Water heater works great for terrarium

[tropterrarium]

I mused previously whether a water heater could heat a terrarium instead of using some sort of heat mats. I have a 90 gal terrarium (see here for picture) and put three 11x17 Exo-terra rainforst heat mats 25 watts each under the tank. They turned out to be insufficient to keep the tank above 60F at night now as it gets cold in SoCal. I added a 100 W Rena Smart heater to the waterfall, set it to 85F, and the terrarium stayed at 70F throughout the night. Additionally, the warm water also keeps humidity high, as warm water has a higher water vapor pressure.

Comparing prices, the water heater is much more economical at $25 compared to >$100 for the three heat pads.

Can one just do away with heat pads? One thing to consider is providing heat to the root zone of the potted plants. Under side heat is often applied when growing plants from seeds, so I wonder wether rooting is encouraged with bottom heat. Any opinions, observations?