PowerWarden — Hot Water Control

Your cylinder heats
whenever it feels like it.
Change that.

Heating water is your biggest controllable load. PowerWarden shifts it to the cheapest hours — automatically, every day.

PowerWarden is a smart relay that mounts in your switchboard and hands control of your hot water cylinder to Warden — which knows exactly when electricity is cheapest and acts accordingly. Most households spend $70–80 a month heating water at whatever time the thermostat decides. PowerWarden changes that. Your shower stays hot. Your bill doesn't.

Order PowerWarden See how it works
Without PowerWarden
~$1,270/yr
typical annual hot water cost — thermostat heats whenever it wants
4-person household, standard electric cylinder
PowerWarden — TOU plan
Save ~$690/yr
shift all heating to off-peak tariff windows automatically
annual hot water cost drops to ~$580
PowerWarden — Spot plan
Save more than TOU
heat only during the cheapest wholesale windows, every single day
spot consistently beats fixed rates over a full year — exact savings depend on your lines company

The average New Zealand family of four spends around $1,270 a year on hot water with a standard electric cylinder — roughly a third of their total power bill. PowerWarden shifts heating to cheaper windows and keeps that money in your pocket.

Based on ~3,500 kWh/year hot water usage at the NZ median rate of 36c/kWh (Powerswitch/powerbill.co.nz, 2026). TOU figure uses a night rate of ~16.5c/kWh (Canstar NZ electricity plan comparison, 2025). Spot savings vary by lines company tariff structure; network charges differ significantly by region. Savings are estimates; actual results depend on your tariff and usage patterns.

How it works

01 — Install

Your electrician mounts it in 20 minutes.

PowerWarden is a DIN-rail relay that fits in a standard switchboard. Any registered electrician can install it — the hardware is the same as any other 25A contactor, just with a WiFi module attached. No special tools, no subfloor access required.

02 — Connect

Pair it to Warden from your dashboard.

Once on your network, PowerWarden appears in your Warden dashboard. Enter the device code, confirm your cylinder circuit, and set your minimum hot water guarantee. Setup takes about 3 minutes.

03 — Save

Warden handles the rest.

Warden knows your tariff structure or live wholesale price and decides when to heat. Cheap window? Heat now. Expensive period? Hold. An always-on fallback schedule means hot water is guaranteed even if the internet drops.

Intelligent load control

Heat water when electricity is cheap. Hold when it isn't.

Whether you're on a TOU tariff or a spot price plan, the principle is the same: your hot water cylinder holds heat for hours, so the timing of when it heats is almost entirely flexible. PowerWarden exploits that flexibility automatically.

On a TOU plan, Warden schedules all heating in off-peak windows and avoids the peak rate entirely. On a spot plan, it reads wholesale prices continuously and heats during the cheapest windows each day — pausing when prices climb. Your morning shower is none the wiser.

On a TOU plan, a 4-person household saves around $690/year on hot water — compared to an uncontrolled cylinder. On a spot plan, savings go further: wholesale prices are near-zero for hours every day, and over a full year spot customers consistently pay less than any fixed tariff. Exact savings depend on your lines company tariff structure.
  • Tariff-aware scheduling — heats in off-peak windows on TOU, cheapest wholesale windows on spot
  • Hot water guarantee — set a minimum daily run time; Warden ensures the cylinder heats for at least that long each day, even if prices stay high
  • Spike protection — on spot plans, pauses load when prices climb above your threshold
  • Always-on fallback — local time schedule runs if your internet or Warden is unreachable
  • Energy metering — see exactly how much your cylinder uses each day
  • Manual override — turn on from the dashboard any time, one tap on mobile
  • Holiday mode — set a date range; the device stays off until you're back
  • Usage history — 30-day chart of cylinder activity against electricity cost

Installation

Switchboard mount. Electrician install. Done in 20 minutes.

PowerWarden is rated for standard NZ hot water circuits — 25A single phase. It mounts on a standard DIN rail inside your existing switchboard, in series with your cylinder circuit. No subfloor crawl, no new wiring runs, no ceiling access required.

Any registered electrician can install it. The job is straightforward enough that most charge a single call-out fee. We can recommend electricians in Auckland, Wellington, and Christchurch if you need one.

Certification

PowerWarden is certified for installation in New Zealand and operates within the AS/NZS 3000 wiring rules for switchboard-mounted equipment on low-voltage circuits.

