Recycling heat from light fixtures.

Being a UK owner, I need additional heat for my vivariums. Last winter I strapped 2 heatmats to each one (back and side), each controlled by a Habistat thermostat - this method only raised the temps a few degrees above ambient though.

This winter i'd like to use a more effective method, as the vivariums are only sitting at an average of 69F in the day - what about using the waste heat from the light fixtures? After measuring the temperatures - the air below the LEDs sits at 78 F. What about placing an 80mm fan above each tank, and blowing the warm air in through the vents (controlled by a thermostat of course)? My only concern is the air being pushed in causing a humidity drop (although I could just increase the MistKings misting frequency to counteract this)

Thoughts?

Regards

Anthony