Standby Power & Appliance Duty Cycle Guides

Appliance Duty Cycle: Watts, Runtime and Electricity Cost

Imported guide · Source date 2026-09-07 · 5 min read

Duty cycle is the share of time an appliance draws its active power. Apply it once when using nameplate watts and plugged-in hours. Do not apply it again to annual energy-label kWh or metered energy, because cycling is already included.

Calculate fridge cost without double-counting duty →

Search for the running cost of almost any appliance and you will find the same calculation: take the wattage from the label, multiply by hours per day, divide by a thousand, multiply by your tariff. It is simple, it is widely repeated, and for a large class of appliances it is substantially wrong.

The problem is a single missing variable: duty cycle. Anything with a thermostat, a compressor or a heating element that regulates itself does not draw its rated power continuously. It draws full power in bursts, and does nothing in between. If you ignore that, you can overestimate an air conditioner by 30 per cent and a refrigerator by 400 per cent.

What duty cycle actually means

Duty cycle is the fraction of time an appliance spends actually drawing power while it is switched on. A 1,500 W space heater with no thermostat runs at 100 per cent duty — it draws 1,500 W the whole time. A 1,500 W space heater with a thermostat, in a room that reaches temperature, might run at 45 per cent duty: it heats hard, switches off, cools, and heats again.

Both heaters have the same label. Over an eight-hour evening one uses 12 kWh and the other uses 5.4 kWh. That is the entire difference between an accurate estimate and a useless one.

Which appliances have a duty cycle

The dividing line is whether the appliance regulates itself against some target. If it does, it cycles. If it just runs, it does not.

The refrigerator: the worst offender

A fridge is the appliance most often estimated wrongly, because it is the one people most confidently describe as "on 24 hours a day". It is plugged in 24 hours a day. Its compressor runs for perhaps six of them.

Take a 150 W fridge. The naive calculation gives 150 W × 24 h = 3.6 kWh a day, or 1,314 kWh a year. The real figure for a modern 300-litre fridge-freezer is 250 to 400 kWh a year. The naive answer is out by a factor of three to five.

How to estimate duty cycle for your own appliance

There are three approaches, in descending order of accuracy.

1. Measure it

A plug-in energy meter costs very little and settles the question completely. Leave it on the appliance for a week, read the cumulative kWh, and divide by seven. This bypasses duty cycle entirely — you get the real number.

2. Time the cycles

Listen to the appliance for half an hour. Note how long the compressor or element runs and how long it is silent. A fridge that runs for eight minutes and rests for twenty-two has a duty cycle of 8 ÷ 30, or 27 per cent.

3. Use a table

The table above gives realistic starting points. They are ranges rather than single numbers because duty cycle depends on your conditions, not just the appliance.

What changes an appliance's duty cycle

• Ambient temperature. A fridge in a 35°C kitchen cycles far more than the same fridge in an 18°C one. This is why summer bills rise even when nothing changed.
• Insulation and sealing. A worn door gasket on a fridge, or a draughty room for a heater, raises duty cycle directly.
• Setpoint. Every degree lower on a fridge or AC thermostat means more running time to hold it.
• Load. A full freezer cycles less than an empty one because the frozen mass holds temperature. A fridge opened constantly cycles more.
• Appliance sizing. An oversized AC cycles briefly and often; an undersized one runs at 100 per cent and never reaches setpoint.

Where duty cycle does not apply

Do not apply a duty cycle to appliances that draw a steady load. A ceiling fan at 75 W draws 75 W. An LED panel at 18 W draws 18 W. A television draws what its brightness setting demands, continuously, with no cycling. Applying a duty cycle to these gives you an answer that is wrong in the other direction.

Motors are a partial exception. A pump or a fan draws its rated power while running, but starting draws a surge several times higher for a fraction of a second. That surge matters for cable and breaker sizing; it barely registers on the energy bill.

Putting it together

The correct calculation for a self-regulating appliance is:

For a 1,500 W air conditioner at 70 per cent duty, run eight hours a day: 1,500 × 0.70 ÷ 1,000 × 8 = 8.4 kWh. The naive calculation would have said 12 kWh — an overestimate of 43 per cent, which on a season of use is a meaningful amount of money.

