Chapter 2: Exhausts, Heat Haze & VFX Hooks

Created by Sarah Choi (prompt writer using ChatGPT)

Exhausts, Heat Haze & VFX Hooks — Depicting Thermal Output in Mecha Design

A mecha that feels powerful usually feels hot. Exhausts, heat haze, and VFX hooks are the visible evidence of energy conversion: fuel to thrust, electricity to torque, pressure to motion, and friction to heat. Even in worlds with “clean” sci‑fi power sources, there are still thermal consequences—waste heat has to go somewhere. Thermal VFX is how you show that consequence in a way players can read at speed.

This article is a depiction guide for mecha concept artists on both the concepting side and the production side. For concepting, the goal is to design exhaust language that supports silhouette, faction identity, and gameplay readability without turning the mech into a chimney. For production, the goal is to create clear VFX hook points: where particles spawn, where heat shimmer lives, where emissive lives, what surfaces stain, and how effects scale across LOD, performance budgets, and damage states.

Thermal language here is anchored in three ideas: heat generation, airflow, and heat rejection. Exhausts are heat rejection with attitude. Heat haze is heat rejection in atmosphere. VFX hooks are the contract between concept art and the real-time engine.

Why exhaust language belongs in thermal design

Cooling features like radiators and fins show passive or managed heat. Exhausts show active output—moments when the machine throws energy outward. That makes exhausts one of the strongest “power tells” you can design.

Exhausts also communicate operational mode. Idle vents might breathe softly. Combat vents might flare. Sprint vents might pulse. A mech with variable output feels alive because its thermal behavior changes.

In gameplay, exhaust and heat VFX can be used as readability tools. They can indicate “boost active,” “weapon overheated,” “damage state critical,” or “stealth compromised.” Even if the game does not simulate heat, the visual language can still reinforce these beats.

First: decide what kind of exhaust you mean

Not all exhaust is rocket thrust. In mecha, “exhaust” can mean many thermal outputs: engine/turbine exhaust, thruster plume, hot air venting from cooling ducts, steam-like venting from pressure relief, purge jets, or even radiative glow from heat sinks.

Before you draw shapes, decide what the exhaust represents in your world. Is it propulsion? Is it cooling airflow? Is it pressure relief? Is it a weapon vent? Each category has a different visual expectation and a different set of believable hook points.

For concepting-side artists, this prevents random “cool vents” that contradict the unit’s role. For production-side artists, this determines which VFX systems are needed: particles, distortion, emissive, lighting, decals, audio cues.

Exhaust shapes: the silhouette of direction and intent

Exhaust shape is a directional promise. A circular nozzle suggests focused thrust. A slit vent suggests sheet-like flow. A cluster of small ports suggests modular control or distributed cooling. A large rectangular outlet suggests industrial ducting.

A helpful depiction principle is that exhausts should look like they belong to a duct volume. If the outlet is large, the body behind it should reserve space. If you want compact outlets, cluster them and imply internal manifolding.

Exhausts also benefit from secondary shapes that communicate protection: shrouds, heat shields, louvers, and grille lips. These tell the viewer the exhaust is hot and dangerous and that the designers took steps to manage it.

Airflow logic: intake and exhaust relationships

Thermal design feels believable when air has a story: it comes in somewhere, gets heated, and leaves somewhere else.

Exhaust outlets should generally not fight the mech’s own movement. Rear-facing exhausts make sense for propulsion. Side or upward exhausts can make sense for cooling. Downward exhausts can be used for ground effects, braking jets, or debris clearing.

In concepting, you can imply this logic with a few strategic pairs: an intake cluster on cooler surfaces and an exhaust cluster on hotter surfaces. In production, this pairing helps VFX teams place heat shimmer and particles in a way that matches the story.

Heat haze: distortion as “invisible VFX”

Heat haze (distortion) is one of the most powerful thermal cues because it reads as physics rather than “effect.” It suggests heat without requiring smoke.

Heat haze works best in controlled zones: near exhaust outlets, above hot housings, or along heat sink edges. It should not cover the whole mech or it becomes noise.

In depiction, you can communicate heat haze by designing shapes that frame it: a nozzle rim, a duct lip, a recessed vent cavity, or a heat shield that creates a “window” where distortion would be seen.

For production, heat haze is expensive if overused. The concept artist can help by specifying where it is essential (primary exhausts, extreme overheat states) and where it should be subtle or absent.

Radiation and emissive: when heat becomes light

Radiation is heat leaving as energy, and in art it often becomes emissive glow. Emissive is tempting, but it needs discipline.

If every vent glows, the mech reads like a toy. If one or two high-output seams glow—reactor collars, overheat vents, weapon cooling fins—it reads like controlled power.

A strong emissive strategy is to tie glow to states: minimal at idle, brighter at high load, and chaotic or flickering in damage. This lets the same geometry support multiple gameplay beats.

In production, emissive is also a performance and readability decision. A few coherent emissive zones are easier to author and easier to recognize than many scattered lights.

Exhaust as a worldbuilding dialect

Different factions exhaust differently.

A rugged industrial faction might have big duct outlets, soot staining, and thick heat shields. A high-tech faction might have compact slots, clean edges, and barely visible haze. A militarized faction might route exhaust upward or rearward with heavy guards to protect crew and equipment. A stealth faction might baffle exhaust and spread heat across radiators, minimizing visible plumes.

