You need the vent holes Ideally the ambient air temps should be around the 78-85 range and cool surface in the 80 ish range. You need to build a gradient, 1/2 the floor covered will not alter the ambient temps just make the gradient that much harder to manage. It goes against most of the commonly accepted knowledge. UTH drop off quickly there usually is no gradient at all so your hot spot is simply too large and the temp usually drops off sharply outside the area it is. UTH do not alter air temps in any substantial way so closing off ventilation is begging for health issues and increases the potential for RI.

http://ball-pythons.net/forums/showt...ons-The-Basics

I live in Nova Scotia so I get cold. Sadly tubs do not hold heat well at all. The solution most use is to heat the room to 80º the correct ambient temp. that is over kill for a single snake and tub. I don't usually suggest tubs in single set ups due to the very limited heating options. The only real choices are uth and they simply do not touch air temps at all. One method some have used is to place the tub in a open fronted box and have secondary heating in the box (regulated bulb) to keep the cool end and air temps correct with out resorting to heating a huge space. Many suggest solutions with out discussing the downsides. Tanks are have many more heating options and humidity is simply not that critical, heat is.

alternative set up for aquariums...
http://ball-pythons.net/forums/showt...arium-Solution