Thanks Tinyroots for your answer. I went to the website and it seems like I've done what they said so far.

Only other than the ledge on the heater next to two large windows, I have no where else to put the plant for it to get sufficient light in the apt. It's been there for over a week now and the pot remains cool to the touch while sitting on a humidity tray. I also put an extra plank of wood on top of the ledge under the plant keeping it away from direct heat. I did this before with an orchid and it worked fine, so I don't see why it wouldn't work for a serissa.

However, I think it's still safer to tell others to keep it away from any heaters as a rule of thumb.

(people are welcome to give their input.)