Night time temperatures

Hey guys im new to this site and would really appreciate some good advice. I`ve only just started growing and am currently on my second crop. Right now it`s been starting to get cold and I was wondering if anyone can reccomend a heater for my room when the lights are off. I`m currently using 2 small electric heaters. I heard electric heaters are bad because the plants dont like hot air being blown on them. What i did though was i put the two heaters against my wall about 6 inches above the canopy of my plants. They are just barely doing the job and I need something much better. I would like to use something I can plug in so that I can hook it up to a timer. Any advice would be much appreciated.

I can try to help, but first it would be good to know your daytime temperatures and also the nighttime ones.

well basically my daytime temerature is about 27 degrees celcius or about 80 degrees f. at night my room drops to about 21 c or 70 f. thats with 2 small electric heater on at night. my room is larger than necessary too, about 16 feet long and 9 or 10 feet wide. basically i need a really efficient way to heat my room at night because soon my 2 electric heaters arent going to cut it. I also estimate that my room will drop to about 18 degrees c or 65 f if i weren't using my current heaters.