Unsurprisingly, this seems to be a matter of debate:

> In a 2014 interview in the Washington Post of University of Miami climatologist Larry Kalkstein, who has published numerous research papers on weather-related mortality, weighed in on the matter: “Comparing apples to apples, which would be to evaluate acute or short-term responses to weather, I would always give the nod to heat-related deaths. However, if you are considering the seasonal differences in daily mortality, rather than just the “spikes” that we find with acute deaths, I can see why one can argue that winter (or cold-related) mortality is greater.”

https://www.wunderground.com/cat6/Which-Kills-More-People-Ex...

Edit: I see we are citing the same article :)