Smart plug and space heater: is it safe?

Why a heater is the hardest load for a smart plug

Most devices on a smart plug draw a few watts to a few hundred. A common space heater draws 1,500 W, the most a standard 120 V household plug is meant to deliver, and it does so for hours. At 120 V, 1,500 W is 12.5 amps (watts ÷ volts). A smart plug has a relay and thin internal conductors in a small plastic body. Heat builds up at the contacts, and a plug rated 15 A is being asked for 83% of its limit, continuously, in a corner behind furniture.

Fire agencies treat this combination as a hazard. The U.S. Fire Administration reports that portable heaters were involved in 3% of residential heating fires in 2017–2019, but 41% of the fatal ones. Its safety graphic tells people to plug heaters directly into wall outlets and not into an extension cord or power strip. ESFI gives the same advice, and says to keep heaters at least 3 feet from anything that can burn. A smart plug adds one more connector between the wall and the heater, and manuals that ban power strips usually mean it.

Check three things before you consider it

1. The heater manual. Look for the words “plug directly into a wall outlet” or a ban on extension cords, power strips and “timers”. Many manuals say so. If yours does, the answer is no, and using a plug anyway can void the warranty.
2. The smart plug’s rating. The label must list at least 15 A and 1,800 W, and it should say it can carry heating or resistive loads. A plug marked 10 A or 12 A is not suitable. A rating alone does not make it a good match for continuous heat.
3. The outlet and cord. Plug the heater in directly for 30 minutes and then feel the plug and the wall plate. Warm is a warning, and a hot or discolored plug means stop using that outlet and call a licensed electrician.

How much of a plug’s limit a heater uses

The lower settings leave more margin, but the other half of the problem is time. A heater that cycles on and off for eight hours puts more wear on a relay than a lamp ever will. You can price the heater’s running cost with the space heater cost calculator.

Safer ways to get a smart heater

• A heater with the controls built in. Look for a thermostat, a programmable timer or an app, tip-over shutoff and overheat protection. The timer lives inside the product, so the manufacturer has designed the switching hardware for the load.
• A line-voltage smart thermostat for fixed electric heat. Baseboard and wall heaters on 120 V or 240 V circuits need a thermostat that switches the load directly. Check the amp rating against the heater, turn the power off at the breaker and hire a licensed electrician if you are unsure. See smart thermostats for baseboard heat.
• A heat pump or mini-split. The Department of Energy says a modern heat pump can cut heating electricity by up to 75% compared with electric resistance heat. A mini-split can be made smart with an adapter; see smart control for mini-splits.
• Zone the central system. If you only want one cold room warmer, a remote room sensor on a smart thermostat often solves it without a second heat source.

If you automate anyway: rules that reduce risk

• Use an automation that turns the heater off (a schedule, a timer, no motion for 30 minutes) rather than one that turns it on while you are away. The USFA advises turning heaters off when you leave the room or go to bed.
• Never use a smart plug on a heater that has no tip-over shutoff, or in a bathroom, a child’s room or a room with a pet that could knock it over.
• Keep the plug visible. Do not run it behind a bed, a curtain or a bookshelf.
• Add a smoke alarm and a carbon monoxide alarm on that level. See wireless interconnected smoke alarms.

What else not to put on a smart plug

• Other heat-producing appliances: toasters, hair dryers, irons, portable oil-filled radiators and electric blankets with their own controllers.
• 240 V appliances such as dryers, ovens and window air conditioners that run on 240 V. A 120 V smart plug does not fit them and must never be adapted.
• Medical equipment and anything that must not lose power.
• Anything on an extension cord or power strip that already carries other loads.

Smart plugs are well suited to lamps, fans, humidifiers and electronics. For measuring what a device draws, see smart plugs with energy monitoring.