GarMan,I don't know how you guys in Canada do it! It's cold enough here in NYC!
On your question whether the 4 Pi needs a sub, the answer is "no", but a sub can be fun depending on what amplification you're using. I broke in my Pi 4s w/ a pp 40W EL34 amp (Assemblage ST40), which produced overwhelming bass. But after breakin I play my 4 Pis w/ 8W Welborne Laurels, which must roll off a bit at the bottom.
Even w/ the Welbornes, bass is fine, but I was spoiled by the fantastic bass I'd heard w/ the Assemblage. Because I'm obsessed w/ building speakers (and had never heard, much less owned, a sub), and because I had an unused Marchand crossover, I built a sub. The difference is subtle but fun and rewarding with Mahler and Eminem!