Reference
Heating element glossary
The terms that turn up on rating plates, in manuals and in quotes, explained without assuming you already know them.
- Auxiliary heat
- Electric heating elements that switch on automatically to supplement a heat pump when the outdoor temperature drops below the point at which the heat pump alone can carry the load. In Ontario this typically means the coldest stretches of winter. Distinct from emergency heat, which is a manual mode.
- Balance point
- The outdoor temperature at which a heat pump's output exactly matches the building's heat loss. Below this point auxiliary heat is needed to hold temperature. A wrongly set balance point is a common reason for unexpectedly high winter hydro bills.
- Bolt-in element
- A water heater element held against a gasket by a four-bolt flange rather than threaded into the tank. Found on older residential and many commercial tanks. Not interchangeable with screw-in elements.
- Cone
- A measure of heat work in ceramics, combining temperature and time rather than temperature alone. Cone 6 and cone 10 are common firing targets. Higher cone numbers mean more heat work and shorter kiln element life.
- Continuity
- An unbroken electrical path through a component. Testing an element for continuity with a multimeter shows whether the resistance wire inside is intact. No continuity means the element has burned open and must be replaced.
- Dry fire
- Energising a water heater element that is not submerged in water. A copper element can be destroyed within seconds this way. It is the most common cause of an element failing immediately after a tank has been drained and refilled for service.
- Emergency heat
- A manual thermostat mode that locks out the heat pump compressor and heats using electric strip elements alone. Useful for testing strips, and as a fallback when the heat pump itself has failed. Considerably more expensive to run than normal heat pump operation.
- Element holder
- A hard ceramic channel that supports a kiln element rather than letting it sit in a bare brick groove. Holders protect the brick from glaze drips and generally extend element life. L&L kilns are the best-known example.
- Heat kit
- The assembly of electric heating elements, sequencers and safety controls fitted into an air handler or electric furnace. Usually rated in kilowatts and identified by its own label, separate from the air handler's rating plate.
- Heat strip
- An electric resistance heating element used in air handlers, electric furnaces and heat pump systems. Often arranged in multiple stages that energise in sequence rather than all at once.
- Incoloy
- A nickel-iron-chromium alloy used for heating element sheaths. More resistant to scale, corrosion and brief dry-fire events than copper, and generally the better choice in hard-water areas.
- Kanthal
- An iron-chromium-aluminium alloy used for kiln element wire. Kanthal A-1 is the most widely used grade in electric pottery kilns. It forms a protective oxide layer at high temperature, which is why kiln elements should not be fired in a strongly reducing atmosphere.
- Limit switch
- A safety control that cuts power to heating elements when cabinet temperature exceeds a safe threshold, usually because airflow has been restricted. Repeated limit trips are a warning that something is wrong with airflow, not with the switch.
- NPT
- National Pipe Thread, the tapered thread standard used for screw-in water heater elements. Residential screw-in elements are almost universally 1-inch NPT.
- Ohm
- The unit of electrical resistance. Measuring resistance across a heating element's terminals is the standard test for whether it has failed. A 240V 4500W element reads roughly 10 to 14 ohms when healthy; an open reading means it has burned through.
- Open circuit
- A break in the electrical path. On a multimeter set to resistance, an open circuit reads as infinite or out of range, commonly shown as OL. On a heating element it means the resistance wire has burned through.
- Rating plate
- The manufacturer's label carrying model number, serial number, voltage, wattage and other electrical data. It is the single most useful thing to photograph when requesting a replacement element.
- Screw-in element
- A water heater element that threads directly into a 1-inch NPT boss in the tank wall, sealed by a gasket. The most common arrangement on modern residential electric tanks.
- Sediment
- Mineral scale that settles at the bottom of a water heater tank. It buries the lower element, forces it to work harder against an insulating layer, and is the leading cause of repeat lower-element failure in hard-water areas.
- Sequencer
- A timing relay that brings electric heat stages on one at a time, a few seconds apart, so the system does not draw its full current in a single inrush. A failed sequencer often imitates a failed element, which is why testing matters before ordering.
- Sheath
- The outer metal tube of a heating element, which separates the resistance wire from the water or air being heated. Common materials are copper, Incoloy and titanium, each suited to different water chemistry and duty.
- Three phase
- An electrical supply arrangement common in commercial and industrial buildings, typically 208V, 480V or 600V in Canada. Three-phase heating elements are not interchangeable with single-phase equivalents.
- Thermal cycling
- Repeated heating and cooling of a component. Elements that sit idle then run hard, such as heat pump auxiliary strips, see more thermal cycling stress than elements in steady duty, and tend to fail at terminals rather than mid-coil.
- Wattage
- The power an element consumes, and therefore the heat it produces. A replacement element must match the original wattage — fitting a higher-wattage element overloads circuits that were never sized for it.
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