my bathroom has a 6" ducting. i have both the duct valve and the register closed. i would like to have a little heating in there, as much as what is leaking past now. but as it is now, because of such a low flow, i get cooler air. if i have a small duct, the duct would not cool the air, as the flow would be much faster through the smaller duct.
so, what is the smallest ducting avaliable ?