What your in-home display is actually showing you

Your in-home display (often just called the IHD) is the small screen that came with your smart meter. It talks wirelessly to your electricity meter, and usually to your gas meter too, and refreshes every few seconds. Most displays show the same core pieces of information, even if the buttons and colours differ between models.

• Now: your current electricity use in watts (W) or kilowatts (kW). This is an instant snapshot, like a speedometer.
• Today: energy used since midnight, in kilowatt-hours (kWh). This is the odometer — the number that actually ends up on your bill.
• Cost: usually today's spend in pounds and pence, and sometimes an hourly or weekly figure.
• Traffic light or coloured dial: green, amber and red bands that show whether you are using a little, a moderate amount or a lot compared with a preset threshold.
• Gas: many displays also show gas use in kWh, though it updates far less often — often every half hour rather than every few seconds.

One thing worth knowing: the cost figure on most displays covers energy only. Your daily standing charge is normally not included, so the total on your bill will be a little higher.

Watts and kilowatt-hours: the difference that matters

These two numbers confuse almost everyone at first, and understanding them is the key to using your display well.

Watts tell you how fast you are using energy right now. Kilowatt-hours tell you how much energy you have used in total. A 3 kW immersion heater running for one hour uses 3 kWh. The same heater running for 20 minutes uses 1 kWh. The wattage is the same in both cases; only the time changes.

This is why the instantaneous figure can look alarming — a shower can pull 9 kW or more — but it only costs real money for as long as it runs. Conversely, a device drawing a steady 150 W around the clock adds up to 3.6 kWh a day, which is often more than people expect.

Reading the meter itself, not just the display

The display is for day-to-day awareness. The meter is the official record. It is worth learning how to read it, because the two can disagree slightly, and a display can lose its connection to the meter.

• Your electricity meter shows a running total in kWh, usually to one decimal place. That number only ever goes up.
• If you have an Economy 7 or similar two-rate tariff, there will be two registers — one for daytime units and one for night-time units.
• To measure a period yourself, note the reading and the date and time, then read it again a week later and subtract. That gives you a true weekly figure, unaffected by any display glitches.
• Older-style meters with a flashing red light typically flash once per watt-hour, so 1,000 flashes equals 1 kWh. Counting flashes for a minute is a surprisingly accurate way to check what a circuit is drawing.

Using the display to find your big loads

The most useful habit is to watch the "now" figure while you switch things on and off. You will quickly learn which appliances actually move the needle.

• Kettle: around 2.5 to 3 kW, but only for two or three minutes.
• Electric shower: 8 to 10.5 kW while running — usually the single biggest load in a home.
• Tumble dryer: 2 to 3 kW for an hour or more, so a heavy user of energy overall.
• Oven: 2 to 2.5 kW while heating, then cycling on and off to hold temperature.
• Fridge freezer: only 100 to 150 W, but running most of the day and night.
• Standby: each device might draw 1 to 15 W. Individually trivial, but a houseful of them can add up to 100 W or more, which is roughly 0.9 kWh a day.

A practical trick: turn everything off at the wall, note the baseline figure, then bring circuits back one at a time. Anything that pushes the reading up by more than a few watts when nothing is in use is worth investigating.

Building a simple daily routine

You do not need to stare at the display all day. A short, regular check is far more effective.

• Morning: glance at yesterday's total in kWh. This is your benchmark.
• Early evening: check today's running total against the same point yesterday. A spike usually has an obvious cause — a longer shower, the tumble dryer, the heating pump working harder.
• Weekly: note the total every Sunday and keep a short list. Comparing like with like across weeks tells you whether changes are working.
• After any change: if you shorten showers, dry washing on a rack or switch to LED bulbs, check the following week's figure. Seeing the number fall is genuinely motivating.

If the cost shown looks wrong, open the settings menu and check the unit rate. Displays can lag behind a tariff change, and some let you enter the rate manually. A quick correction makes everything else on the screen trustworthy.

Getting more from the numbers

Once you know your baseline, the display becomes a planning tool rather than a novelty. If you are on a time-of-use tariff, use it to see how much of your use sits in the expensive window — then shift what you can, such as the washing machine or dishwasher, into the cheaper hours. If you have solar panels, the "now" figure will sometimes show a negative value or an export figure, which is your cue to run appliances while the sun is doing the work.

Above all, treat the display as a guide, not a verdict. It is there to show you patterns, and patterns are where the savings live.