Every calculator on this site includes a duty cycle field for exactly this reason. The default is set to a realistic value for each appliance rather than to 100 per cent, which is why our figures often come out lower than other tools' — and closer to what your meter actually records.

Calculate it yourself

Imported source date: 2026-09-07. Review details have not been independently verified.

How to Do a Home Energy Audit — Room by Room

Imported guide · Source date 2026-08-20 · 13 min read

You do not need a professional to find where your electricity goes. An afternoon, a plug-in meter and this checklist will identify most of what is on your bill.

Most advice about reducing electricity bills is generic: switch to LEDs, unplug chargers, use a lower thermostat setting. Some of it helps and some of it is noise, and the only way to tell which is which in your home is to measure.

This is a practical audit you can complete in an afternoon. It requires a plug-in energy meter, access to your electricity meter, and a willingness to write things down.

Before you start: establish your baseline

Read your electricity meter and note the number and the time. You will read it again at several points. Then find your last twelve months of bills, or your online usage history, and note your average daily consumption in units.

A typical one-bedroom flat runs 5 to 8 units a day. A family house with electric cooking and hot water might run 15 to 30. An all-electric house with a heat pump or an EV can run 40 or more. Knowing your number tells you whether you have a problem or just an expensive tariff.

Step 1: The standby test

This is the single most revealing measurement in the whole audit, and it takes ten minutes.

• Switch off or unplug everything you can — lights, TV, computers, kitchen appliances.
• Leave running only the things you cannot switch off: fridge, freezer, router, alarm.
• Read the meter. Wait exactly one hour. Read it again.
• The difference is your baseline load — what your house consumes doing nothing.

A well-managed home shows 0.10 to 0.25 units in that hour. Above 0.4 units means something substantial is running that you have not accounted for. Multiply by 8,760 to see the annual cost of your baseline: 0.3 units an hour is 2,628 units a year, which is a very large bill for nothing.

Step 2: The living room

The set-top box is often the worst item in the room because its standby draw is barely lower than its running draw, and it is on 24 hours a day. A box drawing 20 W continuously costs about 175 units a year.

Step 3: The kitchen

The kitchen usually holds your largest single continuous load and your largest intermittent ones.

• Fridge and freezer. Put the meter on for 24 hours. Anything over 1.5 units a day for a normal fridge-freezer suggests worn seals, a dusty condenser coil, or an ageing compressor.
• Check the door seal with a banknote: close the door on it, and if it slides out with no resistance the gasket has failed.
• Vacuum the condenser coils at the back or underneath. Dust there directly raises running time.
• Check the thermostat. Fridge at 4°C, freezer at −18°C. Colder than that costs money and preserves nothing better.
• Note your cooking mix. Oven, hob, microwave, air fryer and kettle — how often each is used matters more than their wattage.

Step 4: Hot water

In many homes water heating is the largest or second-largest item on the bill, and it is almost invisible because it happens inside a cupboard.

• Find out whether your water heating is electric, gas or solar. If electric, this is likely your biggest target.
• Check the tank thermostat: 55 to 60°C is right. Higher increases standby loss and scale.
• Feel the tank and the first metre of pipe. If they are warm, they are losing heat you paid for. A tank jacket and pipe lagging pay back within months.
• If there is a timer, use it. Heating for two hours before peak demand costs far less than holding temperature all day.
• Check for a dripping hot tap. A hot drip costs both water and the energy to heat it.

Step 5: Heating and cooling

Whatever your climate, this is where the seasonal swing in your bill comes from.

• Note every heater and air conditioner, its wattage, and roughly how many hours a day it runs in season.
• Check air conditioner filters. A clogged filter raises running time measurably for the same setpoint.
• Look for a reverse-cycle capability on your AC. If it has one, you already own the cheapest electric heating in the house.
• Check for draughts around windows and doors with the back of your hand on a windy day.
• Note which rooms you heat or cool that nobody occupies.

Step 6: Lighting

Count fittings by type, not by room. Multiply each type's wattage by its daily hours.

