So I'm working on leveling a Shaman who is currently level 18 - and I am putting my points into the Elemental tree. I've healed a couple of randoms already without any issue. (I have both a Resto Druid and Holy Priest at lvl 85 so healing is nothing new to me) I got into one last night and right as we got to the first boss, one of the Slimes spawned and aggro'd onto me. The tank ended up dying because I was trying to run closer to him and my heal just didn't go off in time.
As we ran back, the tank pointed out that I was healing as Ele and that I really should be Resto. She is geared in full heirlooms (save for the helm) and every time my heal lands on the tank, it brings him back to full health and a large portion of it is over healing. (I currently have only Healing Wave as my only means to heal with).
Anyways, my question ultimately is this - should I be spec'd resto to heal at these low levels and why? And if not, around what level should I start healing Randoms as a Resto Shaman? My thoughts were probably somewhere around level 30 when I can pick up Dual Spec.