So, I never see smoke coming out of my vent pipe, always see that "heat" coming out of it, but nothing billowing out or anything. Tonight we are at the coldest of the year(current about -9/-10 degrees. I took the dogs out a while ago and noticed I have large billows coming out. Not black or anything, but you can SEE the smoke. Is this normal for such a cold night, or something I should look at in terms of cleaning the pipe?