Like mentioned, you need to experiment. I personally only use RHP for my 48x24x14 PVC cage for one of my BCI girls and it heats it fine. And for my other 2 girls, I use just a CHE all set with Herpstats in 40g breeders temporarily and it works fine there. I do keep my house kind of warm though at around 75F. I'm not too sure about BRBs but I know with BCI and BPs, you don't necessarily need a hot spot per say as long as the ambient temp is warm enough. A RHP will raise the ambient temp and can provide a warm spot assuming you have something under it to warm. A UTH will only provide a warm spot, not heat the air. And also it depends on your substrate. I use about 2" deep aspen so a UTH for me would be worthless but the RHP does heat the aspen under it.