Heat Troubles - Small Setup

Hello

I have a 1x1x2m mylar tent, 250 W Bulb/ballast and Inline fan drawing through a carbon filter venting to the outside room. I purchased a fan control (cranked it way down) because the fan was too powerful and I had low temp problems. During dry runs was able to get the temp to around 22 degrees (71F) fairly quickly (ambient temp outside is 15C). Currently the ballast is outside the tent, there is plenty of space for it on the inside of the tent where it could contribute to the temperature (the ballast doesn't get crazy hot because its such low watt). Does anyone else run their ballast inside the tent for temp purposes? Is that okay? How much of an increase should I expect? Will it blow out due to humidity?
FYI this is a 2-3 plant max tent for me.


Ambient temperatures for night cycle are down around 15C (60 F).

it might seem like a good idea to use the ballast for heat but you dont want that to be anywhere near any potential water exposure from watering and/or spills. 15C is a bit cool for veg room so if you kept the exhaust fan off for a few hours a day perhaps the temp could stay a bit higher, also they sell tiny space heaters for like 10 bucks at walmart. I had issues with my room and bought one of those and was the easiest solution to such an annoying yet crucial element.

How is the cost of running the space heater? Do you run it on a timer for when the lights are off or set it on a temperature trigger?
I was just going to increase the ambient temperature to around 16C I have read that 15C+ is okay for night and 21C + is fine for light (when not using CO2).