Hot water accounts for roughly 30% of a typical NZ household's electricity use. On a standard plan that's just money you spend whether prices are high or low. On a spot plan, it's the biggest lever you have to reduce costs. The average NZ household spends $75–85 a month heating water. Shift most of that heating to periods when the wholesale price is cheap, and you can cut that bill by $30–55 a month.
The catch is that "cheap periods" aren't fixed. They shift with hydro storage, wind generation, and demand. You need something that watches the market in real time and acts on it. That's what Warden does — and this post explains exactly how the hardware and software behind it work.
The hardware
The PowerWarden device is wired into your hot water circuit by a licensed electrician, and then connected to your home Wi-Fi. When Warden says off, the element gets no power. When Warden says on, it runs normally.
The device has built-in energy metering — voltage, current, watts, and cumulative watt-hours. Warden records this every five minutes and shows it in your dashboard. You can see exactly how much energy your cylinder is using and when, which helps confirm the system is working.
How Warden controls the device
| Mode | How it works | Best for | Price |
|---|---|---|---|
| Schedule | You set fixed on/off hours. Warden executes them exactly, every day (or separate weekday/weekend patterns). | TOU plans, free-hour plans (e.g. Contact Free Nights 9pm–midnight), ripple-control replacement | $10/mo |
| Spot price | Warden watches the wholesale price at your node every 5 minutes and turns the element on when cheap, off when expensive. You set a "ready by" deadline as a safety net. | Spot plans (Flick, Electric Kiwi, Ecotricity ecoWholesale) | $20/mo |
Schedule mode is the simpler of the two. You pick which hours you want the cylinder running in the dashboard — and Warden pushes that schedule directly to the device. The device executes those jobs locally, independently of any cloud connection, which matters for the resilience story below.
Spot price mode hands control to the pricing engine. Warden reads the price at your specific grid node every five minutes. When the price is cheap the cylinder heats. When it's expensive, it stops. The deadline constraint — say, "ready by 6am" — is the safety net: if prices never dropped below your threshold overnight, Warden turns the element on before your deadline regardless. You always have hot water in the morning.
What happens when the internet goes down
This is the part most smart home devices handle poorly. If the cloud service goes down, or your home internet drops out, most connected devices just sit there doing nothing — which is fine until you run out of hot water at 7am.
Warden handles this differently. Every PowerWarden ships with a watchdog script pre-installed. The watchdog monitors the heartbeat signal that Warden publishes every minute. If it doesn't receive a heartbeat for 10 minutes, it stops waiting for instructions and activates an onboard fallback schedule — heating the cylinder between 1am and 5am local time, a window that's cheap on almost any plan.
The moment the cloud connection is restored, the first heartbeat it receives exits fallback mode immediately. Normal Warden control resumes without any intervention required.
This design philosophy — push intelligence to the edge — means the device is never fully dependent on any cloud service. It's a meaningful difference from smart plugs that become dumb bricks the moment their app has a bad day.
Provisioning: how a new device gets set up
On installation day, the electrician wires the device into the switchboard, connects to its Wi-Fi access point, and enters your home Wi-Fi password. Once the device joins the home network, the rest happens automatically. The whole process takes under 60 seconds from the point the device joins the home Wi-Fi.
Pricing
The economics work because Warden's subscription cost is a fraction of the savings. A typical NZ household saves $30–55 a month on hot water electricity alone. Schedule mode costs $10/month; spot price mode costs $20/month. At the conservative end, that's still a 2–3× return on the subscription.
Warden currently supports NZ households on spot plans and TOU plans. Sign up for a free 90-day trial — all features, no credit card required — and see your local price data live before you commit to anything.
What's coming
Hot water is the first load. This system works equally well for pool heat pumps, spa pools, and EV chargers. The spot price mode dispatcher is designed to handle multiple devices simultaneously, with per-device deadline constraints and independent scheduling.
Battery arbitrage is the next horizon. Warden is in discussion with BESS suppliers for access to their cloud platforms, which would allow direct charge/discharge control without any additional hardware at the customer site. When that is operational, the same price signal logic that turns your hot water element on during cheap periods will also be telling your battery when to charge and when to hold.
The infrastructure is already there. The pricing engine watches every node in the NZ grid — and all five NEM regions in Australia — every five minutes. The question is just which devices are worth controlling, and what the right control strategy looks like for each one.