Our home has two furnaces (oil fired hot air) and an electric water heater in an enclosed room (approx 6'6" x 9'). Three walls of the room divide it from the remainder of a finished basement, the fourth is an outside wall that includes a vent for combustion air intake.
In cold weather, especially when both furnaces run frequently, the room becomes quite warm -- into the 90s (F) at times. I'd like to be able to divert some of this heat into the house without leaving the door open (which is quite effective, but inconvenient, as it opens into a spot that we often walk through). I've already sealed as many air leaks in the ductwork as I can find (a total of four zones are served by the two furnaces, so there is a lot of sheet metal in there), I think a lot of remaining heat is being radiated from the furnaces themselves and the flue pipes (they are single-walled until they exit the room).
I'm thinking of putting a pair of vents -- one high, with a thermostatic fan to blow the warm air into the room, and a low one, to balance the airflow -- in the wall shared with the office. Outside of heating season, the vents could be closed to prevent outside air (from the combustion air intake vents) from circulating into the office.
The only specific risk I can see would be the risk of CO being pulled into the room if there is a furnace failure. We have working CO detectors in the house, and I suspect it would be circulated throughout the house anyway due to leaks in the return ducts (around the filters, for example), so I'm not sure if this adds risk or not. I know that furnaces in many homes I've seen are not in enclosed rooms, so perhaps I'm overthinking this.