Quote Originally Posted by Brixxart View Post

But... my 20g tank doesn't seem to be keeping heat. at all.
The thermal conductivity of glass is a fair bit higher than most commercial plastics (polypropylene, PVC, polyethylene, etc.) which means that it won't hold heat well by comparison. This is one of the reasons people tend to recommend plastic enclosures over aquariums. Also, glass makes a space feel much more open compared to an enclosure which is opaque on 5/6 sides or overall semi-opaque like a tub. In regards to your ambient temps in your house, while not optimal, a ball python is unlikely to suffer any major issues from a 72-75 F ambient as long as you have an 88-93 F hot spot that allows it to raise its body temperature to the required levels for thermoregulation (high 80s) in the short term.

People usually don't recommend heat bulbs for two reasons: (1) they can be bright and without good hiding places, can cause unnecessary stress, and (2) they can substantially reduce humidity. You'll find most people use either (a) UTH heaters such as flexwatt or ultratherm, or (b) radiant heat panels. These heating methods tend to preserve humidity and do not give off unnecessary light. If I were you, I would do the following:

1. As others have noted, get a good thermostat, you will need it for pretty much any heating source you will use.

2. I would move the snake from your 20g to an appropriately sized polypropylene tub. Thicker plastic is better, but you won't have much control over this parameter in a commercially offered tub. Almost any local store (walmart, home depot, lowes, etc.) should have some. Theres several threads that can show you how to set this up.

3. Once you have your tub set up, you have an enclosure that will work for the time being. After you have your snake situated you can decide if you want to stick with tubs or move to a plastic enclosure designed for reptiles. With plastic enclosures (see animal plastics, constrictors NW, boaphile, etc. for examples) or larger tubs you can use radiant heat panels. These operate similar to the suns radiant heat. The heat downward and heat up objects which give off heat to the environment. The effectiveness of these in heating a cage depends on a few variables such as the thickness and insulative properties of the enclosure walls (read: thick plastic is your friend here) and also the thermal mass of objects in the enclosure. Alternatively, you can heat the room via space heater per monks98 suggestion and provide the appropriate hot spot with UTH.