What size Ultratherm for 10 gallon tank

[Acohen]

I have a 10 gallon tank and two smallish heaters on same side of tank (zoo med) which I bought before I realized they weren’t very good. The temp on my acurite is usually between 77-80. I ordered an Ultratherm and wasn’t sure what size so I emailed bean farm and they suggested an 11x17. I didn’t realize this is the complete length of the tank . I’m afraid to switch it out with the other heaters because I know there’s supposed to be a warm side and cool side of the tank, but this one is so big I’m afraid the tank will be too hot & once I stick it to the glass that’s it. Any suggestions in the correct size Ultratherm for a ten gallon tank, or is this 11x17 ok? Also, I have about 5-6 inches of substrate, so if I stick the Ultratherm to the back of the tank it will cover the complete back and NOT be above the substrate line.
Thanks

[wodesorel]

I have a very cool room - usually between 50 and 65 degrees, especially in winter. I've always used a pad that covered top to bottom. I use Flukers, so it's been an 11x11. Temp in the tank has stayed around 77-82 which is perfect. BUT, I insulate the crap out of my tank! Uninsulated it wouldn't get nearly that high.

Your temp is already kinda perfect, so I'm not sure if you need a new UTH. And if it's staying that high already then the extra wattage may push you too high on a pad that size.

HOWEVER, slapping it on uninsulated will probably work perfectly. If you wanted to try, I'd suggest doing it when no molters are down. I heat my substrate because I like giving them the option of a warmer moulting location, which some do want! They can't move once down though, so heat shouldn't be started while they are stuck in place.

The other option is buying a thermostat with a probe for inside the tank. It will turn the pad on and off at the right temperatures so it never gets too hot or cold.

[Acohen]

Thanks for responding! I will probably wait because I have 2 that are down at the moment, or I’ll just leave it as is. I thought 77 might be too low, but my humidity is great so I really don’t want to start messing with everything.