Standby and Phantom Loads: What Is Worth Chasing

Why this matters

When a bill jumps, somebody in the house starts unplugging phone chargers. It feels productive and it almost never moves the bill. Meanwhile a twenty-year-old freezer in the garage, a dehumidifier left on continuous, or a heated device nobody thinks of as an appliance runs every hour of every day. A tech who can tell the customer which of their always-on loads matter, with the arithmetic to show it, gives better advice in five minutes than a printed list of tips gives in a year.

Standby, phantom and continuous: three different things

The words get used loosely, so pin them down before you talk to a customer.

• Standby load is what a device draws while it is switched off or idle but still plugged in: the clock on a microwave, the receiver waiting for a remote, a charger with no phone on it. The device is not doing its job; it is waiting to.
• Phantom load is the common name for the same thing, usually said with the implication that it is hidden. Treat the two as one category.
• Continuous load is a device that is actually working all the time, or cycling on and off all day: a refrigerator, a freezer, a dehumidifier, a well pressure system, an aquarium heater, a hot tub holding temperature. This is not standby. It is real work, and it is where most of the always-on energy in a house goes.

The distinction matters because customers lump all three together under "things that are plugged in", then chase the smallest one because it is the easiest to unplug.

The one formula

For anything that draws power around the clock:

kWh for the period = average watts x 24 x days / 1000

cost for the period = kWh x the rate per kWh on the bill

It is the same watts-times-hours method the U.S. Department of Energy's consumer guidance uses for appliances and electronics.

The word that does the work is average. A refrigerator's compressor does not run all the time, so its average draw is far below its running draw; a phone charger draws almost nothing when the phone is off it. Plug a running wattage into this formula and you overstate the cost, often by several times. See related: Duty Cycle: Why Run Hours, Not Clock Hours, Set the Cost.

Two shortcuts worth memorizing, both straight from the formula:

• Every watt of continuous load is about 8.8 kWh a year (1 x 24 x 365 / 1000 = 8.76).
• Every 100 watts of continuous load is 72 kWh in a 30-day month (100 x 24 x 30 / 1000 = 72).

With the second one you can size any always-on load against the customer's bill in your head.

What small standby actually adds up to

Modern chargers, set-top boxes in deep standby, and most electronics that meet current efficiency programs draw well under a few watts each while waiting, and a charger with nothing attached is commonly a fraction of a watt. Some devices are worse than their category suggests: a game console set to an instant-on mode, an older audio receiver, a desktop computer that never really sleeps, a cable or satellite box that keeps its tuner and disk running. Those can sit at tens of watts.

The honest way to talk about the small stuff is in aggregate. A household with a typical spread of electronics may total somewhere in the tens of watts of true standby. That is real but modest, and most of it sits on devices the customer will not unplug anyway because they want the clock, the remote or the fast start.

Worked example: the family that unplugged everything

A customer calls about a 900 kWh bill for a 30-day period and says they have already unplugged every charger in the house. You ask them to read a plug-in watt meter on a few things over a weekend (a meter that totals kWh over hours, not a snapshot of watts). They report back, with figures we will treat as theirs:

• Fifteen small standby devices (chargers, a TV, a soundbar, a set-top box, a printer, a coffee maker): about 30 W together on average.
• A garage refrigerator, roughly 25 years old, kept for drinks: 2.9 kWh over 24 hours, which is 2.9 x 1000 / 24 = about 121 W average.
• A basement dehumidifier set to continuous because the humidistat "never seemed to shut it off": 7.2 kWh over 24 hours, 300 W average.

Run each through the formula for 30 days.

Check the third row against the meter reading: 7.2 kWh a day x 30 days is 216 kWh, which matches. The second row: 2.9 x 30 = 87.0, against 87.1 from the rounded wattage; same answer.

