ugly word, I prefer to call it selective participation

AklBen

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#3452864 14-Jan-2026 12:14

Yep...just had a good look at a few bills and did some back of envelope maths...

The consumption from the califont looks around 1.6x the kWhs to do the same job as an elec HWC, but the gas is around 16c cheaper per kWh. Therefore, for us it's around 80c cheaper per day just on HW. Issue is (as we all know) that the daily charge adds another $2.07 per day on top of the elec daily - so erodes the cost savings.

The good thing is that when looking ahead to winter and higher hot water consumption, the blowout is small, even another 8-9kwh would only add another $1.

I guess if you were a big hot water user (over 15kWh per day) then you'd end up beating elec (vs. standard non-TOU rates or anything special).

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lxsw20

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#3452877 14-Jan-2026 12:51

scuwp:

They will have to pry my instant gas hot water system out of my cold dead hands...

Why? What can it achieve that mains pressure electric can not?

mkissin

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#3452881 14-Jan-2026 13:29

lxsw20:

scuwp:

They will have to pry my instant gas hot water system out of my cold dead hands...

Why? What can it achieve that mains pressure electric can not?

I’d absolutely love to get rid of our mains gas, and will eventually. The main thing I will miss is the fancy bathroom controller I have.

i can set the water temperature down to the degree, and get it to run my kid a bath. I just tell it I’d like 60 litres of water at 42 degrees, turn the bath tap on and walk away. After a bit of time, the gas califont turns the hot water off and beeps to let me know. Glorious.

cddt

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#3452929 14-Jan-2026 13:58

mkissin:

I’d absolutely love to get rid of our mains gas, and will eventually. The main thing I will miss is the fancy bathroom controller I have.

i can set the water temperature down to the degree, and get it to run my kid a bath. I just tell it I’d like 60 litres of water at 42 degrees, turn the bath tap on and walk away. After a bit of time, the gas califont turns the hot water off and beeps to let me know. Glorious.

That's pretty clever. We don't have anything like that.

I would also love to get rid of mains gas, but the capital investment would be quite intensive, not just financial but also practical and organisational.

We would need a HWC (not sure where it would be installed), heat pumps, new hob which would need new wiring etc... it's quite a lot to coordinate at once with different suppliers, various tradies, and the electrician and doing it piecemeal makes me worried we'll miss something and end up having to change a whole lot of the wiring...

AklBen

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#3452931 14-Jan-2026 14:05

cddt:

I would also love to get rid of mains gas, but the capital investment would be quite intensive, not just financial but also practical and organisational.

We would need a HWC (not sure where it would be installed), heat pumps, new hob which would need new wiring etc... it's quite a lot to coordinate at once with different suppliers, various tradies, and the electrician and doing it piecemeal makes me worried we'll miss something and end up having to change a whole lot of the wiring...

We're in the same position. We will move to induction cooktop as we're doing up our kitchen but I see the gas hot water staying. It's just not worth the $4-5k to move to a HWC.

antoniosk

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#3452934 14-Jan-2026 14:25

AklBen:

We've moved into a new property, and it has reticulated gas. It provides gas to the stove and the califont for hot water.

As we all know, gas means at least $60 per month in daily charges regardless of usage, then you'll also have the electric daily charges for everything else, but the advantage remains that hot water is not always being heated unless when being used.

We will eventually move to a traditional HWC in order to get rid of gas completely - but I do wonder, aside from the daily charges, is continuous hot water heated by gas cheaper per unit than an electric HWC?

My brother is on continuous gas heated water, and it is frankly not great value. He lives alone and his last bill consumed 213Kwh. We use a Rinnai Hot Water on Demand and consumed about 500kWh over the same period for 3 people.

Overall, centrally provided power (gas/elec/pigeon/cowpat/whatever) is just going to continue going up in price. You'll realise more value moving off onto your own system like solar, sun based water heating and so on. I don't think we'll ever be able to go completely offered but you can go a long way towards self-driven and managed systems.

Sigh.

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AklBen

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#3452936 14-Jan-2026 14:32

antoniosk:

My brother is on continuous gas heated water, and it is frankly not great value. He lives alone and his last bill consumed 213Kwh. We use a Rinnai Hot Water on Demand and consumed about 500kWh over the same period for 3 people.

213kWh at 11c a kWh is $23.43 ex GST.

500kWh at 11c is $55 ex GST.

Both of those is still pretty cheap, in my mind, compared to what I'd expect the HW portion of the bill to be.

Even if your usage for a hot water cylinder on electricity was half of that at 27c a kWh then gas is still cheaper per unit.

scuwp

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#3452937 14-Jan-2026 14:39

lxsw20:

scuwp:

They will have to pry my instant gas hot water system out of my cold dead hands...

Why? What can it achieve that mains pressure electric can not?

Never runs out
Full mains pressure all the time
No cost if not being used (when we are away)
Cost to transition would take several years to recoup any savings (if any)
Takes up no space

Changing to a regular electric system would be a step backwards IMO. If we did change, it would be a to a heat pump unit. But, if reports are correct, they are quite noisy (I have seen 2 in action and can confirm), take up quite a lot of space outside, and lifespan is only 10 or so years. By the time any energy savings are realised, they will be lost again to a replacement. Just makes no economic or practical sense to change.

Gas hobs are also awesome to cook on.

Lazy is such an ugly word, I prefer to call it selective participation

Batman

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#3452938 14-Jan-2026 14:48

if you have 3 teens and they all shower for 1 hour at max water flow twice a day ....

mudguard

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#3452940 14-Jan-2026 14:56

scuwp:

Just makes no economic or practical sense to change.

Gas hobs are also awesome to cook on.

It still relies on the gas price remaining stable. A few in my street have already changed over.

Last time I looked we pay:

Electricity per kWh $0.2655 and line charge $1.50

Gas per kWh $0.1364 and line charge $1.47

NB the gas kWh gets converted from a volume measurement. I think it does say how the actual use as well

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