The phrase “smart home” appears in nearly every contemporary residential brief. It usually means a particular collection of consumer technologies: voice assistants, app-controlled lighting, networked thermostats, video doorbells, motorised blinds, smart locks, fridges that talk to your phone. The implication is that this collection is, in some way, sustainable — that the chips and sensors and apps save energy.
Most of them don’t.
What actually moves an energy bill
If you list the things that determine how much energy a home uses, in rough order of impact:
- The building envelope. Insulation, windows, airtightness. Most of the heat your house loses goes through these. See on the passive house
- The mechanical systems. Heating, cooling, hot water. Their efficiency and how well they’re zoned
- Occupant behaviour. Thermostat settings, window habits, hot-water use, equipment left on
- The big appliances. Fridge, washer, dryer, dishwasher, cooker, electric vehicle if any
- Lighting. Less than it used to be, because LEDs are now everywhere
- The plug load. Every device that’s on or in standby. Modems, set-top boxes, voice assistants, monitor screens, smart speakers
Smart-home technology sits almost entirely in items 3 and 6. It can help with occupant behaviour (item 3) when implemented intelligently. It adds to plug load (item 6) whether you want it to or not. Whether the help outweighs the cost depends on what specifically you install.
The hidden plug load
Every smart device on a network draws power continuously. Most modern smart-home devices use 1–5 watts in standby, all the time. That sounds small. Multiplied across a fully smart home — thirty to fifty connected devices is now ordinary — it can add up to 100 watts of constant draw, or roughly 900 kWh per year. The same as running a small fridge that does nothing.
The International Energy Agency has tracked this category for two decades; standby and networked-device load has grown from a few percent of household electricity to a meaningful share, and continues to grow as more devices acquire chips.
The smart things that genuinely help
Some smart technologies are real net wins. The criteria: they reduce a much bigger load than they themselves add, and they don’t require behavioural attention to keep working.
Learning thermostats. Nest, ecobee, Tado. A well-implemented learning thermostat reduces heating-and-cooling energy by roughly 8–15% in studies, by setting back temperatures when nobody’s home and learning the building’s thermal response. The savings overwhelmingly exceed the device’s own draw. ENERGY STAR certifies the better models.
Occupancy-based lighting. In rooms that get left lit (hallways, bathrooms, laundries), a motion-and-daylight sensor at the fitting is a small intervention with real payback over a building’s life. The sensor itself draws less than a tenth of a watt and the cumulative left-on-lights savings are measurable.
Zoned heating control. The single biggest residential opportunity in older buildings. A house heated as one zone wastes heating on rooms that aren’t occupied. Per-room or per-zone thermostatic controls, smart or otherwise, fix this. The smart version adds remote control and learning; the dumb version captures most of the benefit at a fraction of the cost.
Hot-water recirculation control. If you have a recirculation pump, putting it on a learning timer rather than running it continuously can dramatically cut its electricity and water-heating cost.
The smart things that don’t
- Smart bulbs in every room. Useful for scene-setting; not significantly more energy-efficient than non-smart dimmable LEDs. Each one draws standby power continuously
- Voice assistants. Real plug load, dubious sustainability benefit. Their environmental case rests on whether they reduce other behaviour (turning off lights, controlling thermostat), which they sometimes do and often don’t
- Smart appliances. Most “smart” features in fridges and washing machines are marketing layered on top of conventional efficiency. The efficiency rating on the label is what matters
- Smart blinds in every window. When motorised blinds genuinely close at peak sun and open in winter for solar gain, they save energy. Most installed motorised blinds end up parked in one position by occupants who find the automation unreliable
What I specify
In residential projects where a client asks for smart-home integration, I work backwards from the bill. Where is the energy actually going? Which controls can intercept it?
- Learning thermostat, zoned. Always
- Occupancy-and-daylight sensors on circulation lighting. Often
- Motorised blinds only on south-facing glazing where the orientation justifies them, and on a single automated routine the occupant won’t need to fight
- A hard switch by the front door that cuts all standby power in the bedroom and living room circuits when leaving the house
- Wired ethernet for the few devices that need it; minimum Wi-Fi mesh for the rest. Fewer networking devices, fewer continuous loads
Voice assistants, smart locks, smart cameras, smart kitchen gadgets — out of scope unless the client specifically asks. They’re convenience products, not sustainability products. Treat them as such.
The honest closer
A house is not made more sustainable by adding chips. It is made more sustainable by losing less heat, using less hot water, and turning off what isn’t in use. A small number of smart devices help with the third of those, modestly. The rest is the envelope and the mechanical system — the things that don’t have an app.