Pretty bad.
Heat is "low quality" energy. Electricity is "high quality" energy generated from heat with a considerable conversion loss. Conversion back into heat is fairly efficient, but you've already paid the cost.
Here in California, back in the late 50s and very early 60s, communities of "Medallion Homes" were being built with great ballyhoo from the electric companies. All electric, no gas. "This is the future!" Nuclear plants were supposed to produce electricity "too cheap to meter", remember, and a lot of people suckered for this.
Later they found it nearly impossible to sell these Medallion Homes because the heating costs were horrifying, even here in Southern California.
