A home energy monitor in NZ can be as simple as the half-hourly smart-meter data your power company already holds, or as detailed as CT clamps in the switchboard feeding a live Home Assistant dashboard. This guide explains each option, what it shows you and which ones need a licensed electrician, for households and tinkerers who want to know where the power bill actually goes.
It is worth the effort. MBIE’s August 2026 price survey puts the all-in national average at 42.1c/kWh, so its model household using 8,000 kWh a year pays around NZ$3,370, and trimming 10% is worth more than NZ$300 a year. Start with the running-cost calculator below. If you already run a Home Assistant box such as the Home Assistant Green, you are most of the way to a live energy dashboard.
Key takeaways
- Your smart meter already records half-hourly use. You can ask your retailer for up to two years of it, and they have five business days to supply it.
- Energy-monitoring smart plugs are the easiest way to measure individual plug-in appliances.
- Whole-house, real-time monitoring uses CT clamps inside the switchboard, and in NZ that is a job for a licensed electrician.
- Space heating and hot water were 63% of household energy in BRANZ’s HEEP study, so they are where savings usually hide.
- Home Assistant’s Energy dashboard can pull it all together locally, with no subscription.
Appliance running-cost calculator
Tick the appliances in your home, adjust the watts and hours to suit, and see what they cost to run per day, month and year at your power price.
| Use | Appliance | Watts | Hours a day | NZ$ a year |
|---|
Watts and hours are typical starting estimates, not measurements: check the rating plate, or measure with an energy-monitoring plug. Heat pumps, fridges and hot water cylinders cycle on and off, so use their average draw. Running costs exclude daily fixed charges. MBIE’s August 2026 survey put the all-in national average at 42.1c/kWh once fixed charges are included; the per-unit rate printed on a bill is lower than that all-in figure, so the calculator starts at 35c. Change it to match your bill.
In this guide
- How much power does my house use?
- Four ways to monitor home energy use
- Smart meter data in NZ: get your half-hourly usage
- CT clamp energy monitors explained
- NZ safety rules: who can install an energy monitor?
- Home Assistant energy dashboard setup
- Electricity usage by appliance: finding the energy hogs
- Common mistakes with home energy monitors
How much power does my house use?
MBIE models a typical household at 22 kWh a day, or 8,000 kWh a year, for its quarterly price survey. The most detailed NZ measurement study, BRANZ's Household Energy End-use Project (HEEP), found the average home used about 11,000 kWh of energy a year across all fuels, with the top fifth of homes using more than 14,400 kWh.
The pattern holds in most homes: heating and hot water dominate, while the gadgets people worry about, such as phone chargers and TVs on standby, are small. A home energy monitor proves it for your own house. If a heat pump is your biggest winter load, scheduling it properly makes a real difference; our guide to Mitsubishi heat pump Wi-Fi control covers the official app and a local ESP32 option.
Four ways to monitor home energy use
| Method | What you see | Cost | Installation | Best for |
|---|---|---|---|---|
| Retailer smart-meter data | Whole house, half-hourly, usually a day behind | Free | None | Everyone: start here |
| Sensor on the meter's LED | Whole house, near real time | Low (DIY parts) | Stick-on sensor, no wiring | Home Assistant tinkerers |
| Energy-monitoring smart plugs | One plug-in appliance at a time | Low per plug | Plug in | Fridges, heaters, dehumidifiers |
| CT clamp energy monitor | Whole house and individual circuits, live | Moderate, plus an electrician | Licensed electrician | Solar, EVs, detailed tracking |
Smart meter data in NZ: get your half-hourly usage
Most NZ homes now have a smart meter that records consumption every half hour, and many retailers show it in their app or online account, usually a day behind. That alone answers useful questions: what your house draws overnight, how much the heat pump adds on a frosty morning, and whether a time-of-use or free-hours plan would suit you.
You can also ask for the raw numbers. Under the Electricity Authority's rules, you can request up to two years of your consumption data from your retailer, and it must provide the data within five business days of a complete request. Ask for the standard EIEP13A file, a comma-separated format that opens in any spreadsheet; retailers may charge a reasonable fee only if you want a non-standard format.
The limits are that the data is whole-house only, and it arrives after the fact, so it will not tell you in real time that the dryer has just started.
Reading the meter's flashing LED
Smart meters have an LED that flashes in proportion to energy use, with the rate printed on the meter face, for example 1000 imp/kWh, which is one flash per watt-hour. An optical sensor held over the LED, wired to an ESP32 running ESPHome's pulse_meter sensor, turns those flashes into live watts and a kWh total. It is non-invasive, which makes it the favourite DIY option, but the meter belongs to your metering company, so never open or tamper with it; use removable tape or a clip, and check the meter box has room for it.