If you still have incandescent or halogen fittings anywhere used more than an hour a day, that is the highest-return replacement in the house — usually paying back in under a year.

Step 7: The hidden loads

These are the items that never appear on a checklist but often appear on the bill.

• Water pump. A pump cycling on a leak or a failed foot valve can add hundreds of units a month.
• Garage or basement freezer. Frequently forgotten, frequently ancient, frequently the least efficient appliance in the house.
• Towel rail or underfloor heating. Often left permanently on with no thermostat.
• Aquarium, terrarium or pond pump. Continuous loads with heaters and lighting attached.
• Home office equipment. A desktop, two monitors and a printer left on overnight is 100 W of nothing.
• Old inverter or UPS. Trickle-charging inefficiently around the clock.
• Outdoor and security lighting. Often halogen, often on a broken timer.

Step 8: Rank by annual cost, not by wattage

Now convert everything to annual units and sort the list. This is the step that turns an audit into a plan, and it routinely surprises people: a 2,000 W kettle used ten minutes a day matters less than a 20 W set-top box left on permanently.

Step 9: Fix in order of payback

Work down your ranked list, and for each item estimate what it would cost to fix and what it would save. Do the free things first — switching off fast-start, fixing thermostat settings, using timers, unplugging the forgotten freezer. Then the cheap things: LED replacements, pipe lagging, door seals. Only then consider appliance replacement.

Re-read your meter a month after making changes and compare the daily average against your baseline. If the number has not moved, your estimate of where the electricity was going was wrong — go back to the standby test and look harder.

Calculate it yourself

Imported source date: 2026-08-20. Review details have not been independently verified.

Standby Power Cost: How to Calculate Vampire Energy Use

Imported guide · Source date 2026-09-07 · 4 min read

Standby power adds up because small loads can run all year. A constant 5 W load uses 43.8 kWh per year: multiply that by your tariff to price it. Measure each device rather than assuming a fixed percentage of every household bill.

Calculate a standby load at 24 hours/day →

Standby power — also called vampire draw or phantom load — is the electricity consumed by devices that are switched off, or that appear to be. Studies across several countries have consistently put it at 5–10% of residential electricity consumption. In a home spending $1,200 a year, that is $60 to $120 spent on nothing at all.

The reason it goes unnoticed is arithmetic. Nobody worries about 15 watts. But 15 watts running for 8,760 hours a year is 131 kWh — more than most people's entire annual laundry consumption.

Real standby wattages

How to find your own phantom load

The midnight meter test

Switch off everything you can consciously control — lights, TV, computers — leaving only the fridge and things you cannot unplug. Read your meter, wait an hour, read again. Subtract the fridge's expected consumption (roughly 0.05 kWh in an hour) and what remains is your baseline phantom load. Most homes find somewhere between 50 and 100 watts.

The plug meter sweep

A plug-in energy meter gives you the per-device answer in an afternoon. Work through the entertainment wall, the office desk and the kitchen counter, noting anything above 3 W in standby. Those are your targets.

What to do about it

• Switched power strips on the TV wall and the office desk. One switch kills five vampires, and it takes thirty seconds to install.
• Smart plugs with schedules for anything that has no business drawing power between midnight and 6 am.
• Turn off networked standby on consoles unless you genuinely need overnight downloads — this setting alone is often 10–15 W.
• Disable 'instant on' on soundbars, AV receivers and smart TVs. The two-second start-up delay is a fair trade for 175 kWh a year.
• Unplug the second fridge in the garage if it holds four drinks. A spare old fridge is frequently the single largest wasted load in a house.
• Do not bother unplugging modern chargers. Under 0.5 W is genuinely negligible; spend the effort on the 15 W items instead.

The realistic prize

A typical household that eliminates 60 W of unnecessary standby saves 526 kWh a year — around $89 in the US, £130 in the UK or ₹4,200 in India, every year, permanently, for the cost of two power strips. Few efficiency measures have a better return.

Model your own always-on devices with the appliance energy cost calculator by setting hours per day to 24 — the annual figure is usually a surprise.

Calculate it yourself

Imported source date: 2026-09-07. Review details have not been independently verified.