A smart device saves money only when the energy it switches off exceeds the energy it uses to stay online. Most Wi-Fi plugs, switches and thermostats draw roughly 0.5 to 2 watts around the clock, so the load you control matters more than the gadget.
Put smart controls on heating and cooling, large standby clusters, forgotten lights and sprinklers first. Skip them on single LED lamps, where the device can cost more to run than it saves.
The break-even math: standby watts versus watts you cut
One watt drawn all year equals 8.76 kilowatt-hours (1 W × 8,760 hours ÷ 1,000). At 17 cents per kWh, close to a typical US residential rate, that is about $1.50 a year for every watt.
Use the rate printed on your own bill.
The test is simple: watts cut × hours cut per year must beat the device’s own standby watts × 8,760. Standby varies widely by product, which is why measured standby tables for household electronics are worth a look before you buy.
Three cases at 17 cents per kWh:
- Smart plug on a 5 W LED desk lamp you would otherwise leave on two extra hours a day: saves 3.7 kWh a year, while the plug’s 1 W draw uses 8.8 kWh. You lose about $0.90 a year.
- Same plug on an entertainment center whose TV, soundbar and console measure 15 W on standby, cut 18 hours a day: 98.6 kWh saved minus 8.8 kWh for the plug nets about $15 a year. A $12 plug pays back in under a year.
- Heavy-duty plug on a 500 W window air conditioner that now runs three fewer hours a day over a 100-day summer: 150 kWh saved, about $24 net after the plug’s own draw. It pays back in one season.
Measure before you buy. A plug-in watt meter ($15 to $30) or an energy-monitoring smart plug shows the real standby draw of a TV cluster or desk setup in a few minutes.
Standby draw and payback by device
| Device type | Own standby draw (typical) | Best target load | Upfront cost | Realistic payback |
|---|---|---|---|---|
| Smart thermostat | 1–3 W (from the HVAC’s 24V supply) | Central heating and cooling in a home with irregular hours | $100–$250 | 2–5 years; faster with a utility rebate |
| Smart plug, standard | 0.5–1.5 W | Entertainment center or desk with 10 W or more of standby | $8–$20 | Under 1 year; never on a single LED lamp |
| Smart plug, heavy-duty (15 A) | 0.5–2 W | Window AC within the plug’s rating | $15–$30 | One cooling season |
| Smart power strip (control outlet) | 0.5–2 W | TV or computer plus peripherals | $25–$50 | 1–3 years |
| Smart switch with occupancy sensing | 0.3–1 W | Garage, basement or laundry lights often left on | $25–$60 | 2–10 years, depending on hours saved |
| Smart bulb | 0.2–1 W | Lights you want dimmed or scheduled | $8–$20 per bulb | Rarely pays back on energy alone |
| Whole-home energy monitor | 2–5 W | Homes with a high or unexplained bill | $150–$300 plus $150–$400 electrician | Only if you act on what it finds |
| Smart irrigation controller | 2–4 W | Automatic sprinklers on a clock timer | $100–$300 | 1–2 seasons in dry climates (water bill) |
| Motorized shades | Under 1 W per motor, plus any hub | Sun-baked east and west windows | $200–$600+ per window | Comfort purchase; rarely pays back |
Standby figures are typical ranges for Wi-Fi and hub-based products; check the maker’s published spec or measure your own. Costs are typical retail ranges before rebates.
Smart thermostats: where the 8% comes from
Heating and cooling is the largest load in most homes, so a small percentage cut there outweighs everything else on this list. ENERGY STAR’s field data shows certified smart thermostats save an average of 8% on heating and cooling bills, about $50 a year.
The mechanism is setback. The Department of Energy estimates that turning the thermostat back 7° to 10°F for 8 hours a day saves up to 10% a year on heating and cooling.
A basic programmable thermostat captures most of that if your schedule never changes. A smart model earns its premium when hours shift or nobody remembers to adjust it; our guide to choosing a smart thermostat for energy savings compares features and wiring needs.
Take a home with a gas furnace and central air that sits empty weekdays from 8 to 6 and spends $900 a year on heating and cooling. An 8% cut is $72, so a $150 thermostat pays back in about two years.
