grow space temp and flowering

This is my first time growing, and my space is located in my basement which is about 40 degrees. I built a space out of wood and put a space heater in it. My space is about 60-65 degrees with the lights on (HPS). I dont know the temp with the lights off, I dont go into the basement during the dark period. I had no problem with the veg stage at this temp (my plants got about 30 inches tall in about 46 days (about 6 and a 1/2 weeks). I know growth depends on the strain but is this normal growth rate and do you think my space is too cold for maximum flower production? I would just turn the space heater but I fear i may burn the bottom of the plants (I did this to a few when they were younger.)
Any advice would be appreciated.

Your grow room could be a bit warmer but it isnt overly cold and your plant seems to be growing at a normal speed for a novice.
Well Done!!

Thanks,
Growzaa

heat usually isnt the most limiting factor. If you plants are growing good, they should grow almost 2 feet a month. If you are worried about heat, get a thermostat with a max/min setting on it so you know the temp. If they get below 50 degrees you will notice them growing quite a bit slower