>>I have heard that helix is a good brand of RHP's (is this true?)... LLL Reptile has some medium sized panels on sale I was looking at... i need 3 more and they're about $40 cheaper EACH than the pro products. It's 110 watts, 11"x30".
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>>Is this overkill for my colubrids? the cage is 2x4x2 (l x w x d)
I used the Helix 11"x16" 65-watt panels in the cages I built. My large cages are 42" wide x 24" deep x 18" high. The smaller cages are ~30" wide x 24" deep x 18" high. Retail price on the Helix RHPs I used is now $69/ea. I think I ended up paying around $50-55 for mine, but that was before prices went up and I was able to get a 10% discount on them through JustHerps.com.
Overall, the Helix panels are pretty nice. They smell for a bit when you first plug them in but it goes away pretty quickly. Running non-stop, the 65-watt panels are able to provide a nice 90-80 degree gradient at the floor of my large cages when my snake room gets cold. The temperature of the panels themselves gets up to around 165 degrees according to my temp gun. The further away your floor is from the panel, the more power you need to raise the temperature. I think that if my enclosures were 24" high that the 65-watt panel might not have been enough power to adequately heat the enclosure. Not a problem if you have animals that will climb to get nearer to the panel, but if the species you keep are strictly ground-dwellers...
Mounting of the panels is...kinda kludgey. The panels come with some nice little clips, but the instructions recommend you don't use them with snakes! They recommend that you put scews/bolts through the four corners of the panel. That's what I did, and it works, but it looks a bit jury-rigged in my opinion.
Also, keep in mind that the panels are a bit bulky. They're probably 3" thick and there's a lip around the edge. My snakes love to climb along this lip, which is probably why they tell you not to use the flimsy mounting clips they provide!
Getting the 110w panels for $65 is certainly a bargain. They may be more panel than you actually need, but as long as you put them on a thermostat I can't see any reason no to buy them! Heck, they're cheaper than the 65w panels!