For some reason toasty warm downstairs this morning (fire in woodstove) and cold upstairs. In past usually not this much difference though upstairs can get real chilly when it gets down in single digits. Had always kicked myself for not building in couple controllable ducts to get more heat upstairs. Figure its time. Simplest way would be to cut couple eight inch diameter round holes in floor and downstairs ceiling and slip in some 8" duct pipe. However I have never seen any round hot air floor registers. In forced hot air systems they always use those adapters to go from round duct to small rectangular register opening. Plus being this isnt forced air, would like max opening which would be round. Anybody ever see round hot air registers to put in floor? Ones that I can close if I want? I suppose I could cut and weld and make custom ones, but for effort involved, be easier to cut rectangular holes and custom bend rectangular ducts and use stock rectangular registers. Need more of them since modern forced air registers seem to be rather small..