Wort Chilling

I've just invested in a small coil wort chiller. After getting it out of the box I realized something. I'm only boiling 2 or 3 gallons at a time. Why can't I add the other 2 or 3 gallons of water to bring the wort temp. down? Have I been doing it wrong all this time?

As long as your adding good water, go for it. Be careful adding tap water as it will have chlorine/chloramine. Before I invested in an IC that's what I would do. Throw a couple gallons in the fridge and you can drop the temp of your wort pretty quick.

The wort chiller is great if you have a full boil going. If you are only doing a few gallons and topping off with water, you could boil that additional water ahead of time and refrigerate before you brew. Then add your sanitized water to the boiled wort to cool it (but not in a glass carboy!!)

If you are boiling the whole 5 gallons, then the chiller is highly recommended. And if you aren't boiling the full amount yet, then I suggest looking to do that soon. It will likely improve the beer.