Can you warm yourself up with Fire Bolt?

Question

During my last encounter my 3lvl wizard fell into a trap with freezing water below. He managed to save himself using Levitate, but during my party's post-game discussion there was a question of getting out of freezing water into an even more freezing air (now wet through) and how it should impact a PC.

A spellcaster using a Ready action can keep any spell with a casting time of 1 action on concentration until start of his next turn.

When you ready a spell, you cast it as normal but hold its energy, which you release with your reaction when the trigger occurs.

If it's a fire spell and you hold its energy, then it seems reasonable it would release some heat, doesn't it?

Also, even though you can keep cast and readied spell only until start of your next turn, Fire Bolt is a cantrip so you could just repeat the whole process as long as needed to get oneself sufficiently warmed.

And no, my wizard sadly doesn't know Prestidigitation.

Answer 1

It's up to the DM.

In general, spells only do what they say they do. In the introduction to the section "Casting a Spell", the Player's Handbook states:

Each spell description in Chapter 11 begins with a block of information, including the spell's name, level, school of magic, casting time, range, components, and duration. The rest of a spell entry describes the spell's effect.

The description of firebolt (which is its effect) mentions nothing about the mote itself being a reliable source of warmth, and the rules are pretty unclear about what exactly it means to "hold its energy".

In the absence of clear guidance from the rules, this is a DM judgment call.

This Q&A has some helpful guidance for creative uses for spells: Is there a rule for how to handle creative use of spells?. NautArch writes:

Generally, The Rule of Cool* should encourage creative solutions, as long as they fall within agreement of the rules. Ultimately, there is no real guidance as to how to handle this as DM other than 5e giving the DM ability to adjudicate decisions. You've got the freedom, you've got the power, just come up with something reasonable that is fun for everyone.

Fire bolt may still be able to save you here.

There's an important phrase in the description of fire bolt that may give you a strictly rules as written solution:

A flammable object hit by this spell ignites if it isn't being worn or carried.

While holding the spell for warmth is up to the DM's call, the rules are very explicit that a fire bolt can ignite objects, thus providing you with a fire for warmth.