A thermostat cannot fix a drafty house, so seal leaks first with our room-by-room insulation guide.
Smart plugs: the loads worth switching
Good targets are clusters with real standby draw: a TV with soundbar and console, a desktop with monitors, printer and speakers, or a window AC you want off while you are out. Group them so one schedule cuts the whole cluster.
A smart power strip with a control outlet does this without an app. When the TV or computer on the control outlet shuts down, the strip cuts power to the peripherals.
Leave these off smart plugs:
- Space heaters. Plug them directly into a wall outlet, never into a smart plug or power strip, and use the heater’s own thermostat and timer.
- Refrigerators, freezers and medical equipment. Cutting their power risks spoiled food or worse.
- Your router and modem. Every other smart device drops offline with them.
- Single LED lamps and idle phone chargers. Their draw is too small to beat the plug’s.
Before plugging in any high-draw appliance, compare the wattage or amps on its nameplate with the plug’s rating, and stay comfortably below it.
Lights, shades and monitors: mostly comfort, sometimes savings
The bulb matters more than the control. Swapping a 60 W incandescent for a 9 W LED cuts 51 W every hour it burns, while scheduling that LED saves a few watts; our LED vs CFL comparison runs the numbers.
Occupancy switches pay where lights get forgotten. A garage with four 15 W LED fixtures left on five extra hours a day wastes about 110 kWh, roughly $18 a year, so a $40 switch pays back in just over two years.
Whole-home monitors clamp sensors around the service conductors in your main panel, which stay live even with the main breaker off. Always hire a licensed electrician for this installation.
A monitor saves nothing by itself. Its value is finding the specific culprits, such as an aging second fridge in the garage or a dehumidifier running nonstop, that you then repair, replace or unplug.
Irrigation controllers: the savings land on the water bill
Replacing a clock timer with a WaterSense-labeled weather-based controller cuts outdoor watering because it skips cycles after rain and adjusts run times by season. Many water utilities offer rebates on labeled models.
Soil-moisture controllers take a different route, watering only when the root zone is dry. EPA WaterSense reports that soil-moisture-based controllers cut water use for the average home with an automatic sprinkler system.
Payback is fastest in hot, dry regions with large lawns. Pair either type with the fixes in our water conservation guide, such as repairing broken heads that waste water whatever the schedule.
Fixing the three problems that stall installs
The thermostat has no C-wire
Switch off power to the furnace or air handler at its breaker or service switch before removing the old thermostat. The common wire supplies continuous 24VAC; without it, some smart thermostats drain their batteries or drop offline.
Google’s Nest support explains how a common wire or a power adapter fixes these power problems. Look for an unused wire folded behind the wall plate and at the furnace control board before buying an adapter kit.
If no spare wire exists, use the maker’s adapter or have an HVAC technician run one. Call a pro outright for heat pumps with auxiliary heat, dual-fuel or multi-stage systems, where miswiring can damage equipment.
The switch box has no neutral
Turn off the breaker and confirm the box is dead with a non-contact voltage tester. Most Wi-Fi switches need a neutral, usually a bundle of white wires capped together at the back of the box, to power their radio.
If you find only two wires on the old switch (a switch loop), buy a no-neutral model rated for your bulbs or call a licensed electrician. Never connect a neutral terminal to the bare ground wire.
The device won’t join or stay on Wi-Fi
Most smart plugs and switches connect only on 2.4GHz. Routers that broadcast both bands under one name can block setup, so TP-Link’s troubleshooting guide recommends separating the 2.4GHz and 5GHz networks on dual-band and mesh routers.
A device that keeps dropping offline also misses its schedules, erasing the savings. Add a mesh node or move the router closer before blaming the device.
Keeping the savings over the device’s life
- Review schedules each season. Setback temperatures that suit January often waste energy in July.
- Install firmware updates and favor devices with local control, so automations keep running if a company’s app shuts down.
- Skip hubs you don’t need. A hub adds its own 1 to 3 W of standby to the math.
- Maintain the equipment being controlled. A smart thermostat can’t offset a clogged filter; follow our HVAC maintenance guide.
