What i am wondering is how much time to run the exhaust fan, see here we have really bad winters and my grow room is closed off and it stays at decent temps (67F) with the heat from the light, but the temp outside the grow room is ridiculous cold (55F) and lower. Now i tried to run my exaust fan 24,7 since my light is on 24,7 but my temperatures started to fall way too much and humidity drop alot also from 67F, 65%RH to like 60F , 45% RH. now i am looking to buy small heater with ajustable thermostat but i would like to keep the heat in the grow room as much as possible, but i do understand that fresh air is needed but would 5 mins every hour so or something resonable?