Rating
25A single phase
Mounting
DIN rail (35mm)
Connectivity
WiFi 2.4GHz (802.11 b/g/n)
Metering
Real-time energy monitoring (kWh)
Fallback
Local time-based schedule when offline
Install time
~20 minutes by a registered electrician
Compatibility
Standard NZ hot water cylinders, all voltages
Market support
NZ (AU coming)

Integrations

Works with Home Assistant, too.

Already running Home Assistant? The Warden HA integration exposes PowerWarden as a switch entity with an energy sensor. You can build your own automations on top of it, or just let Warden's cloud control run while HA monitors energy usage.

If you prefer to drive everything locally, PowerWarden also supports MQTT control — publish a retain message to the device topic and it follows local commands, with Warden cloud as the fallback when there's no local instruction.

Home Assistant integration

Available via HACS. Surfaces PowerWarden as a switch entity and energy sensor alongside any other Warden devices in your account.

  • HA switch entity — control PowerWarden from any HA dashboard or automation
  • Energy sensor — cylinder kWh reported as a standard HA energy entity
  • Local MQTT — drive directly from HA or Node-RED without Warden cloud
  • Graceful fallback — Warden cloud takes over when HA is unreachable
  • HACS install — one click, no config files

Pricing

What it costs

Hardware once. Subscription monthly.

PowerWarden is a one-time hardware purchase. The Warden subscription covers cloud control and device management — cancel any time, no lock-in.

On a TOU plan, the typical 4-person household saves around $690 a year on hot water — putting hardware payback at around 8 weeks. On a spot plan, savings go further still: over a full year, spot customers consistently pay less than any fixed or TOU rate. The subscription pays for itself in the first week either way.

Hardware
$100
+ GST, one-time. Includes PowerWarden unit and install guide.
  • PowerWarden relay unit
  • DIN rail mount clips
  • Installation guide
  • 2-year hardware warranty
Optimise plan
$14.90
+ GST per month. Required for device control features.
  • Automated hot water control
  • TOU and spot plan support
  • Energy usage history
  • Home Assistant integration
  • No lock-in — cancel your subscription any time; the device continues on its local fallback schedule
  • Pay-on-dispatch — hardware charged when your unit ships, not at order
  • NZ shipping included — free courier to anywhere in New Zealand
  • 2-year warranty — replacement unit if anything fails
TOU payback: ~8 weeks for a 4-person household based on $690/year savings. Spot payback is faster — how much faster depends on your lines company, but over a full year spot consistently beats TOU on total cost.

Common questions

Does it work on a TOU plan or do I need to switch to spot?
PowerWarden works on both. On a TOU plan, Warden schedules all heating in your off-peak windows and avoids peak rates entirely — straightforward and effective. On a spot plan, Warden responds to live wholesale prices and can squeeze further savings by heating only during the cheapest windows each day. Spot delivers the biggest savings, but TOU alone is still a significant improvement over an uncontrolled cylinder.
Will I run out of hot water?
No. Warden turns the cylinder on when electricity is cheap — off-peak periods on a TOU plan, below your price threshold on a spot plan — and off when it isn't. You also set a minimum daily run time in your dashboard. If cheap periods haven't added up to that minimum by end of day, Warden tops it up regardless of price. The guarantee always wins over cost optimisation.
What happens if my internet goes down?
PowerWarden runs a local fallback schedule stored on the device itself. If Warden cloud is unreachable, the device follows a time-based heating schedule you configure at setup. Your cylinder keeps heating — just on a fixed schedule rather than a price-responsive one.
How long does installation take?
About 20 minutes for a registered electrician. The unit mounts on a DIN rail inside your existing switchboard in series with your cylinder circuit — no new cable runs, no subfloor access. Most electricians treat it as a standard call-out job. A detailed installation guide is included with every unit.
Does it work with a heat pump hot water system?
It depends on your model. PowerWarden controls the power supply to the unit, which works with most heat pump hot water systems. If yours has a dedicated compressor circuit or a smart control panel, get in touch before ordering and we'll confirm compatibility.
Can I control it manually?
Yes. There's a manual override in the Warden dashboard and mobile app — a single tap turns the cylinder on or forces it off, regardless of the current schedule. The override lasts until the next scheduled decision point, then returns to automated control.

Ready to stop heating water at random?

Order PowerWarden and have it installed in a day. Works on your current TOU plan — and saves even more if you move to spot.

Order PowerWarden See all plans →