Widen Spell( Tome and Blood: A Guidebook to Wizards and Sorcerers, p. 42)
You can increase the area of your spells.
You can alter a burst, emanation, or spread spell to increase its area. Spells that do not have an area of one of these three sorts are not affected by this feat. Any numeric measurements of the spell's area increase by one-half. For example, a widened fireball spell (which normally produces a 20-foot-radius spread) now fills a 30-foot-radius spread. A widened spell uses up a spell slot three levels higher than the spell's actual level.