I'm not in the heating business, but I've had some work-related experience with ventilation.

As you heat air the capacity for moisture retention (humidity) increaces. Windows are normally the coolest spot in a room. When the warm moist air reaches the cool windows condensation occurs. The best way to solve this problem is to add heat to the window area. One way to add heat is to install an electric heat panel under each window. The heat will rise and keep the windows from fogging. Another way, if you live in a moderate climate, would be to install a celing fan. The fan would increase the warm air flow outward causing the windows to warm up, thus minimizing the condensation.

From what I've been able to accertain from my research is that venting a heating source is always desireable.

TGG