Clothes dryers: the load we protect

Typical connected load

A residential electric dryer heating element draws 5 to 6 kW. The drum motor and controls run on 120V and draw a few hundred watts. Total nameplate is usually stated around 5.6 kW.

Commercial and multifamily laundry equipment runs larger, and in a shared laundry room there may be six, ten or twenty machines on the same service. That is a different problem entirely, and it is one of the strongest commercial demand-control cases there is.

Why it spikes demand

Two reasons, and the second one is more interesting than the first.

The obvious reason is size. Five to six kilowatts landing on your service in one step is a large step, comparable to a full-size air conditioner.

The less obvious reason is that dryers are user-initiated at unpredictable times. Your water heater and your air conditioner run on physics. Your dryer runs because somebody decided to do laundry, which is very often Saturday afternoon or right after work on a weekday, and right after work is directly inside the on-peak window on most demand plans.

There is one thing working in your favor. A dryer's heating element does not run continuously. It cycles on and off every few minutes as the thermostat regulates drum temperature, so the average demand contribution across a full billing interval is roughly half the nameplate. A 5.6 kW dryer contributes something closer to 2.5 to 3 kW to a 30-minute interval average. That is real, and it is one reason a dryer is less damaging to your peak than its nameplate suggests.

Thermal storage and deferrability

None, and none.

There is no thermal storage in a clothes dryer. The drum holds a small amount of heat that dissipates in under a minute. And unlike every other load on this list, the dryer has a human being attached to it. Somebody put clothes in it, pressed start, and expects them to be dry when they come back.

This is the single least deferrable load in a home.

What an interruption feels like

Bad. Which is exactly why the system is configured not to do it.

If you interrupt the heating element, the drum keeps turning, air keeps moving, and nothing gets dry. A one-hour cycle becomes a ninety-minute cycle and the user notices immediately. Worse, they often notice without knowing why, which turns into a support call and a customer who no longer trusts the system.

Where it sits in the priority order

Priority 1. The highest priority in the system. Last load shed, first load restored.

This is deliberate and it is one of the clearest design decisions in the product. The dryer's heating element wires to the K1 relay on a standard residential installation and gets the top priority slot. Every other controlled load in the house gets held before the dryer does. In practice, on most homes, the dryer never gets held at all, because there is enough headroom in the water heater and the air conditioners to solve the problem before the algorithm ever reaches priority 1.

Note also that only the 240V heating element goes through the relay. The 120V drum motor stays on utility power untouched, so the drum keeps turning and the load keeps tumbling regardless.

The honest caveat

Two of them.

First, some modern dryers with electronic controls will not operate at all with one phase interrupted, because the control board watches for both legs. On those machines the installer has to control the full 240V circuit through the relay, which means an interruption stops everything including the drum. That changes the calculus and it is worth knowing before installation. It is a machine-by-machine question.

Second, the dryer's protected status means it is not contributing much to your savings. If your peak problem is genuinely a laundry problem, and in some multifamily and senior-living buildings it is, then the answer is different: control the machines as a group with rotation, not individually with a top priority. That is a commercial configuration, not a residential one.

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