A city with 50,000 compromised heaters drawing 1.5KW lets an attacker play with 75MW on the electric grid. (I just picked the middle value in a list of heaters;

A city with 50,000 compromised heaters drawing 1.5KW lets an attacker play with 75MW on the electric grid. (I just picked the middle value in a list of heaters; probably not a good estimate.) A moderate county (roughly 2 million people in 800,000 households) has about a 2400MW power supply. Compromising 6% of households' heaters would allow you to drive spikes on the order of 3% of the average power grid load (which includes things like business uses). With some targeting, you could probably get a larger influence on a localized portion of the grid. Somehow, I think attackers causing high-ish frequency noise (on the order of ~1 minute waves, or less) with 3% of the average power could cause problems for the electric grid.