Questioning Space Heater Efficiency

We recently received a comment from a reader about a 2016 article on electric space heater efficiency (“Electric Space Heaters,” January 2016, page 30). The article included this stat: “Electric space heaters are all 100 percent efficient at turning electricity into heat, but an Energy Star air-source heat pump can be 300 percent efficient.”

Q: It’s nearly impossible to have a 100 percent efficient heater. In reality, most heaters are around 30–50 percent efficient. To list a 300 percent efficient heater shows that you don’t have someone on your staff who understands what heaters actually do. A 300 percent efficient heater breaks the first law of thermodynamics.

Shawn, submitted via carolinacountry.com

A: You make a good point, Shawn. The first law of thermodynamics states that energy cannot be created or destroyed. The “300 percent” figure used in the article was imprecise. What it means is that a heat pump can deliver about three times as much thermal energy as it uses in electric energy. The heat pump does this by capturing heat in one location and delivering it to another location. Instead of converting electric energy to thermal energy as an electric resistance heater does, the heat pump is primarily moving heat from place to place.  

Thank you for a good comment — it tells me I need to be more clear when I talk about heat pump efficiency.