· By Daryn Leaity, who owns and runs Ecosmart
The best time to heat your hot water
Set your hot water timer for the small hours, about 2am to 5am, when wholesale power has usually been lowest and, on most lines networks I checked, so is the time-of-use lines rate. For a cylinder using about 8 kWh a day, on our wholesale plan and one of the three time-of-use lines prices below, heating then instead of 6pm to 9pm came to about $430 to $540 a year less on average over the three years to September 2026, and $400 to $500 in the year to September 2026 alone. Those figures are before GST and cover the wholesale price and lines rate only.
Why does heating after dinner cost more?
In a lot of homes, most of the hot water goes in the evening: home from work, dinner, dishes, showers. Without a timer, the cylinder starts reheating as soon as that hot water's used.
That puts one of the biggest loads in the house right in the evening peak. Everyone else is cooking and heating too, so wholesale prices are usually among the day's highest, and many lines companies charge their peak rate.
A cylinder is really a big insulated flask. The water stays hot for hours, so there's no rush to reheat it. With a timer it waits until the small hours, when hardly anyone else wants power, and there's still hot water for the morning shower.
With us, that timing shows up on your bill twice over: in the wholesale price, which we pass through for every half hour, and in your lines company's charges, which we pass through at cost. On a plan with one price at every hour, it doesn't. The lines part is usually the bigger of the two.
Lines companies with a 0c night rate
Your lines company owns the poles and wires to your street, and on a time-of-use lines price its per-unit rate changes through the day. Some drop it to 0c overnight. Here are three.
| Lines company | Peak rate | Overnight rate and hours |
|---|---|---|
| Unison Rotorua and Taupō. R-THU: residential, standard user, time of use | 13.6c 7-11am, 5-9pm weekdays | 0c 11pm-7am every day |
| Orion Christchurch and central Canterbury. RSU: residential, standard user, time of use | 14.19c 7-11am, 5-10pm weekdays | 0c 3-5am every day 0.66c 10pm-3am weekdays |
| Northpower Whangārei and Kaipara. DM7-TOU: residential, standard user, time of use | 14.91c 7-9:30am, 5:30-8pm weekdays | 0c 10pm-7am every day |
2026/27 lines prices, checked October 2026. Cents per kWh, excl. GST, including the national grid charge, standard-user prices. Orion's 0c window is shorter, but with the wholesale price added, 2am to 5am was still its lowest-priced three hours on average. Your own lines company and price may be different, so check yours.
What's a timer worth over a year?
Say your cylinder uses about 8 kWh a day. That's my assumption; a big family will use more and a couple less. Here's what heating it 2am to 5am instead of 6pm to 9pm comes to in a year.
| Lines company | 6-9pm vs 2-5am, year average (c/kWh) | Less a year (about) |
|---|---|---|
| Unison wholesale at Whakatu, Hawke's Bay | Lines 12.8c → 0c Wholesale 16.2c → 10.4c | $540 |
| Orion wholesale at Islington, Christchurch | Lines 11.2c → 0.5c Wholesale 16.7c → 12.6c | $430 |
| Northpower wholesale at Otahuhu, Auckland | Lines 9.1c → 0c Wholesale 17.4c → 10.9c | $450 |
8 kWh a day for a year, before GST. Lines rates averaged over every day of the year, weekends included. Wholesale averaged from 1 October 2023 to 30 September 2026 at the nearest of the five places I measured, by straight-line distance (Whakatu, Hawke's Bay for Rotorua and Taupō). In the year to September 2026 alone, with lower wholesale prices, it was about $500, $400 and $400. Leaves out network losses and the cost of fitting a timer. A cylinder without a timer doesn't do all its heating between 6pm and 9pm, so your own difference will usually be smaller.
Those figures cover the wholesale price and the per-unit lines rate only. The rest of the bill still applies: network losses, the lines company's daily charge, metering, levies, our fee and GST.
If your lines price is the same at every hour, only the wholesale part moves: a more modest $120 to $190 a year over the three years ($90 to $140 in the year to September 2026 alone). Not sure which you're on? It's in the lines charges on your bill, or ask us. A time-of-use lines price is where most of the difference is.
Before you change anything
- If your cylinder is on ripple control (your lines company can switch it off at busy times), your lines price may be lower because of it, so ask us whether a timer would change it before you fit one.
