When we built our house the basement was unfinished. We never added duct work for heating, figured we would use electric base boards. Jump forward 30 years, the basement is all finished, the duct work is accessible, could I put one register in to knock the chill off? I had a friend that did that and he says it works great. I have two BIL that are both in the building industry and they said do it. When we put our addition on I asked the A/C Heating guy if we could add a register and he had a fit. He said it would unbalance the system and cause all kinds of problems. I planned on letting the circulating fan run when the stove was in use, which is 24/7. All I can see is it would be circulating more air, so maybe more frequent filter changes. The heat pump would be off so there would be no extra load on the pump? When I say off, I don't mean turned off, it just never comes on while the stove is in use.