What the table says:

• Unplugging all fifteen small devices, permanently, saves at most 21.6 kWh a month, which is 21.6 x the rate on the bill. In practice it saves less, because the TV and the coffee maker go back in within a week.
• The garage refrigerator alone is four times the whole standby category (87.1 / 21.6 = 4.0). It is also the kind of load customers forget. A unit that old commonly uses a multiple of what a current one of similar size does, so the option worth putting to the customer is whether they need it at all, or whether it can run only in summer.
• The dehumidifier is a quarter of the bill. That is the one worth the customer's attention, and the question is not whether to unplug it but why it runs continuously. A basement that genuinely needs that much moisture removal has a water source worth finding, and a dehumidifier set to continuous rather than to a humidity setpoint removes moisture the room may not need removed. Setting it to a humidistat target, commonly somewhere around 50 percent relative humidity in a basement, lets it cycle. Whether a stubborn reading points to a leak, a grade problem or a vent issue is a separate diagnosis; route it to whoever does moisture work.

Three loads together are 324.7 kWh, 36 percent of the 900. The fifteen devices the customer unplugged are the smallest line on the table.

The loads that are actually worth chasing

The useful sort is by average watts, not by how many devices there are. As a starting point you can tune to the house: anything averaging above about 50 W around the clock (36 kWh a month) is worth a conversation; anything under about 10 W is not worth the customer's effort unless it is one of many. The ones that cross the line most often:

• Second refrigerators and chest or upright freezers, especially old ones and especially in a hot garage, where the compressor runs far longer than it would indoors.
• Dehumidifiers on continuous mode, or in a space with an unsolved water problem.
• Heated devices: heat tape or de-icing cable left plugged in through summer, a waterbed heater, a heated towel rack on all day, a large aquarium's heater and lights, a reptile enclosure, a pet bed or livestock waterer heater.
• A hot tub or swim spa holding temperature, particularly with a damaged or waterlogged cover, which lets heat out faster than the heater was meant to make it up.
• Pumps that run or cycle all day: a pool pump on a long timer, a pond or fountain pump, a hot water recirculation pump with no timer or demand control, a sump pump in a high water table.
• Computers that never sleep, including a home server, a network storage box, or a machine doing continuous high-load computing, which can draw hundreds of watts.

Measuring the small numbers honestly

Instantaneous watt readings at very low loads are the least trustworthy number a plug-in meter gives, because most of them are least accurate near the bottom of their range. For anything under a few watts, read the accumulated kWh over a day or more and divide by the hours. That averages out cycling and the meter's low-end error both.

For the big continuous loads, a full day is the minimum, and a refrigerator or dehumidifier is better read across two or three days because its run time follows temperature and humidity. A freezer measured on a cool night will read low.

If the customer cannot measure each device, the whole-house floor answers the aggregate question: the lowest overnight hour on interval data, or a reading at the meter with known loads off, sets an upper bound on everything that runs continuously. See related: Smart Meter Interval Data: What the Hourly Record Shows, and How to Run a Whole-House Baseline Test at the Electric Meter.

What not to say

Do not tell a customer that unplugging chargers will lower their bill noticeably, and do not hand over a list of tips with no numbers. Both teach them that energy advice is folklore, and the next time a tech tells them the dehumidifier is a quarter of their bill, they will hear it as folklore too. Give the one or two loads that matter, the kWh each one is responsible for, and the cost written as kWh x their rate. See related: Teaching Energy and Water Saving Habits Honestly.

Do not promise a specific monthly saving either. The dehumidifier's 216 kWh is what it used during the measurement days; set to a humidistat in a drier month it may use a fraction of that, and in a wet spring more. Say what was measured and under what conditions. See related: Savings Claims Without Overpromising: The Honest Language.

A safety note that belongs in any walk-around: heat tape and de-icing cable that is cracked, kinked, taped over or plugged into an extension cord is a fire risk, not just an energy load. Tell the customer to unplug it and leave it unplugged until an electrician has looked at it, and do not handle a damaged run yourself while it is energized.

References

• See related: Teaching Energy and Water Saving Habits Honestly
• See related: The Loads a Customer Forgets They Own
• See related: Why a Bill Rises: The Causes That Are Not the New Equipment
• See related: How to Measure Real Watts Instead of Trusting the Nameplate
• U.S. Department of Energy consumer guidance on estimating appliance and home electronic energy use