- A timer changes when the cylinder heats, not how hot, and stored hot water should still reach at least 60°C.
- Spot prices aren't capped and can spike at any hour with little or no warning, so a timer keeps you out of the usual evening peak but it does not guarantee a low price.
Setting it up
- Find your cylinder's timer, if it has one. If it doesn't, ask a licensed electrician to fit one.
- Set it to come on about 2am and go off about 5am. If that's not enough hot water, start at 1am.
- Check the lines charges on your bill, then ask us which lines price you're on and when its low hours run.
Can something pick the hours for me?
If you run Home Assistant, it can read the forecast from our price API and turn the cylinder on in each day's lowest-priced hours. The API is for Ecosmart electricity customers. It publishes prices; it does not switch anything itself, so you'd still need a relay on the cylinder's circuit, fitted by a licensed electrician. The Home Assistant page has ready-made sensors.
Hot water timer questions
What time should I set my hot water timer to?
About 2am to 5am. Over the three years to September 2026 that was the lowest-priced three hours for wholesale power in all five places I measured, and on most of the lines networks I checked it sits inside the low overnight rate of a time-of-use lines price.
Do any lines companies charge 0c overnight?
Some do on a time-of-use price. For 2026/27, Unison (Rotorua and Taupō) charges 0c a unit from 11pm to 7am and Northpower from 10pm to 7am on their residential standard-user prices, and Orion charges 0c from 3am to 5am, all excl. GST.
How much difference does a hot water timer make?
On our wholesale plan, for a cylinder using about 8 kWh a day, heating 2am to 5am rather than 6pm to 9pm came to roughly $430 to $540 a year less on average over the three years to September 2026 on those three lines prices ($400 to $500 in the year to September 2026 alone). On a one-rate lines price it was $120 to $190 a year over the three years ($90 to $140 in the year to September 2026 alone). Both are before GST, on the wholesale price and lines rate only, and spot prices can still spike at any hour with little or no warning.
How I worked this out
Wholesale: final half-hourly prices from the Electricity Authority's EMI wholesale datasets, 1 October 2023 to 30 September 2026, at the Otahuhu (Auckland), Whakatu (Hawke's Bay), Haywards (Wellington), Islington (Christchurch) and Invercargill grid exit points. In all five, 2am to 5am was the lowest-priced three hours of the day over the three years, and 1am to 5am the lowest-priced four hours in four of them (Invercargill: 1:30am to 5:30am). Season by season it was the lowest, or within half a cent a unit of it, except in autumn 2026 in Wellington, Christchurch and Invercargill and autumn 2025 in Invercargill, when the middle of the day came out lower. The level moves more from year to year than between these hours: the 2am to 5am average was 16.5c to 19.7c in the year to September 2024 and 3.6c to 4.1c in the year to September 2026. See also our spot prices by region.
Lines: the 2026/27 residential prices of the 22 lines networks we hold prices for, which is not every network in New Zealand, for the year from 1 April 2026, checked 19 October 2026. Per-unit rates before GST, with public holidays read as weekdays. On 20 of the 22, a time-of-use lines price charges less overnight than on a weekday evening. On 19 of those, all of 2am to 5am sits inside the lowest rate every day; on the other, Orion, the lowest rate runs from 3am to 5am. With each lines price added to each region's wholesale average, 2am to 5am was still the lowest-priced three hours on average on all 20. The other 2 have no time-of-use price that is lower overnight, but both price a controlled or night-only supply below their anytime rate. 17 time-of-use prices on 4 networks don't state their hours in a form I could read, so they're left out of these counts.
The examples are Unison's R-THU (its Rotorua and Taupō price), Orion's RSU and Northpower's DM7-TOU, as each company publishes them: the standard-user prices. The low-user versions of Unison's and Orion's also have a 0c rate, but Northpower's low-user overnight rate is 5.32c. Some of Vector's Auckland prices also show 0c overnight, but Vector bills the national grid to us separately and we add it as a flat rate per unit, so they're not in the table. The worked figures assume the cylinder draws evenly over its three hours every day of the year, with each lines rate averaged over the year (weekends at their weekend rates) and the three-year wholesale average at the nearest grid exit point.