Tarantulas can't regulae their own bogy temperature because they are not warm blooded. This is why temperature is so important for them. For most tarantulas the temperature should be about 70-75 degrees. Don't worry if your temperatures drop a little or goes up a little because in the south west desert of the US were some spiders live the temperature can go below 0 degrees! Another thing About heat is that some tarantulas keepers shorten and lengthen the time they turn off and on their T.'s lights seasonally. This is probably very affective, especially for breeding, but not needed.
Also remember to mist your T. to create more humidity. All species vary on how many times they need to be misted a week.
Space Heating is were your house temperature is fit to suit the needs of your and your tarantula's needs. But if you put your house temperature to low it could kill your T. You can also space heat a room, but if you have two or more tarantulas from different parts of the world they would need to have different temperatures. All and all, though space heating can save you money, I wouldn't recommend it.
Electric hot rocks are OK, but I'm not to sure about them. This is because I now that when it gets to cold some lizards would sit so long on there hot rocks that there bellies would burn and scare. I'm not so sure about this with tarantulas, but I wouldn't take any chances myself.
Good, old fashion light bulbs. This is what a lot of keepers, including me use. You can use a light on the out side, top of your tank for about 12 hours on and 12 hours off. You can use a timer if you have the money. A good idea is to heat half of the tank so it can bask or cool down. You can use a black light or a red like if you wish, but I don't.
Heat Pads under the substrate is good for airiel tarantulas. If you put it under the tank for burrowing species they will get cooked! Because they are trying to get away from the heat when they burrow and when it gets hotter they will dig down lower, but it will just get hotter until they fry. For these species put the pad on the side of the tank. Also, like lights put the pad on one side of the tank so it can bask or cool down.
Also remember to put in a thermometer. A thermometer will allow you to monitor the temperature of the tank. Put the thermometer down almost touching the substrate. This way you can tell the temperature of the substrate and the air.
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