Hey Rick,
After my surgery, which was in mid June in Toronto, I was walking around in a woolen hat, and a warm jacket right through the summer months, which are quite warm there. It had nothing to do with Warfarin though. There is a common misconception that Warfarin is a 'blood thinner" first, and second, that 'thinned blood' will not keep you as warm.
My understanding (as a lay person, not a medical professional) is this. Warfarin is not at all a blood thinner, despite doctors, nurses, pharmacists calling it that sometimes. It acts to prevent the formation of clotting factors, which in turn increases the length of time required to form a clot (or more precisely, to form thrombin, which forms the clot). Aspirin, on the other hand, IS a blood thinner, in a sense, since it reduces the number of platelets in circulation, and platelets are a kind of 'unliquid' part of your blood.
So now, two and a half years post surgery, and gobbling 11mg of Warfarin every single day, I can tell you that I am LESS cold than before the surgery, and I credit that to improved circulation. Thank you new heart valve!