YOu already have the correct idea.

The light will heat the grow environment but you need to balance it with your exhaust. You need ideally a variable speed control to audit the air in and air out.

Place a thermometer in room or chamber and check it every 10 minutes quickly.

KEEP ACCURATE records...you will learn that when it is X degrees outside, your inside grow area will be Y degrees. You can then determine the heat put off by your lamps and adjust the air exhaust 'Z' accordingly...
HARDDON Reviewed by HARDDON on . cold weather indoor ventilation? BUDBOX Was wondering if anybody had any advice for someone growing in an UNHEATED but insulated building in the cold of winter wth regards to ventilation. Were talking cold--high in the mountains cold--and probably only want to ventilate enough to get rid of stale air. Specifics: BUDBOX or similar (3ftx3x6ft) portable tent. 400w mh/hps depending on stage (no veg room yet) CO2 enrichment to be used. exhaust/inline fan???????????????????? was thinking about using a normal inline Rating: 5