This is also the modern version of the classic "electricity meter over MQTT" project: an Arduino counting pulses and publishing them to an MQTT broker. ESPHome now does the same job with a few lines of YAML, and still supports MQTT if you prefer it to Home Assistant's native API.
CT clamp energy monitors explained
A current transformer (CT) is a split ring that clamps around a single conductor. Alternating current in the cable induces a much smaller, proportional current in the CT's winding, which the monitor measures. Nothing connects to the conductor itself, but the clamp must go around one active (or neutral) conductor, not a whole cable, or the two currents cancel out.
The SCT-013 current transformer
The YHDC SCT-013 series is the CT most DIY projects use. The SCT-013-000 is rated 100 A to 50 mA, with 2,000 turns and a 3.5 mm plug, and it has no built-in burden resistor: you add one so the output becomes a voltage your microcontroller can read. OpenEnergyMonitor's worked example gives a peak secondary current of 0.0707 A at 100 A, which means about 33 Ω on a 5 V Arduino and 22 Ω on a 3.3 V ESP32, plus a two-resistor divider to bias the signal to mid-supply. Voltage-output versions such as the SCT-013-030 (30 A to 1 V) have the burden built in and plug straight into an input.
Apparent power vs real power
A CT only measures current. Multiplying by an assumed 230 V gives apparent power, which overstates the draw of motors, heat pumps and electronics. For real power and power factor, the monitor also needs to measure the mains voltage, which is one reason commercial monitors connect to the supply rather than just clipping on.
Shelly EM and Shelly Pro EM-50
Shelly's energy meters are the most common ready-made CT monitors in NZ, sold by local smart-home and electrical suppliers. The Shelly EM measures two channels (clamps sold separately, up to 120 A per channel) and was NZ$161.99 at Lykalyte in September 2026. The DIN-rail Shelly Pro EM-50 has two 50 A channels, Wi-Fi, Ethernet and Bluetooth, a relay for switching a contactor, MQTT support, and stores at least 60 days of one-minute readings. Both work locally with Home Assistant, and both wire into the switchboard.
The switchboard is often in a garage or on an outside wall where Wi-Fi is weak. The Pro EM-50's Ethernet port helps, or add a Wi-Fi extender before the electrician arrives.
Emporia Vue in NZ
The Emporia Vue is popular in the United States, but it is designed for North American switchboards. When we checked in September 2026 we found it only on grey-import sites, not through NZ retailers or electrical wholesalers. For anything that lives in your switchboard, choose a monitor sold for the Australian and NZ market that your electrician is happy to fit.
DIY: ESP32, ESPHome and OpenEnergyMonitor
Makers can build their own with an SCT-013 clamp and an ESP32 running ESPHome's ct_clamp sensor, ideally through an external converter such as an ADS1115, or with a board based on a dedicated energy-metering chip. OpenEnergyMonitor, an open-source project, publishes complete monitor designs, firmware and the best CT documentation around. Our Arduino vs ESP32 vs Raspberry Pi guide explains which board to start with, and if you log readings on a Pi that might lose internet, fit a real-time clock so the timestamps stay right. The same switchboard rule applies to DIY hardware: a licensed electrician fits the clamps.
NZ safety rules: who can install an energy monitor?
Switchboards are off limits for DIY
WorkSafe's guidance for homeowners is blunt: never do any work on a switchboard apart from replacing fuse wire or fuse cartridges. Opening a switchboard to fit CT clamps or a DIN-rail meter exposes live parts, so it is licensed electrician work. Tenants and landlords cannot do electrical work in a rented home at all unless they are registered electrical workers.
That leaves plenty you can do yourself: request your smart-meter data, use energy-monitoring smart plugs, and fit an optical sensor to the outside of the meter's LED window. For a CT monitor, buy the hardware, then book an electrician; for a tidy job, ask them to label the clamps and note which circuit each one measures.
Home Assistant energy dashboard setup
Home Assistant has a built-in Energy dashboard that shows grid use, solar production, batteries, gas and individual devices by hour, day, week and month. It works from sensors that report energy in kWh; current versions also accept power sensors in watts, and the built-in integral helper can turn a watts-only sensor into kWh. Enter a fixed price per kWh, or point it at a sensor that tracks your tariff, to see costs.
- Shelly monitors are discovered on your network and add their energy sensors through the local Shelly integration.
- ESPHome devices such as a pulse counter or CT clamp build appear automatically once adopted.
- Energy-monitoring smart plugs can be added as individual devices, so the dashboard shows what share of the total each appliance uses.
- MQTT sensors from older Arduino projects still work, provided they publish a kWh total.
