How can you find what uses the most electricity at home?

Start with the home's total demand, then narrow the search only as far as the decision requires. Smart-meter data finds the time of a problem. Circuit monitoring locates the part of the installation. A plug-in meter tests one suitable appliance.

That sequence avoids buying a monitoring system to answer a question your existing meter may already resolve. It also prevents a common mistake: treating a recognisable shape on a graph as proof that a particular appliance caused it.

Use the smart meter to find the time

For a Portuguese property connected to a smart grid, the E-REDES online service provides a load profile in 15-minute intervals. ERSE explains that smart-grid services include daily data availability and may include consumption and contracted-capacity alerts.

This history is good at timing. Look for a steady overnight baseline, a repeated rise before anyone arrives home, or peaks that follow a familiar household routine.

It is less good at attribution. Each interval combines every load that operated during those 15 minutes. If the aim is to compare tariff periods or check when grid imports begin despite solar generation, this may be enough. If the aim is to identify one appliance, move closer to the load.

Add detail where it changes the answer

Three levels are useful, each with a different resolution and installation requirement:

• Whole-property meter. Shows total demand and helps compare days, times and tariff periods. It is the natural starting point and needs no extra sensors.
• Circuit monitoring. Sensors at the distribution board can separate heating and cooling, kitchen loads, pool equipment or EV charging. They require suitable space, compatible equipment and installation by a qualified technician.
• Appliance monitoring. A plug-in meter is practical for equipment connected through a socket. It is not suitable for fixed loads and must stay within the manufacturer's rated limits.

A plug-in meter is a useful diagnostic tool, not a universal shortcut. Fixed heating, an oven or an EV charger need a different approach. Circuit data is also more useful when the real question is whether several large loads overlap, rather than how much one device uses over a month.

Build a baseline you can trust

One reading is easy to misinterpret. Heating and cooling depend on outdoor conditions. Kitchen demand changes with occupancy. A pump may run longer one day because of a schedule or condition that does not recur.

Collect several ordinary days that include occupied and empty periods. Keep a short note of relevant events such as EV charging, heating schedules or unusually heavy cooking. A small amount of context often explains more than another month of unlabelled data.

When testing a change, alter one variable at a time. Changing a temperature setting, moving a schedule and switching off another appliance on the same day will change the graph, but it will not show which action mattered.

Stop measuring when the action is clear

Permanent dashboards are not the goal. Keep monitoring where changing demand matters, and use temporary measurements for questions that can be settled once. The evidence may support:

• Correcting a schedule that leaves a load running unnecessarily.
• Preventing high-power equipment from operating at the same time.
• Automating a rule around time, occupancy or surplus solar generation.
• Investigating equipment whose demand changed without a change in use.
• Sizing self-consumption around the real load profile rather than a monthly bill.

A battery for self-consumption, for example, should be assessed against surplus generation and demand outside solar hours. A monthly total hides that relationship.

For home energy management, the useful level of detail depends on the decision and the available infrastructure. Circuits that affect supply capacity, self-consumption or comfort are normally the ones worth monitoring continuously. Everything else should earn its sensor.

Assess monitoring for my home. Include whether you have a smart meter or solar panels, and which equipment or times of day you want to investigate.