Quote Originally Posted by dkatz4 View Post
I'm gonna sort of piggy back on KMG's comments. First of all, i dont want to knock your DIY spirit, but i think the problem is that even thought RHP's and CHE's both use IR to heat the cage, they work in different ways (wow, that was a lot of acronyms!) Full disclosure: I do not know how RHP achieve their heating results with such low surface temps, and i surpassed my 5 minute google limit researching (its a forum post, not a term paper, right?) But basically, and i think this is what KMG is getting at, just because a RHP heats effectively with a low surface temp doesn't mean a CHE will also heat effectively with the same low temp.

Or maybe that is not what you are getting at at all.

Again, I'm really not trying to dump on your idea, please tell me if there is something that i am misinterpreting here.

Actually, RHP's and CHE's both heat the same way. Except an RHP spreads the heat over a much larger area, and a CHE concentrates it. Either way, it's a heat coil (essentially a big resistor) that heats up; it's just a question of how much and how spread out it is. If you compare a 100w CHE with a 100w RHP, they both make about the same amount of *total* heat. If you dim the CHE until it is the same temperature on the surface as the RHP, it's only putting out a fraction of the heat because it is so small. Picking numbers for convenience, let's say you had a RHP that was about 10" x 10" (100 square inches) and 100 watts, and a CHE that is also 100w and has a surface area of around 10 square inches. If you run that CHE at 10% power, it would heat up to roughly the same surface temperature (all else being equal) as the RHP. But it's putting out a lot less total heat because it's smaller. If you set ten of them next to each other, all running at 10% power, you'd essentially end up with the same thing as one 100w RHP.
But basically, a 100w CHE running at 10% power is a 10w RHP. If your enclosure requires 100 watts' worth of heat, 10 watts isn't going to do it.

Incidentally, a UTH (or heat tape) is basically exactly the same thing but even more spread out and made to be very thin so it can fit under things. A ~20w UTH has a similar surface (actually smaller probably, but I'm rounding off to easy numbers again) area to a RHP in the ~80 watt range. In other words, power that 80w RHP down to 25% and it's basically an absurdly fat UTH. The reason a UTH does not heat the air well and also has a real possibility of overheating is that in normal usage it is insulated from below by whatever the enclosure is sitting on, and from above by the substrate. Insulation means that heat that's being produced does not escape; so the temperature can climb even with relatively little power input.

What it boils down to is that all of these heating devices basically work by making coils inside them get hot. The difference is just a question of how much surface area the wattage is spread over.