Need feedback on my plan for heating a 72

[Crabby Abby]

I've not set up my 72 bow front yet because after purchasing the tank/stand and a versa-lid I'm presently lacking the funds for the heat. I'm considering one 50-60g sidemounted UTH, one bottom mounted 10-20g (just because it would otherwise go to waste when I toss the 10 my dog smashed), one day glo and one moon glo which I believe add heat as well as lighting. I'm concerned it won't be sufficient to keep the substrate depth I require for 8-Ball warm enough. Anyone know if it would?Thanks!*edited* Might do both side mounts, not real big on bottom mounts due to unexpected power failures.

[JediMasterThrash]

I don't know what it is, but every time I look for past posts (that probably included archivable material), I can't find them anywhere. It's like all the good info posts disappear. Or the past-post lookup doesn't find stuff that got moved to archives.During the day, underground is definitely cooler than the surface, and all animals that bury during the day will cool off from the sun's heat. As an insulator, the ground will maintain its temp better, so at night, this might invert if the air cools off. But even though the ground is now warmer than the air, it's still the same or cooler than it was during the day.So, to mimmic nature, I recommend using overhead incandescent lighting for heat, as this warms the air and surfaces (and evaporates water to increase humidity), and the lower substarte will stay a bit cooler.When crabs go down to molt, they need high relative humidity, and relative humidity increases as temperature decreases, so they'll have higher relative humidity down in the cooler substrate.If there's an UTH, the lower substrate will dry out fast. Usually the substrate around the UTH is always dry, and this is not conducive to crabs molting. They need most of the substrate moist for digging and successful molting.Also, when the sand over an UTH is moist, and then dries out from the heat, it will brick up, forming rock-hard chunks, which crabs will have difficulty digging through. Luckilly this bricking is usually less than a centimeter high though.I can no longer recommend UTHs at all for main tanks. They were originally designed for lizard habitats, which are suppost to have warm surfaces and dry air. When hermit crabs were first introduced as pets 50 years ago, nobody knew what to do with them, so they just categorized them along with reptiles. The "standard" of using UTHs with hermit crabs came from this, and I don't think it's a very good standard.I do have a small UTH on my 10g ISO, because I didn't have a light for it yet. The UTH still does work quite well, and it heats up a good ocuple inches of sand. But the crabs usually stay buried since the air isn't as warm and there's no natural light. And they prefer to bury in the cool side anyway where it can stay moist at all times.Insulating the bottom of the tank to provide some extra protection against a cooler house is a great idea, though I haven't done it myself yet since my tank is heavy. But I've had more than enough successful deep-substrate molts during the winter to know that the cooler lower substrate doesn't seem to adversely affect them. And I know the crabs love coming out to bask in their repti-sun during the dayI should get a meat thermometer and see what the bottom temp actually is.