It can be bad if you don't have a method for controlling the heat. The snake can overheat or get burned easily.

Digital thermometers with probe are fairly easy to get. Just go to Lowes, Home Depot, WalMart or Target and get one of these:


This is one of the best temperature measuring devices out there, short of a temp gun.

As for thermostats, which control the heat output, there are many choices but hardly any can be bought at a pet store. Most are online only.
The low end, for those who can't spare a lot of money at the time, is the ZooMed ReptiTemp 500R, for $25 or so at ReptileSupply.com Many people say this stat is not worth the money, and you do get ones that fail or don't work from time to time, but I have four running right now that work just fine.



Next up would be the lowest 'Good' thermostats: the Johnson and Ranco. These are around $80 and can be found at ReptileBasics.com.


The high end, but best thermostats you can get, are the Herpstat and Helix proportional stats. These can run $100+, and have many types and features that can make snake keeping easier for the keeper. They can be found at varied sites, just search for them on Google to find the best prices.





Hope that helps as far as finding the equipment. You should get a thermometer and thermostat ASAP!