Resistive and strip heat: the easiest thing to control

Typical connected load

Resistive heating covers a wide family: electric baseboard, wall heaters, unit heaters, cove heaters, toe-kick heaters, duct-mounted strip heat, and the auxiliary elements inside heat pumps and air handlers.

Individually they are modest. Electric baseboard runs about 250 watts per linear foot, so an 8-foot section is roughly 2 kW. A wall heater is 1.5 to 4 kW. A garage or warehouse unit heater is 5 to 15 kW. Duct strip heat is banked in 5 kW increments.

Collectively they add up fast. A house heated entirely with baseboard can easily carry 20 to 30 kW of connected resistive load spread across a dozen rooms with a dozen independent thermostats.

Why it spikes demand

Independent thermostats that all respond to the same weather. Every baseboard heater in the house makes its own decision, but they all make it based on the same outdoor temperature, so they make it at roughly the same time. Cold snap arrives, every room calls for heat, and twelve separate 2 kW loads become 24 kW on your service in a matter of minutes.

Nobody planned it. No individual heater is doing anything wrong. But the sum is your monthly peak.

This is also the load type most likely to be invisible to the occupant. Nobody watches a baseboard heater. There is no sound and no visible cycle. Most people have no idea how much of their bill it accounts for until they see the interval data.

Thermal storage and deferrability

The heaters themselves store very little. A baseboard element cools within a minute or two, though the metal fins hold a small residual.

The room stores more, and that is what makes deferral work. Cutting a 2 kW baseboard heater for eight minutes changes room temperature by a fraction of a degree in most construction. Cutting three of the twelve heaters for eight minutes, then rotating to a different three, holds total demand flat while every room stays essentially at setpoint.

Rotation is the key concept. You are not turning off heat. You are running nine out of twelve at any given moment and changing which nine.

What an interruption feels like

In a rotating configuration, nothing detectable. Rooms hold within a degree.

In an aggressive configuration during genuinely cold weather, a slow drift in the rooms that are currently deferred, recovering when they cycle back. It behaves like a slightly less responsive thermostat.

The failure case worth naming: a single room with poor insulation, a north exposure and a lot of glass will drift faster than the rest of the house. If someone works in that room all day, it should be excluded from control or given a higher priority.

Where it sits in the priority order

Below air conditioning, above water heating, in the general electric heat band. In buildings where resistive heat is the dominant load, it gets subdivided across multiple control points so it can rotate rather than shed as one block.

Resistive loads get no minimum on-time and no minimum off-time. This is worth stating plainly because it is a real advantage. Air conditioning needs a minimum 8 or 10 minute run and a 5 minute rest to protect the compressor. Resistance heat needs neither. There is no motor, no refrigerant, no mechanical wear from rapid switching. Bill Brayden's guidance is direct: put no restrictions on the demand control algorithm for resistive loads. The more freedom the algorithm has, the flatter it can hold the curve.

The honest caveat

Resistive heat is easy to control and expensive to run, and demand control does not change the second part. You are still paying full price for every kWh. If you are heating a whole house with baseboard in a cold climate, demand control will reduce your demand charge and leave your energy charge where it was.

Also, controlling a dozen distributed baseboard heaters means getting a switching device to each one. In existing buildings that is usually done with power line carrier receivers mounted at the load rather than running new control wire, which keeps it practical. But it is more hardware and more labor than controlling one water heater, and the proposal will reflect that.

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