I wish I could find my instruction sheet for my JohnsonC...then I could be of more help. I don't remember what "sp" is...but "dif" simply means how many degrees do you want to fluctuate before the t-stat kicks in. For our use, that is best set to "1". Then, the t-stat cuts on or off when the temperature gets 1 degree off of the setting you've given it. This means more "clicking"....but keeps the temps more stable over the long haul.


As for the temp differences you're reading....a number of things could be causing that. First thing to consider is the t-stat probe placement. If it's tucked between the flexwatt and the tub underneath, then it will be measuring the hottest point of the flexwatt.

If you have your thermometer probe placed on top of the substrate inside the tub, then it is measuring something entirely different.

The heat the flexwatt gives off is partly lost to the air beneath it and if you have too much of a gap beneath it, you could be losing a lot of heat there. A layer of "Reflectix" over the bottom of the tub can help fix that. (A sort of aluminum-covered bubblewrap found at any hardware store...easily cut and taped into place)

Also, if you have a thick layer of substrate, that will be absorbing much of the heat the flexwatt is giving off, so it must be set at a high temp in order to heat the top layer of substrate to proper temps. This is not ideal because there's always a chance of the snake snuggling down to the bare bottom of the tub and getting burned. This is best fixed by having a minimal layer of substrate...whether paper or aspen or bark....just enough to cover the surface of the floor to absorb waste is all you need. They don't need a "cushion" of aspen or anything.

I use two sheets of newsprint...my JohnsonC is set to 94 and the temps on top of the paper over the warm flexwatt stays at 91 inside the hide.

ALSO....I had trouble keeping the "cool" side of the tub warm enough with just one 12x11 piece of flexwatt. We just keep the house cool. You can try insulating with a blanket over the cool side, but that also holds in excess humidity. (My personal experience.) I used a small space heater to warm the area around the tub so the ambient temps there would stay around 80-82....until I was able to get a second t-stat and a second bit of flexwatt to set up two separate warming zones for the whole tub.

Hope all that rambling makes some sense!