Hello,
I know of three companies right now who market and/or sell a heat panel. First their are the Helix heat panels made by the same guys that make the fancy proportional thermostats. Secondly there are Pro-Products heat panels - same guys that make Provent-a-Mite. And finally a company called Enerjoy. I think I've seen the Helix radiant panels on Big Apple Herp, while the Pro-Products are available only on their site, and finally Herpsupplies.com carries the Enerjoy heat panels.
They're all basically the same in terms of construction although the cheapest I've seen are the Enerjoy panels from Herpsupplies. As far as sizing goes, that's a tough question. You usually want to mount the panel on the ceiling of the cage and usually, depending on the size of the cage you want to go for something that covers about 1/4 to 1/3 of the ceiling.
With heat panels, the smaller sizes are chiefly lower wattages while the larger sizes are the higher wattages. I wouldn't use any of them without having them run through a thermostat with a remote probe. We use the heat panels in our display cages at the Wildlife Discovery Center and they seem to work pretty well. They do however have a very "drying" effect on the cages which needs to be taken into account. You definetely need to stay on top of your humidity using heat panels and if neccessary consider using some type of automated humidity device (mister, fogger, etc.), in order to keep your humidity values where you need them for your species.
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Matt Campbell
Animal Keeper, Small Mammal/Reptile House
Lincoln Park Zoo Chicago, Illinois
Assistant Curator
Wildlife Discovery Center at Elawa Farm
Lake Forest, Illinois