The Voron 2.4 350 Carbon Filter That Doubles as a Chamber Heater

Most carbon filters sit inside the chamber, where the heat slowly cooks the activated carbon and shortens its life. This one mounts externally on the rear panel of the Voron 2.4 350mm (LDO kit) — the carbon stays cool, and the filtered air returns into the enclosure through a duct near the deck, or under the heated bed with the optional diffuser.

The result is a filter that doubles as a chamber heater: +6–8°C measured, holding a steady 60°C chamber at just 50% fan speed (ASA at 245/100). No draft on your prints, no warping, no first-layer issues from direct airflow.

And it's not a claim — it's measured. This filter has been validated with a dual VOC sensor setup (details at the bottom) logging real contamination data across months of ASA printing.

Tool-free cartridge: pull it out, refill ~370ml of carbon, slide it back. Ten seconds.

How the airflow works

Air travels in a single closed loop through the filter assembly:

• Hot, VOC-laden air is drawn from the top of the enclosure into the filter body

• The air passes through the activated carbon first — carbon is upstream of the fan, so the fan never handles contaminated air directly

• The blower fan pushes the filtered air down through the external return duct

• The air re-enters the enclosure through the Deck Inlet, near motor B

• From there it either rises directly into the chamber, or passes under the heated bed first if the Under-Bed Diffuser is installed

The chamber heater part — why fan speed matters

Running the fan warms the chamber; stopping it lets the chamber cool. This happens through two different mechanisms depending on your configuration:

Standard configuration (no diffuser): hot air naturally stratifies at the top of a sealed enclosure. The fan pulls this hot air from the ceiling, filters it, and injects it near the base — forcing circulation that breaks stratification. The fan isn't adding heat, it's redistributing heat that would otherwise sit uselessly at the top. The chamber ends up warmer and more uniform.

With the Under-Bed Diffuser: the fan pushes filtered air into the space beneath the heated bed, where it actively absorbs heat from the back of the bed (100–110°C for ASA) before rising into the chamber. This is a true forced heat exchanger. Measured result: +6–8°C chamber temperature at only 50% fan speed (from ~53°C to ~60°C, ASA at 245°C extruder / 100°C bed).

The Deck Inlet and Under-Bed Diffuser are included in the files:

• Deck Inlet — sits on the deck panel and receives air from the external return duct through the rear panel opening

• Under-Bed Diffuser — connects to the Deck Inlet via slip fit and disperses air under the heated bed

• Both are removable without tools — they simply rest on the deck panel, no fastening to the frame

• A minor modification to the Z belt guard is required to clear the diffuser

• Print both in ASA

⚠ Important: because the fan has this dual role (filtration + heating), running it at 100% continuously during long prints can overheat the chamber. Download and read the PDF for the temperature-aware Klipper macro — strongly recommended with the under-bed diffuser configuration to keep the chamber from exceeding 60°C.

Key features

• Tool-free carbon replacement — pull the filter cartridge up and out, refill, reinsert

• Following the same philosophy as the Panel Glide System, both the filter cartridge and the rear panel with return duct can be removed independently without tools, for easy printer maintenance

• Filter slides into a dedicated flange support mounted on the rear panel

• Return air duct routes filtered air back into the enclosure — optional Under-Bed Diffuser included for active heat exchange under the heated bed

• Stainless steel mesh as primary screen — for those without metal mesh, a printed alternative is included (no top/bottom layers, gyroid infill 20%) and can be easily replaced when needed

• Approximately 370ml of activated carbon

Required panel modifications

• Drill a hole pattern in the upper rear panel where the filter draws air

• Cut a rectangular opening in the lower rear panel for the return air duct inlet

• A single full-size reference STL is provided for the rear panel — slice it in your slicer and print only the section(s) you need (the part is too large to print in one piece). A PDF guide with all required cut-outs and hole positions is also included.

Assembly notes

• Cut the stainless steel mesh into a circle using tin snips (sheet metal shears), then secure the retaining ring on top with two drops of CA glue. The same applies to the printed mesh alternative — CA glue or acetone works equally well.

• The two return duct sections (upper and lower) are printed separately — they fit together with a press fit and no glue is required. However, acetone can be used for a permanent bond if preferred.

• Before drilling, verify that the hole positions on the printed reference section match your assembly. Minor scaling differences may occur depending on your printer calibration.

• For the air intake hole pattern: first drill all holes at 2mm using the printed reference section, then enlarge to 6mm. Drill from the visible (outer) face of the panel, at low-to-medium speed with light pressure. Take it slow — most rear panels (acrylic on LDO kits, or printed ABS/ASA) can chip if you force the drill. Lightly deburr after drilling.

Hardware required

• GDSTIME 120x32mm 24V DC blower fan

• Activated carbon pellets 3-4mm

• Stainless steel woven mesh (optional)

• 3x M4 heat inserts (fan mounting)

• 12x M3 heat inserts (ASA parts)

• M3 and M4 screws

Notes

Return duct dimensions are specific to the 350mm frame. Users with different frame sizes will need to adjust duct length.

VOC Monitoring — the proof (Optional Add-On)

I've added real-time VOC monitoring to track filter performance during ASA prints. This is a separate electronics project that works alongside the carbon filter:

Sensors:

• 2× BME280 (temperature + humidity — one inside enclosure, one in room)

• 2× SGP41 (VOC detection — enclosure intake and room ambient)

Architecture:

• Pico W2 running MicroPython reads all 4 sensors

• Data sent via USB serial to a Python service on the Voron RPi

• Published to local Mosquitto MQTT → Moonraker sensor integration

• Custom web dashboard (matplotlib) on port 8080

What it shows:

• Real-time VOC levels (Sensirion Gas Index Algorithm)

• Temperature and humidity (enclosure vs room)

• Filter efficiency percentage (are VOCs being captured?)

• Long-term trend with 24h moving average (is the carbon degrading?)

Key finding: Fan speed matters more than carbon freshness. At 30% fan speed, the filter couldn't keep up with ASA emissions. At 100%, filter delta went from consistently negative to +60-100% positive. The carbon wasn't saturated — it just wasn't getting enough airflow.

Software developed with Claude (Anthropic) — dashboard code, Klipper macro for proportional fan speed control, and data pipeline architecture. All hardware design and assembly is my own work.

The monitoring system is a custom electronics project (Pico 2W + dual BME280/SGP41 pairs) built to validate this filter with real data. I currently have no plans to publish it as a standalone model, but if you're building something similar, drop a comment — happy to share details.