Voron bed size and power requirements: planning the heater and supply

Plan a Voron bed by its size: Voron’s sourcing guide pairs a 200 mm heater with the 250 mm bed, 250 mm with the 300 mm bed and 300 mm with the 350 mm bed. Wattage sets how fast it heats, and current sets what your mains and relay must carry. At the same wattage, a 240 V heater draws half the current of a 120 V one. Voron says not to run the bed above 110 °C.

Voron bed heater size by bed size

The heater pad is smaller than the bed plate, so there is room for mounting hardware and a thermal fuse. Voron’s sourcing guide lists one heater size per bed, and its BOM configurator suggests a wattage. The heaters the guide links to come in higher wattages.

Bed (build size)	Heater size (sourcing guide)	Wattage from Voron’s BOM configurator	Linked heater wattage
Voron 2.4, 250 mm	200 x 200 mm	300 W	500 W
Voron 2.4, 300 mm	250 x 250 mm	450 W	Not listed at this size
Trident, 300 mm	240 x 240 mm	450 W	600 W
Voron 2.4 and Trident, 350 mm	300 x 300 mm	650 W	750 W
Voron 0.2, 120 mm	100 x 100 mm, 24 V DC	60 W (sourcing guide)	Not applicable

Voron’s configurator calculates wattage as 0.0055 W per square millimeter of build area, rounded to a standard heater size. The linked heaters are Keenovo pads in 110/120 V and 220/240 V versions. Voron’s sourcing guide says exact wattage is “not critical”, and explains the trade-off below.

How much bed power does a Voron need?

Enough to reach your bed temperature in a reasonable time, without overloading the relay or circuit. Voron puts it this way: “If the mat is underpowered, it will take longer to heat your bed. If it is overpowered, you can use firmware control to have it use less power.” It adds that an overpowered heater at full power “will heat your bed faster but make it more prone to warping.”

Two outside rules of thumb help check a choice. Duet3D, which makes printer controllers, suggests “0.4W per square cm of bed area” for “reasonably fast heating to around 100C”. Tempco, a heater maker, gives 2.5 W per square inch for low heat-up, 5 for average and 7.5 or more for high.

Bed plate	Area	Duet3D’s 0.4 W/cm²	Voron configurator
250 x 250 mm	625 cm²	250 W	300 W
300 x 300 mm	900 cm²	360 W	450 W
350 x 350 mm	1,225 cm²	490 W	650 W

The Duet3D column is our arithmetic from its stated rule. Both methods land in the same range.

120 V vs 240 V: current draw and circuits

Current is power divided by voltage, so the same heater draws half as much at 240 V. A 750 W heater draws about 6.3 A at 120 V and about 3.1 A at 240 V. A 650 W heater draws about 5.4 A at 120 V and 2.7 A at 240 V. Voron’s sourcing guide says to “choose an AC voltage suitable for your region.”

The printer is not the only load on the circuit. A bed heater runs for hours, which makes it a continuous load under the US National Electrical Code, defined as one lasting “three hours or more”. The code sizes the circuit’s breaker at 125% of continuous load, which IAEI Magazine describes as “an overcurrent device being applied at 80% of its nameplate rating.” Add up everything on the circuit before choosing a high-wattage heater.

Best bed heater for a Voron 350 on 240 V

On 240 V, the linked 300 x 300 mm heater at 750 W draws about 3.1 A, under the 4 A that Voron gives for its specified relay without a heatsink. Choose the wattage by how fast you want the bed to heat, within your relay’s limit. The table lists the Keenovo pads Voron’s sourcing guide links to, with their prices on October 1, 2026.

Heater	Size	Wattage	Voltage versions	Price
Keenovo silicone heater	200 x 200 mm	500 W	110/120 V, 220/240 V	$44.39
Keenovo silicone heater	240 x 240 mm	600 W	110/120 V, 220/240 V	$55.49
Keenovo silicone heater	300 x 300 mm	750 W	110/120 V, 220/240 V	$77.69

Solid state relay limits

The relay that switches the heater has its own limit, often lower than its headline rating. Voron’s Klipper configuration notes that “the Omron G3NA-210B-DC5 SSR is rated at 4 amps without a heatsink”, and gives a formula to cap the heater’s power to match: “4 / (Wattage_of_bed_heater / Mains_voltage) = max_power”.

For a 750 W heater at 120 V, that gives 4 / 6.25 = 0.64, so max_power should be at most 0.64. At 240 V the heater draws 3.1 A, under the 4 A limit, so no cap is needed. Duet3D adds that “if your bed heater draws more than about 1/4 of its rated current then the SSR may need a heatsink.”

[heater_bed]
max_power: 0.6     # Voron's default; recalculate for your heater and mains
control: pid

Voron also warns: “Buy a quality SSR (see the official sourcing guide), cheap clones may overheat and fail closed causing a heater thermal runaway.”

Thermal fuse and grounding

Add a thermal fuse in line with the heater, and ground the bed. Voron’s wiring guide says to “add a 115-125°C thermal fuse to your bed heater as an additional safety measure”. Voron’s sources disagree on the rating: its V2.4 sourcing sheet says 130 °C, while the Trident sheet and BOM configurator say 150 °C. Whichever you choose, it must sit above your normal bed temperature and below where the heater fails.

The V2.4 sheet gives the reason for the fuse: “you want the fuse to blow before the heater falls off the bed”. On grounding, Voron is direct: “If using an AC powered bed, be sure to ground the bed regardless of if the assembly manual specifies it or not.” It recommends grounding the frame too, and at least 18 AWG (0.75 mm²) wire for mains, or 16 AWG (1.25 mm²).

How hot can a Voron bed run?

Voron recommends no more than 110 °C. Its wiring guide says: “Don’t run your bed above 110°C, this reduces the lifespan of the adhesive holding it onto the build plate”. A more powerful heater gets the bed to 110 °C faster, but it does not make higher bed temperatures part of the design.

How to compare heated bed options by wattage and flatness

Compare wattage against your bed area and your circuit, and flatness by the plate material. Voron specifies cast aluminum tooling plate for the bed, such as MIC6 or ATP-5, at 8 mm or 5/16 inch. Its FAQ lists rolled alloys such as 6061 and 5052 as unsupported, because they are “not designed to take repeated heating and cooling cycles and will warp quickly”.

Thicker plate is allowed, but Voron notes “your heat up times will greatly increase”. When comparing beds, check three things: the plate alloy and thickness, the heater’s watts per area, and the current it draws on your mains.

PID or watermark for an AC bed?

Voron’s official Klipper configurations use PID control for the bed, with a solid state relay. Klipper recommends PID for beds that support PWM, but warns PID “may turn on and off ten times a second, which may not be suitable for heaters using a mechanical switch”. A solid state relay handles that switching. A mechanical relay does not, so use watermark control with one.

After fitting the heater, tune it. Voron’s startup guide gives PID_CALIBRATE HEATER=heater_bed TARGET=100, a routine it says “will last about 10 minutes”, followed by SAVE_CONFIG.