If Home Assistant is new to you, our home automation basics and smart home devices guide cover the groundwork. Adding solar later? CT monitoring on both the grid feed and the inverter shows how much of your own power you use, which matters for sizing, and our solar panel and battery calculator helps with that.
Electricity usage by appliance: finding the energy hogs
For anything with a plug, an energy-monitoring smart plug is the quickest answer: leave it on the appliance for a week and read the kWh. Our smart plug guide lists NZ models that measure energy. Hard-wired loads such as the hot water cylinder, oven and heat pump need a CT clamp on their circuit, or some detective work in your half-hourly data.
Two checks are worth doing first:
- Your overnight baseline. Find the lowest half-hour reading between midnight and 5 am. A reading of 0.3 kWh in half an hour means about 600 W running constantly, which is roughly NZ$1,840 a year at 35c/kWh. Fridges, freezers, heated towel rails, spa pools and always-on electronics are the usual suspects.
- Heated towel rails. A 100 W rail left on around the clock uses 876 kWh a year, about NZ$307 at 35c/kWh. A timer or smart switch that runs it for a few hours a day saves most of that.
Common mistakes with home energy monitors
- Clamping a whole cable. The active and neutral currents cancel out, so the monitor reads close to zero. Each clamp goes around a single conductor.
- Clamps facing the wrong way. That produces negative readings, which matters once you have solar and need to tell import from export.
- Trusting current-only readings. Without a voltage measurement, a monitor assumes 230 V and a power factor of one, overstating many appliances.
- Buying a monitor made for another market. North American units are built for different switchboards, and an NZ electrician may refuse to fit them.
- Overloading smart plugs. Many are rated at 10 A, about 2,300 W at 230 V, which a large heater running for hours can exceed. Check the rating first.
- Chasing standby watts while ignoring heating and hot water. A phone charger costs cents a year; a poorly set heat pump or cylinder costs hundreds.
Our take
- Start free: ask your retailer for your half-hourly data and look at the overnight baseline and the winter peaks.
- Add an energy-monitoring smart plug or two to check suspects such as dehumidifiers, heaters and old fridges.
- For live whole-house data, a Shelly EM or Pro EM-50 installed by an electrician is the simplest CT option, with local Home Assistant support.
- Tinkerers without switchboard access can get most of the value from an optical sensor on the meter's LED and ESPHome.
Prices and product availability were checked in September 2026 and change often. This guide is general information, not electrical advice; always use a licensed electrician for switchboard work. Nicegear is independent, sells nothing and has no paid placements.
Sources and further reading
- Doing your own electrical work – WorkSafe
- Access consumer data – Electricity Authority
- Electricity cost and price monitoring (Quarterly Survey of Domestic Electricity Prices) – MBIE
- Household Energy End-use Project (HEEP), Bulletin 486 – BRANZ
- CT sensors: interfacing with an Arduino – OpenEnergyMonitor documentation
- Shelly Pro EM-50 – Shelly Knowledge Base
- Home energy management – Home Assistant documentation
- CT clamp current sensor – ESPHome
FAQs
How can I monitor my home energy use in NZ?
Start with your retailer's app or a request for your half-hourly smart-meter data, which costs nothing. Add energy-monitoring smart plugs for individual appliances, and have an electrician fit a CT clamp monitor such as a Shelly EM if you want live whole-house readings.
Do I need an electrician to install an energy monitor?
Yes for anything inside the switchboard, including CT clamps and DIN-rail meters: WorkSafe says homeowners must not work on a switchboard apart from replacing fuses. Plug-in monitors, smart plugs and an optical sensor on the outside of the meter need no electrician.
Can I get my smart meter data in NZ?
Yes. You can request up to two years of consumption data from your retailer, which must supply it within five business days of a complete request. The standard EIEP13A file opens in a spreadsheet, and a charge applies only if you ask for a non-standard format.
What is an SCT-013 current transformer?
It is a clip-on current sensor widely used in DIY energy monitors. The SCT-013-000 turns up to 100 A in a cable into a 50 mA signal, which needs a burden resistor (about 22 ohms for a 3.3 V ESP32) before a microcontroller can read it.
Does Home Assistant have an energy dashboard?
Yes, it is built in and runs locally. It works with energy sensors from a Shelly meter, an ESPHome device, an MQTT sensor or energy-monitoring smart plugs, and it shows costs once you enter your price per kWh.
Is the Emporia Vue available in NZ?
We could only find it on grey-import sites in September 2026, and it is designed for North American switchboards. A monitor sold for the Australian and NZ market, such as a Shelly EM, is the safer choice for a switchboard install.
What uses the most electricity in a NZ house?
Heating and hot water. In BRANZ's HEEP study, space heating was 34% and water heating 29% of household energy, well ahead of refrigeration, lighting, cooking and other appliances.
