We recently bought a 100-year-old house. I would like to put the Christmas tree in the entry way. There is a large return vent in the floor and the tree skirt will cover half of it. There are 2 other vents in the floor in other rooms on the main level, so it is not the only one.
Will it be a problem if it is partially covered for 3 weeks?
Thank you

Is this a return air vent or a vent that the warm air comes out of? If it is a return air duct it would not hurt anything for it to be covered during the Christmas season.
If it is a warm air duct there is always a chance something unforseen could happen. Like melted plastic, the heat weakening the electric wire. Like I said these are unlikely but just remember Murphey's Law.

The two other vents you spoke about,, are they supply or return? If the one you are needing to cover is the only return,, I wouldn`t cover it if it was my house,, cutting off or back on return means less supply coming out and could cause furnace problems