In order to (a) stop the flambeau getting their arses kicked and (b) stop some slightly silly examples of really big fires not hurting anybody I am assuming that the damages given for fires are based on the damage caused by a small flame of that intensity. An individual or group sized flame will do +5 damage, a Structure sized flame +10, Boundary sized +15, Sight sized +20. Furthermore note that if you don�t increment your range in a roughly similar way you risk some serious blowback.
Level 15
The Writing on the Wall
R: Reach (Arc) D: Special T: Ind
This spell sends a message to the target by burning it into the nearest suitable (probably wooden) surface. The caster must concentrate for as long as it takes to write the message out (which tends to be about a second per letter, since tracing words in fire is no easy task), the spell lasts just long enough to send one message.
Level 20
Generic Sheet of Flames
R: Far D: Mom T: Group
This oh so simple spell creates a group-sized +10 fire, that is to say one doing +15 damage. The resulting ball of flame is about five paces across, and will cause some pretty damn serious fired damage.
Level 20
Eyes of the Flame
R: Reach (Arc) D: Conc T: Ind
As the 4th ed spell of the same name, with its level reduced for my Arcane Connection modifications. The most commonly used Connection with this spell is another fire lit from the first fire in which the images appear. If this spell is cast with an Imaginem requisite those images will be visible to everybody.
Level 20
Sword of the Heart of Fire
R: Touch D: Sun T: Ind
Requisites: Terram
The caster reaches into the heart of a fire and pulls out a sword the precise nature of which will be determined by the caster�s sigil. This sword has a Damage rating equal to that of the fire it was pulled out of, its other characteristics depend on the style of sword.
Level 20
Winters Touch of Summers Day
R: Reach D: Sun T: Ind
This spell cools a person down to the extent that they feel like they�re outside and underdressed in the dead of winter. Nothing they do will warm them and over the course of they day they will begin suffering the effects of acute hypothermia this could well prove fatal.
Level 25
The Blessing and Curse of Fire�s Disdain
R: Reach D: Sun T: Ind
The target of this spell will find that all fires of intensity +15 or less refuse to come within three paces of him. This makes lighting them a bugger and a half, and keeping warm on cold nights a little problematic.