You have to use it for best noise reduction. The temperature drops up to 5C during an exposure. That would make matching darks very difficult causing unnecessary noise in the image. I set it at the nearest temp at least 10C below ambient that I have in my dark library. While you can calibrate to a known temperature using darks and bias frames taken at a different temp I prefer to take all shots at a temperature I have good darks taken at. This removes the need for a bias compensation and to me gives lower over-all noise in the final image. But even matching to a temperature doesn't work unless the image was taken at a stable known temperature. Letting the atmosphere set the temp prevents good noise reduction. Going colder than 10 below ambient has the problem that the front (side toward the objective) of the optical window freezes over, even with the extra heater I got from SBIG. The air on the back side is kept dry as it is a mostly sealed chamber. But in winter the front side can get so cold it drops below the dewpoint and your imaging is cut short. Even at 10C below ambient I've had it frost over on me in a place or two. This leaves a hole in the image. Quite a pain.

Rick