Temp Concerns W/400w HPS

Ok, I'm currently vegging with a 4 bulb HO T5 fixture. Everything is going great, had a little problem with some nute burning last week, but a good flushing seems to have took care of the problem. I will be using a 400w HPS fixture when I start flowering. My grow room is 6' X 4' with an 8' ceiling. Obviously I have not had any heat issues with the T5's, but I'm wondering what to expect when I switch to the HPS. I have one fan circulating air in the room and another blowing fresh air into the room. I would rather not hook up a fan to the HPS fixture. Does the 400w HPS put off THAT much heat for a room the size of mine? And if I do need a fan on the HPS fixture, can a small computer fan be rigged up to it and produce enough air to keep cool? Any thought or ideas from the pros?

i have a 400 and 250 in a 4x3x4 with a low power 5 inch and hi power 4 inch inline but did only have the 4 inch inline, vented into room with window open a little, always use a small fan blowing across top of plants towards outlet

I have the fan blowing across the plants. Should that be enough to contol the heat in a room the size of mine?

could still do with an inline fan to extract hot air and to help plants stay healthy, a good air flow is important.