You don't mention specifically, but assume you're taking advantage of this feature of your tent, cited in Columbia's product description:

Cyclone Venting System Keep warmer or cooler- it's up to you, not the temperature outside. The venting system creates a vortex that flushes hot air up though the roof, providing fresh air all night long. For maximum climate control, open or close the lower vents to feel the cool night breeze or keep warm air in.

Or, have you thought about approaching the problem by warming your bags, rather than the whole tent, using something like this or similar products like this?

Then, there's always electric socks, but my wife says she'd freeze to death before she'd wear those <img src="/images/graemlins/grin.gif" alt="" />