40 gallon tank heating question

[CalamityJane]

Hi! I am new here and SO happy to find a place to get answers. Thank you in advance.
I am moving my growing crabs to a 40 gallon front opening tank. ** They are not in the new 40g tank yet - I'm just preparing it & having heat issues.
I had a piece of plexiglass cut to snap into the top and any minor "cracks" are taped over with my sons black soccer shoe tape (which is WONDERFUL for this application as it is a fabric & sticky enough but not tacky and easy to take on and off repeatedly)

The substrate is a mix of Eco Earth & play sand. and is 6 - 9 inches deep.
I have 2 UTH pads covering the entire back of the tank above the substrate. (one is a 50/60g UTH and the other is 40/50g)

PROBLEM: I didn't realize how wet the play sand was as I mixed the 2 substrates together - so I'm using a room heater to warm & dry it.

QUESTIONS: In your experience (in a normal 68 degree room) how many UTH pads are needed for a 40g tank to remain between 75 & 84 degrees?
Do I buy more UTH
Do I use insulation or both.
Do I need to use UTH on the sides of the tank too?

[wodesorel]

One 35x11 Ultratherm UTH, insulated to reflect heat back into the tank as it's double sided, is usually enough for a 40 gallon. Insulating the top will also help retain heat, as heat rises. Not all brands of UTH create heat equally, nor can all of them be safely Insulated! Ultratherm and Flukers can be, but only Ultratherms are made large enough to get away with using a single pad on bigger tanks.

[CalamityJane]

Ok thank you.
So I just ordered the Ultratherm UTH in 11x35 -
currently I have on it 2 of the "sticky type" UTH - It does fill nearly the entire back wall. But the glass is HOT! How hot is too hot. I can put my hand on it - but it becomes painful after 3 sec. It's hot. When I had those UTH's insulated with foam it was even hotter.
Do the crabs just stay away?
THanks.
Amy.

[curlysister]

If you have no crabs in there, and the sub is too wet, just open the lid and put a fan on it! It will dry out pretty quickly.
A note about the 'sticky' type of UTH - do not insulate over top of them, as it is a fire hazard.
By having the heat source on one (or more) sides of the tank, there will be a natural gradient of heat - it will be hottest closest to the heat source and coolest farthest away from it. I have measured the temp in both places, and in the center (and I leave my thermometer in the center). The crabs will move away if it is too hot, and seek out a cooler part of the tank.