My grow tent is sitting in my basement, which norm...

yes im using led lamp like heat source too. Normal temperature in tent was around 25°C. Then i bought,, Orca Grow Film and temperature increase to 30°C

Cheap ceramic heaters, low draw (170-250Watt) will give you what you need and don't draw enough to trip a breaker. Everything in your tent is isolated. That little heater will probably give you an additional 4-6 degrees in the tent space. 18/20.4 degrees at this stage of growth is very, very low and I would recommend upping that number (if you're able too) to 25 degrees-ish. During Veg and in the day cycle of flower, I do depend on my LED's to provide the extra heat I need. But in night cycles, I have 2 ceramic heaters hooked up to a Titan Digital timer to trigger 5 minutes after lights out and will end their cycle 5 minutes before lights on. They're never on at the same time just to make sure I'm not overloading a circuit (I live in an older house. If you do too, circuits are usually loaded right up compared to newer homes). I also grow in a basement sub-level and share two outside walls with the tent, so I hear you on the temperature fluctuations/issues. Those little ceramic heaters are about 20 bucks each and the Titan Digital is also about 20 bucks. If it's in the finances I highly recommend picking up this second timer and another heater. I use Honeywell's Heat-Bud unit because it has great safety features and isn't a fire hazard like others I've tried (and then brought back) and only draw 170-220 Watts (low-high functions). No matter what course of action you go for; Ceramic, oil, IR, doesn't matter, just as long as those temps get raised a tad. At these temps they will grow but slower then normal. Optimization is key👌. Good luck my friend. You're good!👍

I'm currently using my vivosun 300w to heat my tent since it sits by the window and it's running around 77 - 81°F so it's possible.

I had that same problem, I couldn't get my plants to take off during winter. I bought a used pet heating pad on ebay that doesn't turn off, or get real hot. I run it when lights are off and the first 2 hours of light on. So in my 18/6 its on 8 hours with a timer. I noticed a change right off, my plants love it, especially when young, clones and in veg. Not saying that is the answer for you, but think outside the box, you will solve it Peace✌️

I have a very similar situation as you. I have an unfinished, poorly insulated basement. My temps are roughly 14 C lights off (no additional heat) and 21 C with my 4 LEDs running. Lights on there is no issue but lights off is a tad too cold. I've bit the bullet and invested in a small electric oscillating heater from Home Depot for 40$. It brings up my night temps to 20 C, however 1 month's use cost an additional 80$ in Hydro Bills. I'm a newer grower and never used MH, HID or HPS but I'm assuming if you switch you won't fix you're heat loss issue because during your dark period you're temps will still be too low as tents lose heat fast. I think your best bet is a heater, my two cents, anyway good luck with the rest of your grow!!!

You could try insulating your basement area or covering the tent in some thick material perhaps? Or putting a very small heater in the tent but don't have it on all the time! And keep a good eye on it. 🌱👍

Use an oil radiator for warmth when your lights are off, on the opposite timing of your lights

yes they keep my room warm and have lights on at night when its coldest

Adding to my above questions, basically I'm wondering if I swap my LED for HID or something that puts out heat decently, if it will warm my tent enough to keep outside the tent at 10 degrees. If anyone has any experience with this or can give me some temps for their outside tent temp vs inside tent temp with whatever lighting you have (not LED)