Im setup to switch to 18/6 tonight. Right now I am using a red bulb heat lamp. It keeps temps between 76-78. I have it plugged in to an inkbird controller to shut off at 78. Temps and rh have been great since I switched to the heat lamp from a space heater but now that the lamp will be off for 6 hours I think im going to run into a problem. I expect there to be a 15 degree drop during lights off. I really dont want to go back to the space heater.
Also, I fired up my intake and exhaust today. Im drawing air from the warmest area of the house I can get to which is around 69 degrees. When I turn the fans on it really brings down temps and I lose all my rh. Id really like to get some air circulating for the plants and to keep the smell down a little. I guess I might have to except its what I have to deal with.
I always have at least a 15 F drop in temperature when lights are off. I have never seen a problem even when the lights off temperature gets to the low 60’s.
Well that makes me feel much better because 61-62 is likely where it will be! I could probably keep temps a little warmer running my fans at night but id loose all my rh
I run my lights on temperature between 77 F and 84 F. I don’t really worry about the lights off temperature. I keep the rH below 70%. rH does get very low in the winter months. It is not ideal but I have not seen any problems.
You inline fans exchange the air for the plants to breath , they will adapt if you keep it stabilize , 58 ° - 82° they will still veg and grow just slow if the temps are low . They usually create they own humidity if they drinking water daily ?
@yoshi if I keep my intake and exhaust fans on it will pull temps down to 66-68 and cut my rh in half to around 30. They are definitely drinking water but here in my area its just a tough time of year to make heat and humidity.
Since going to veg ive been keeping fans off with lights on and turning them on at lights out
Let me see the plants 
, they will tell me more they you can !
I am switching to RO from here on out. System will be here Monday
I grow exclusively outdoors and I have kushes that in September and October see 70° daytime and 40s at night. In October I have had my plants see 30s and they only have benefited from it. Now if they are baby seedlings I would keep the temps warmer, but once established they are totally fine 
My wife keeps reminding me of what they deal with outdoors and I need to stop worrying so much.
Right now the plan is for two of these to go out doors near the end of veg indoors. Hopefully they become monsters.
Cannibas plants are very strong plant you will be just fine I’ve had it get down to 45 degrees in appalachian mountains in summer time happy growing @Khaos850
So now the question is if its better to have cooler temps and rh with circulating air or warmer temps and higher rh with fans off?
They will tell you but it you dont stabilize one or the other you will turn them hermie !
Definitely dont want that. Just turned fans on to circulate as I’ve made up my mind fresh air for them is more important to me. Thanks
Smart choice !
It will be a little cooler and less rh but at least no fluctuation now.
I tapped into an overhead heating duct in my basement for supplemental heat. This worked very well to add about 10 F to a 65 degree tent BEFORE light shut off.
Are you losing heat because most of your heat is supplied by the light and not the red bulb?
Maybe consider switching to a reptile lamp & ceramic bulb if you want to keep the temp up.
I have my fan pulling fresh air in all the time, about 68F & my light & bulb keep the canopy at 78F. When the light is off, the bulb does all the work.