Hey Mitch
Your topic is really way out when it comes to Home Theatre.
Let me take a stab at it.
A large sub such as yours does move a bit of air but firstly, how close to the furnase is it? I would think a fan would be dangerous right next to the furnace but I don't think a sub can move any dangerous amounts of air.
If there is dust around, I would be concerned with the sub pounding dust off the floor and around the furnace with the airborne dust particles and clogging or suffucating the furnace with these particles. If I were you, I would call the local fire department and tell them your scenario. See what they say. For fire safety, they may pass by your house in one of their rounds. They do that service.
Give them a try just to be sure and worry free if you really want to put your sub by the furnace.
Hope this helps.
