Can't get uth surface temps up enough - options?

[CaliforniaPlaya]

I've got a 40 gallon tank set up and am using an 11x11 Ultratherm UTH. I'm now realizing that I should have probably gotten the next size up. Substrate is an inch of sand below an inch of large rocks. No geckos in the tank yet. Sand is there for the purpose of protecting the glass and cushioning the rocks. They should not be able to access the sand but will monitor (just wanted to get that out of the way).

Have had the heater on for 10 days. Initially just taped on with foil tape. When that wasn't adding much heat, I added a layer of pipe wrap tape (basically insulated foil tape). That helped to get the surface temps up from mid 70's to low 80's. I then added a sheet of foam insulation. That got the surface temps up to 87, but thats it. I've used a couple of different digital thermometers and they read almost identically. With the probe on the very surface of the rocks, I'm getting about 87, 90 if I bury it under the rocks, and 96 if I dig all they way down to the bottom of the tank below the sand and hit the glass. But thats still not very hot. Indoor temps are in the mid 60's to low 70's. Do I just have too much substrate in there for it to penetrate or is this heater just inadequate?

Thanks!!!

 

[5HiddenLizards]

My heaters are the Zoomed UTH...they are directly on the glass. I have about 4 different temps from them. One gecko has a thin layer of coco fiber, just to cover the glass. His reads at 87 right on the dirt. The other is on papertowel & that heater reads 96. The fat tail's heater is under 1in of coco fiber. It reads 90. And the one for my fire skink, which is under 1/2 inch of dirt hits 94.

Since the temps in the house are low, that could make the heaters cooler. During the summer my hot spots were hitting 105. My lizards are in a room that's between 60-65 right now with the cold weather.

 

[Dog Shrink]

Ultratherm runs at a higher wattage than the T-Rex cobra equivelant so 11x11 on a 40 might be too small. Plus they're designed to run at a consistant constant 100 degree output. I run a 6x11 on a 20 long and make temps no prob running a t-Rex cobara mat at 7 watt output. Also how long has the heater been going? When you have that thick a substrait and yes 2 inches is pretty thick, and when it is natural rock it sometimes can take a couple few days for everything to heat up to temp given the nature of thermodynamics and rock surfaces. Rock tends to spred the heat thru the entire surface so you're actually heating a larger area than you would if you were using a different substrait such as vinul simulated slate tiles. If you just got this uth and you really want to go with taht substrait set up, you might want to consider returning it for the next size up imo. Make sure you feel the area above the mat in your tank and you are placing your heat probe directly over the warmest spot you can feel for the most accurate temperature reading.

Also your uth should cover abut 1/3rd of your tank floor surface. Maybe cut down on the sand layer between your uth and slate tile see if that helps a little bit, after all you only need barely a cushion to protect your glass. I would think a half inch of sand would suffice for this application. After all the leos aren't gonna be doing WWE wrestling in there so I don't think you need to worry too much about the glass getting damaged.

You might want to consider replacing all that stuff you have covering your uth with something a little more breathable like this:

It's plastic styrofoam, you can usually find it in packing high end stereo equipment or even pipe wrap is similar (the black/grey stuff that slips over your pipes) if your uth can't breathe properly you may be tripping some internal sensor and it could be shutting down your heat mat sporatically to prevent it from burning up. The foam insulation, is it like the stuff they wrap houses in before they do vinyl siding? If so maybe you can get away with poking it thru with some holes so it can breathe and just use a couple layers of it perforated like that and remove all the tape and just use the board to hold it up. It might take 3 layers but just make sure you perforate each layer. You might also want to consider insulating the sides and back of the tank just for added mesure to make sure you're not suffering any heat loss thru those areas.

Also there are a lot of threads in my posts that go into a lot of detail about uth and all the stuff you're currently going thru. Esp. with a member handle NCBeast. Maybe if you go thru my past posts you could find some more useful information that applies to your situation.

Hope some of this helped.