Space Heater vs. Furnace

2 minute read

space heater

A recent article by CNET alleges that you can save hundreds of dollars of heating a year by lowering your overall thermostat and running a space heater in target rooms.

In this post, we’ll walk through the specific math, and give you a calculator to estimate if this strategy might make sense for you. We’ll also compute the carbon-related costs and benefits of this strategy. We focus on electric space heaters, which are less efficient but more safe than combustion space heaters1

Energy Costs of Operating a Space Heater

The amount of energy, and cost, required to heat a space with a space heater is a function of the size of the space, insulation of the space, and your electricity pricing.

A typical space heater is rated for 1,500 Watts2, so running one overnight in a small bedroom overnight (10 hours) would come to 15,000 Watt hours or 15 kWh. The below chart shows example per-kWh pricing for major US cities. Converting the electricity values to heat, 1,500 kWh outputs is equivalent to 5,118 BTUs, or .05 Therms3.

Using, say 22 cents per kWh, a ten hour overnight run of a space heater would be $3.30. Using a multi-family house in a northern climate as an example, overnight heating is estimated to utilize between 1.5 and 2 therms, or 150,000 to 200,000 BTU, for whole house heating overnight. While this is an order of magnitude more energy than the space heater’s .05 therms, the US average price per therm of $0.954 means that this overnight heating is only costs $1.5 to $2, or less than the space heater. For individuals with higher gas prices, or using a fuel like propane or heating oil, this strategy might make more sense.


It’s important to note that, for most households, space heaters are an inefficient method of heating and a more sensible step, especially for overnight heating, is to utilize multi-zone heating to heat only a bedroom. If the thermostat is close to your bedroom, close other doors and vents to keep the heat near the bedroom area.

Even better, a heat pump can use the same amount of electricity to produce several times the heat of a space heater, and can either be installed into your central ductwork, or as mini-splits to produce zone-based heating.

If you’re worrying about gas bills from heating, please contact us for a customized decarbonization plan


  1. US Energy Department: Space Heaters