Heating question

Getting a 24x18x18 exo Terra for my corn but don't know what size to get for it just want him happy and healthy thanks in advance for any advise and wisdom

Apparently you posted this twice. So I'll answer it twice, LOL

just get one that is about 1/3 to 1/2 the size of the bottom. So a pad around 10x12 (minimum) to 18x12 (maximum) or anything in between would work nicely.

UTH are usually sold by wattage estimates and size. If you purchase one that is too small you have wasted your money. I would buy one with higher wattage and regulate the temp with a good thermostat. Zoo Med sells a 24 watt UTH that's 18x8. They also sell a 10 watt snake strip for those wanting that type of UTH. There are too many variables to give one blanket statement of the best, because such things as depth of substrate may affect the desired hot spot.

while it's true that wattage is usually listed, the newby or novice still has no clue what wattage to purchase. Anyone who takes the time to examine the packages will notice that the lower wattage pads are quite small, and as the pads increase in size, so does their wattage. So it's only natural, that a pad large enough for a 24x18 cage will be both a higher wattage and larger footprint than a pad designed for say a 12x12 cage. Most snake owners using heat pads look for a pad that is 1/3 to 1/2 the size of the bottom of the cage. The wattage really does not come into play as it "Will Be" the correct wattage if the person purchases the correct size pad. I failed to mention above, but will do so now, regardless of the brand or size, a thermostat should be used along with the pad, because unregulated, some of those pads get hot enough to cook snakes.

The thermostat is a must. I purchased the smallest pad I could find and it reached over 100 degrees without a stat. A cooked snake is not a happy one..

When you do get your setup, test it to make sure everything is working as designed.