Your exhaust language can also communicate maintenance culture. Units with removable heat shields, standardized nozzle modules, and clear access panels feel serviceable. Units with welded, scorched housings feel like they are pushed hard and repaired under pressure.

Designing VFX hooks: geometry that invites effects

A VFX hook is a piece of design that gives VFX artists a clear place to spawn an effect. Hooks can be obvious (nozzle openings) or subtle (small purge ports, seam vents, relief valves).

The most reliable hooks have these traits: a recessed cavity, a clear direction, a rim or lip that catches light, and surrounding surfaces that can plausibly show staining or heat wear.

Think of hooks as “stages.” A nozzle is a stage for plume. A vent grille is a stage for hot air shimmer and dust flutter. A relief port is a stage for short bursts of steam-like venting. A heat sink edge is a stage for emissive and subtle haze.

If you provide a few strong stages, the VFX team can make the mech feel alive without inventing new geometry.

Hook types you can include on almost any mecha

There are several hook types that are easy to integrate and useful across roles.

A primary exhaust is the main thermal outlet. It should be large enough to read and placed where direction makes sense.

A secondary vent is a smaller outlet used for breathing, idle heat, or subsystem cooling. These can be distributed and quieter.

A purge/relief port is a small, directional port that vents occasionally. These are perfect for expressive bursts during movement transitions.

A overheat vent seam is a panel line or louver cluster that can open or glow in high-load states.

A damage vent is a broken panel edge or ruptured duct that becomes an emergency exhaust in damaged states.

Concepting-side artists can place these as motifs. Production-side artists can use them as consistent attachment points for effects across a unit set.

Surface consequences: soot, staining, and heat discoloration

Exhausts leave marks. Even in clean sci‑fi, heat changes materials.

Soot patterns usually trail in the direction of flow. Heat discoloration often blooms around hot edges. Dust accumulation can occur at intakes and around louver lips.

In concepting, you can suggest these patterns lightly to sell realism. In production, these become material masks and decals that can be tuned per environment.

A helpful depiction trick is to show “clean mechanical truth” in one view and “operational wear” in another. This tells the team what is geometry and what is surface storytelling.

Gameplay readability: exhaust as state communication

Exhaust and heat VFX can be designed as readable signals.

A boost state can be communicated by a plume that lengthens and brightens. An overheat state can be communicated by vents opening, glow increasing, and heat haze intensifying. A stealth compromise can be communicated by visible haze or plume that should not be present.

If you include these states in your concept package—even as small callouts—you help the team align effects with gameplay.

For production, this is also a budget tool: you can define a “baseline idle” effect set, an “active movement” set, and a “critical” set, instead of every effect being always-on.

Concepting-side workflow: design the thermal performance beats

In early ideation, define the mech’s thermal personality. Does it run hot and dramatic? Or cool and controlled?

Then design a small number of primary exhaust shapes and repeat them consistently. Place them where they support silhouette and avoid clutter.

A high-value sheet addition is a “thermal beat strip”: three tiny thumbnails showing idle, active, and overheat. You don’t need to paint full VFX. Just indicate where haze lives, where glow increases, and where vents open.

This approach helps you stay disciplined and gives production clear intent.

Production-side workflow: spec hook placement and constraints

For production, specify hook points in a way that is actionable. Indicate the outlet direction. Indicate whether a hook is always-on or state-based. Indicate any “no effect” rules—like “no smoke in clean faction” or “no glow except overheat.”

Also think about performance. Heat haze and particles are expensive. A few strong, controlled hooks outperform many small ones.

If the mech has LODs, ensure the primary hooks still exist at distance. If fine vent detail disappears, the hook should still read through a larger outlet shape or emissive mask.

Finally, coordinate with rigging and animation logic. Hooks on moving parts need stable attachment and may need to avoid intersecting geometry during motion.

Common depiction mistakes and how to fix them

A common mistake is exhaust outlets with no plausible duct volume. Fix it by recessing the outlet or enlarging the supporting body volume.

Another mistake is exhaust everywhere. Fix it by defining one primary exhaust system and keeping other vents secondary.

Another mistake is glow spam. Fix it by tying emissive to specific states and limiting the number of glow zones.

Another mistake is heat haze used like fog. Fix it by confining distortion to tight zones near hot outputs and framing it with geometry.

Another mistake is forgetting surface consequences. Fix it by adding subtle staining directionality and heat discoloration near outlets.

A paragraph-form thermal VFX pass before you finalize

Before you finalize exhaust and VFX language, ask: have you identified what kind of exhaust each outlet represents (propulsion, cooling, relief, weapon vent)? Do your outlets have clear direction and plausible duct volume? Is there an airflow story with intake/exhaust relationships? Have you provided a few strong VFX hooks with rims, cavities, and surfaces that can stain? Are glow and heat haze disciplined and state-based rather than always-on? And will these cues survive production realities like LOD, performance budgets, and animation clearance?

If the answer is yes, your thermal VFX language will feel believable, readable, and implementable.

Closing: thermal output is the mech’s heartbeat

Exhausts, heat haze, and VFX hooks are how a mech shows its internal effort. They turn static design into something that feels alive and costly to operate. For concepting-side artists, thermal output language strengthens silhouette, supports worldbuilding, and creates compelling “performance beats.” For production-side artists, clear hooks reduce guesswork and give VFX, materials, and animation teams a clean contract to implement.

When your mech breathes heat in a controlled, intentional way, it stops feeling like a drawing of a machine—and starts feeling like a machine with a heartbeat.