controlling heat/cooling in our grow room

I am finishing up my 20' x 8' x 8' room and am wondering howto control the heat/cooling in the winter time. I am running a 12" max fan taking in fresh air from the attic space above my garage then venting to the outside.
My thoughts are that if the temps outside are in the 35F to 45F range then the room may get too cold.
I will be running 5 1000watt HPS lamps.
Do I need to worry about the cold temps or will heat be a bigger issue for me?

Well, once you get some kind of temperature controller, the unit can turn your ac/heater/fan or whatever on and off as you need. of course if you have a carbon filter it should be running 24/7 during flowering though, i think, someone correct me if i'm wrong.

But yeah, the temp. sensors will know when it is too cold and too hot, therefore keeping the temp within 2-6 celsius of the proper temp. that is how i would do it, all automated. So if your room does get too cold, the cooling fan will obviously be off.. i doubt it will get too cold with those 5 lights in there though

Thanks for the input. I am thinking that heat is easier to deal with than cold but I may be wrong. I am brand new to indoor and ned all the help I can get at this point.
Where I live it is cold and humid in the winter times.
I will with out a doubt be running a controller.
I am going to build an identical room as soon as this one is done, only difference being the second room will be running CO2 with vented lights.

any pictures you can post up to see more detail

no pictures as of yet...it is just a basic rectangle room. When it is turn key I will run a couple nights without mater's just to see what my numbers will be. The more I think about it I am sure heat will be the issue.

Another question is will the 5 1000w lights also help keep humidity low enough when moving the amount of air that the 12" max fan will move?