Heating grow tent

Hello everyone, I ran into an issue now that my long term heater has died. I must avoid using a space heater since I don't have any available wall outlets dedicated to it or must stretch an extension cord (huge fire hazard) to be able to heat it from the neighboring room. Since the previous one had stopped functioning, the tent has had a week old seedling enduring lights on temps of 66 degrees Fahrenheit. For now, I have been using a 5 gallon bucket which I fill with scalding hot water to slowly diffuse and raise the temperature of the tent by several degrees. Is this a viable method if I was to get an aquarium heater?

I cannot raise the ambient temperature because the house is very energy inefficient and I am tight on money and space heaters are out for the aforementioned reasons.