How to Size an Electric Baseboard Room Heater

Stay warm this winter.

Cadet 96" Electric Baseboard Heater


Project Overview
  • Total Time: 10 mins
  • Skill Level: Beginner

In a room where the existing furnace system is not sufficient to heat the area, or in a remodeled space where adding ductwork is not practical, the logical answer to staying warm may be to add electric baseboard heating. A remodeled basement, attic, or attached garage converted to living space may benefit from installing either 120-volt or 240-volt electric baseboard heating units. These units are a stand-alone solution that requires no additional ductwork or piping and can save a great deal of money over remodeling the existing heating system.

What to Know About Electric Baseboard Heating

Electric baseboard heating units come in many styles. Portable versions plug into standard 120-volt outlets and can be a good choice for rooms that will be used only sporadically. For ongoing use, you will likely want permanent (hard-wired) baseboard heaters that are wired directly into a household circuit. They are available in both 120-volt and 240-volt models (though 240 is more common and more energy-efficient) and in a variety of lengths, from 24 inches to 96 inches.

Most electric baseboard heaters work by electrical resistance—the heating element warms up as a natural reaction to electricity passing through it. There are also hydronic types, which work by heating up a self-contained reservoir filled with fluid. The fluid heats up metal fins, which radiate heat outward into the room.

The heat output of electric baseboard heaters is specified by wattage, which governs the amount of energy it consumes as well as its heat energy output. Watts are a unit for measuring electricity, and for any given baseboard, the output wattage will be governed by the size (length) of the heating unit and by the voltage of the unit. At the same length, a 240-volt baseboard heater produces (and consumes) twice the wattage of a 120-volt heater.

Solutions to Try First

Before going through the expense of buying an electric heater, you may want to try checking out these possible problems that prevent your furnace from effectively heating a cold room:

  • A heating register is closed or not fully open
  • A dirty furnace filter is reducing airflow
  • Heating ducts are dirty with debris
  • The warm air coming out of the heating register is blocked by furniture, draperies, or carpeting
  • The thermostat is located in an area where it gets warm quickly and thus shuts off before the room is adequately heated
  • The thermostat is not functioning properly or is improperly set or adjusted
  • Windows or doors are leaky or drafty
  • You have high ceilings that may require a reversible ceiling fan
  • The walls are poorly insulated

These are potential problems if your furnace can't "keep up" in a particular room. Remember that by fixing the underlying problem, you can enhance the energy efficiency of your home, even if you choose to install an electric baseboard heater.

What You'll Need

Equipment / Tools

  • Measuring tape
  • Calculator
  • Pen or pencil


  • Paper


As a rule of thumb, assume a room requires 10 watts of electric heating per square foot of room. In other words, a 10x10 room (100 square feet) will require 1,000 watts of electric baseboard heating. This heating can be provided by a single baseboard heater mounted on the wall. For larger rooms, the total wattage can be provided by two or more heaters.

  1. Figure Out the Square Footage

    Measure the length and width of the room in feet. Then multiply the length by the width to get the square footage. Write the measurements down in a notebook or on a scrap piece of paper.

  2. Figure Out the Wattage

    Multiply the square footage by 10 to give you the rough wattage of heating required for the room.

  3. Consider Adjustments

    Make adjustments to the heater size under some circumstances. For example, a room with two outside walls that are poorly insulated, or that include many windows, may require more baseboard heating. Similarly, a tall room with unheated space above it may require more heating. On the other hand, a small room with only interior walls may get by with a smaller baseboard heater.

  4. Choose Your Heater

    Choose one or more baseboard heaters that total or slightly exceed the required wattage calculation. Match the wattage as closely as possible to the amount the room requires. Oversizing or under-sizing the heater will result in wasted energy and possibly affect the lifespan of the unit. The wattage information is specified on the heater packaging and labeling. Typically, a 1,500 watt/240-volt unit can heat a 150 to 175 square-foot room.