Space Heaters and Your Circuits: What 1,500 Watts Actually Does

Every winter we get the same call. A bedroom outlet stopped working, or a breaker keeps tripping, or — the bad version — the outlet is scorched. Somewhere in that room sits a 1,500-watt space heater, usually on an extension cord, on a circuit that also feeds a lamp, a TV, and three chargers. The heater almost always gets a pass in the story. It shouldn't. Here's the actual math.

What 1,500 watts actually draws

Watts divided by volts equals amps. A 1,500-watt heater on a standard 120-volt outlet pulls about 12.5 amps. A typical bedroom receptacle circuit is 15 amps.

That heater is consuming roughly 83% of the entire circuit by itself — before a single lamp, laptop, or phone charger is added. And a "bedroom circuit" in NYC is rarely just the bedroom. In a lot of pre-war apartments and brownstones, one 15-amp circuit was run to cover several rooms' worth of receptacles and lighting, because when that wiring went in almost nobody owned a 1,500-watt anything.

The real ceiling is 1,440 watts, not 1,800

15 amps × 120 volts = 1,800 watts, so on paper a 1,500W heater fits. In practice it doesn't.

The National Electrical Code — adopted with local amendments as the NYC Electrical Code — treats a load that runs three hours or more as a continuous load, and a branch circuit may only be loaded to 80% of its rating for continuous loads. On a 15-amp circuit that ceiling is 1,440 watts. A common 1,500-watt heater exceeds it on its own, with nothing else plugged in. The same 80% limit applies to cord-and-plug equipment that isn't fastened in place — exactly what a portable heater is.

The right home for a full-power portable heater is a 20-amp circuit (1,920 watts continuous) carrying essentially nothing else. Most NYC bedrooms don't have one. That's the whole problem in a sentence.

What the fire data actually says

Heating equipment is the second-leading cause of home fires in the United States, per the Electrical Safety Foundation International, and more home fires happen in winter than in any other season.

The U.S. Fire Administration's published numbers give the scale: about 27,900 residential building heating fires in 2023, causing 115 deaths, 525 injuries, and $488 million in losses.

The trend is genuinely good — across 2014–2023 the USFA recorded a 31% drop in heating fires and a 44% drop in deaths. Equipment got safer. The wiring behind the wall in a lot of NYC housing stock did not, and that's the part you can do something about.

A tripping breaker is the system working

This is the part people have backwards. When the breaker trips, the protection did its job: it saw more current than the wire behind your wall can carry indefinitely, and it opened. Nobody died. Resetting it once is fine. Resetting it every night is you overriding a warning.

These are the signs the system is failing, and every one means unplug the heater now:

1. A warm or hot cord or plug. Cords aren't supposed to get warm. Heat at the plug means a loose or degraded connection creating resistance — that's how a receptacle chars.
2. A warm faceplate or a discolored outlet. Same story, happening inside the wall box where you can't see it.
3. A heater on an extension cord or power strip. Most household cords and strips aren't built for a sustained 12.5-amp draw, and heater manufacturers' own instructions say to plug the unit directly into a wall receptacle. No exceptions, no "just for tonight."
4. A burning or hot-plastic smell, or lights that dim noticeably when the heater cycles on.
5. A breaker that won't stay reset. That's a fault, not simple overload, and it needs diagnosis by a licensed electrician.

Worth knowing at the store: the safety standard for portable electric room heaters is UL 1278, "Movable and Wall- or Ceiling-Hung Electric Room Heaters." A heater carrying a mark from a recognized testing lab — UL, ETL, CSA — has been tested against a real standard. An unlisted import off a marketplace listing has been tested to nothing. Look for the mark, and for a tip-over shutoff and an overheat cutoff.

The NYC layer

Under the city's Housing Maintenance Code, heat season runs October 1 through May 31: HPD requires at least 68°F indoors between 6 AM and 10 PM when it's below 55°F outside, and 62°F overnight. If you're running space heaters because the building isn't delivering heat, that's a complaint to HPD — not something to solve by stacking heaters onto century-old wiring.

If you own the building, the honest answer is often that the apartment doesn't have circuits sized for modern loads. The fix is capacity, not another heater: a panel upgrade and dedicated 20-amp circuits, filed with the DOB and inspected like all NYC electrical work. If you're moving off space heaters to heat pumps, New York State incentive programs can offset part of the cost of the electrical work — we handle those applications at apply.chazonelectric.com or by phone.

Look at it before it's cold

August is the right month for this, not January. If you already know which outlet the heater goes into every winter, have that circuit checked now — while the panel isn't loaded and nobody's cold. Chazon Electric is licensed and insured, working across all five boroughs. Call (718) 924-8062 and we'll tell you what that circuit can actually carry.