“This little, super-efficient electric heater ONLY uses 1525 watts of electricity, yet puts out a whopping 5200 Btus of heat!!!”  What is wrong in this statement? A couple of things.

One is just my pet peeve, confusing units of power and units of energy. It should read “5200 Btu per hour.” The ”watt” is a measure of power, or the rate at which you use energy, while the “Btu” is an amount of energy. It’s like the difference between speed and distance. If the Btu is the “distance” the watt is the “speed.” (Imagine you asked a car salesman how fast this car could go, and he told you it would go 600 km on a tank of gas.) But, it turns out that in the heating trade,  “Btu per hour,” is often shortened to just “Btu,” so okay.

But: The second flaw in the statement is a deception. 1525 watts is equal to 5200 Btu/hour. 1525 W is the rate at which the heater uses electrical energy, and 5200 Btu/hour is the rate at which it puts out thermal energy. They are the exact same amount, just in different units. It’s like saying, “Wow, I only put one gallon of water into this bucket, but got 4 quarts out of it!!” It’s just that in the electricity world the preferred power unit is the watt, while in heating, in the U.S. it is the Btu/hour.

So as this indicates, all of the electrical energy going into the heater comes out as heat. All electric heaters have an efficiency of 100% (i.e., no energy is lost or spilled). In fact, most electrical appliances have an efficiency of 100%—as electric heaters. That includes light bulbs, televisions, and even refrigerators. All their energy ends up as heat. A refrigerator that uses 350 watts of electricity when it is running puts out 350 watts (1200 Btu per hour) of heat.

Even though electric heaters are technically 100% efficient, you can actually do better–More on that later. First a review of some electric resistance heater options.

There are three common types of electric heaters that can serve different purposes. Most common are convection heaters. They contain a heating element (disc or coils) and a fan that blows air over the element. The warm air then circulates around the room, warming it up.

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The second type looks like a small radiator and is filled with some oil that is heated by an internal heating element. It works by natural convection like a normal radiator.  These two types of heaters are good for temporary or supplemental heat in a small space.

The third common type is the radiant, or “infrared” heater. Rather than heating the air, the radiant heater sends most of its energy to objects directly in front of it. These are effective for warming anything directly next to them in more open spaces. Think campfire.

Prices vary widely on these heaters, sometimes on the exact same heater with a different label. There are important differences between some of the very inexpensive ones and the mid-range heaters, but these differences usually have to do with safety. A good heater should have a “tip-over” switch.  The heaters with ceramic disk elements are considered a bit safer than the coil heaters because the surfaces are not as hot. But overall, the point is–energy in, energy out: you can’t do better than 100%. Except, with resistance heating, 100% isn’t entirely what it seems to be.

First of all, that 100% is only the last step in the series of steps it takes to get the electricity to your home.  In each step there is some loss: At the power plant electricity is produced with around 40% efficiency from natural gas. Then there are losses along the way with gas delivery and transmission of electricity. In the end, only about 30% or so of the original natural gas energy ends up as electric heat in the home.

A better-than-100% way of electric heating is a heat pump.  Heat pumps use electrical energy to leverage heat out of cold ground or air. The net effect is that you get much more heat into the home—typically three to six times as much—from the same amount of electrical energy. That means the heat pump is three to six times more efficient than the electric heater, and that much less costly to run.

So, when does it make sense to have an electric heater?  First, they are very handy and usually inexpensive to buy. If you have a small space that requires occasional heat the electric heater can be a sensible choice. For long-term heating of larger spaces, the extra cost of a heat pump is easily compensated for by the reduced operating cost.

Just keep in mind that when you buy a 1500 watt electric heater, whether you pay $150 for a fancy “portable-quartz-tube-electromagnetic-space-heater” or $15 for a simple convection heater, whatever wild claims the ads may make you will be getting 5120 Btu per hour into the space. They are all 100% efficient, and they are all less than one-third the efficiency of a heat pump!

Paul Stancioff, PhD., is professor emeritus of physics at UMF. Cynthia Stancioff re-words everything he writes. Email: [email protected] or [email protected]. Previous columns can be found at https ://paulandcynthiaenergymatters.blogspot.com/.

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