Where is the Wall of Fire steam engine trick from?

[Eaglejarl]

I remember reading a post somewhere on the intertubes where someone calculated the power output of a Wall of Fire. ('power' in the physics sense) The calculation went something like this: "Wall of Fire can melt X inches of ice, which means it outputs this many calories, which means...." I cannot seem to find that again; does anyone remember where it's from?

[Fouredged Sword]

That would be a VERY sketchy calculation. The problem is that a wall of fire turns ALL water in it's square into steam, per RAW. Given a strong enough pressure container (NI due to fantasy materials) and enough decanters of endless water, you could generate near infinite power output.

[gomipile]

The problem is that a wall of fire turns ALL water in it's square into steam, per RAW.

Wall of fire does not have that rules text. Wall of magma does, however. That, and the fact that wall of magma is explicitly anchorable to stone walls, is why wall of magma is used in the steam engine/rocket builds.

[Eaglejarl]

Wall of fire does not have that rules text. Wall of magma does, however. That, and the fact that wall of magma is explicitly anchorable to stone walls, is why wall of magma is used in the steam engine/rocket builds.

The only RAW that I see for this is:

"Casting create water on the surface of a wall of magma creates a cloud of steamy fog that fills a cube with the dimensions of the length of wall affected. The fog dissipates after 10 minutes."

Where do you see that it vaporizes all water in the square?

[Fouredged Sword]

Sorry, I stand corrected. Wall of magma is the spell used due to that text.

[asnys]

I tinkered with various D&D rocket engines for a while, and may eventually finish my article on it and post it. It's tough, because so many spells don't have enough explicit description to figure out the physics of it. I ended up settling on an approach using Decanters of Endless Water, and then using Blast of Flame spell traps to turn the water into "fire", which I modeled as super-heated air.

There's arguably better ways to do it, but it depends on questionable rules interpretations. In particular, many people miss that Conjuration (Creation) spells, according to the explanation of the descriptor, do not actually create matter, only change its form, while I've yet to find an evocation spell that explicitly leaves lingering matter behind. But I don't own many books, so there's probably some spell or magic item that I missed.