Parts of a Baseboard Heater – Labeled Diagram

All 10 parts on the diagram

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Case 3

Front cover It comes off to reach the element and the wiring. Air passes under its bottom edge and out over its top.
Cabinet (housing) The element and its fins run the length of the cabinet.
End caps On some heaters one slides off. That opens the wiring compartment behind it.

Heating parts 3

Fins They are usually aluminum. They give the element far more surface to pass its heat to the air.
Heating element The electric element is sealed inside a metal pipe, called the sheath.
Copper tube It takes the place of the electric element. Hot water from a boiler runs through it and heats the fins.

Wiring and controls 4

Wiring compartment There is one at each end. The supply wires can then come in at either end. Some makers call it the junction box.
Knockouts One is knocked out to bring supply wires into the wiring compartment.
High-limit switch Its long sensor runs the length of the heater. Makers also call it the limit control.
Thermostat Some heaters have one built in at the end, with a knob. Others are run by a thermostat on the wall.

How this list was compiled: Every name checked on 2026-09-30, a name kept only where two independent sources use it or describe the part: the US Department of Energy's Energy Saver page on electric resistance heating (https://www.energy.gov/energysaver/electric-resistance-heating, read from the Internet Archive copy); three heater makers' instructions for electric baseboard heaters (https://archive.org/details/manualzilla-id-6166319, https://archive.org/details/manualzilla-id-7318944, https://archive.org/details/manualzilla-id-7378899); a boiler maker's instructions for a hydronic baseboard (https://archive.org/details/manualzilla-id-6958218); and Wikipedia, Radiator (heating). No maker is named on the page. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; a schematic of no maker's product, nothing traced. Licence: own work

How it works

A baseboard heater is a long, low heater along the bottom of a wall. The drawing shows an electric one with its front cover lifted off, then a hot-water baseboard.

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How it heats a room

The heating element runs the length of the cabinet through a row of fins. Cool air near the floor is drawn in at the bottom, is warmed as it passes between the fins, and rises into the room from the top. A thermostat switches the heater on and off, and the high-limit switch turns it off if it overheats. A hot-water baseboard works the same way with a copper tube of hot water in place of the electric element.

The wiring compartment and the thermostat can sit at either end; the drawing shows one of each.
Baseboard heaters are usually put under windows, where the rising warm air meets the cool air falling from the glass.

Questions and answers

What are the parts of an electric baseboard heater?

A cabinet with a front cover and two end caps; inside it a heating element running through a row of fins; a high-limit switch; a wiring compartment at the end; and a thermostat, either built into the heater or on the wall.

What does the high-limit switch do on a baseboard heater?

It is a safety control. If the heater is blocked or overheats for any other reason, it turns the heater off automatically. Its sensor runs the length of the heater.

What are the fins in a baseboard heater for?

They pass the heat to the air. The element alone has little surface; the row of aluminum fins round it gives the air much more hot metal to pass over on its way up through the heater.

What is the difference between electric and hydronic baseboard heaters?

What heats the fins. An electric baseboard has an electric heating element inside a metal pipe. A hydronic, or hot-water, baseboard has a copper tube with hot water from a boiler running through it.