I really really don’t think you need a space heater. Put wire shelving in the bottom to keep them off the ground (I just repurposed mine from a cheap greenhouse). That will keep your roots from being too cool. The light will cover your heating needs!!! 16 hours/18 hours of light will bring the heat up enough for it to stay warm while the light is off). I found my plants are fairly good at keeping their humidity and temperature pretty consistent in my basement. I have the same size grow tent. Something to consider is the Mylar, being so highly reflective, helping with efficiency, but also as an insulator. I’d be more worried about circulating air AROUND your grow tent. Do some small oscillating fans, a normal, cheap intake fan, and spend your money on the carbon air filter/scrubber and exhaust fan setup.
Heat and humidity are inversely proportional. When heat is high, humidity is often low and raising humidity will lower temperatures. (The leaves expel water to cool themselves). A super cheap way to raise humidity in your grow tent is literally just a glass bowl of water in the bottom. It won’t solve major humidity issues, but it will help some.
I’m a first time grower and
avid researcher and this is just what I’ve gathered that’s helped me the most.
don’t spend money that you don’t have to!