Electrical Cabinet Heaters: Wattage Sizing & Selection Guide

Enclosure Heating Guide

Cabinet Heater Sizing & Selection Guide: Electrical Cabinet Heaters

Q: Do these electrical cabinet heaters include a thermostat?

The KH800 panel-mount models (125W–400W) include an adjustable thermostat in Celsius and Fahrenheit plus a pilot light. The KH501 convective and KH503 fan-assisted units use self-regulating PTC elements and should be paired with a separate enclosure thermostat or hygrostat for setpoint control.

Choose the right cabinet heater by matching wattage to your enclosure's heat loss, then picking convective, thermostat-fan, or high-capacity forced-air. This guide covers Seifert's 25W–800W electrical cabinet heaters and a four-question selector to narrow the list.

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Sized by Wattage25W to 800W covering condensation control up to large forced-air cabinets.

Self-Regulating PTCOutput adjusts with surrounding temperature instead of a fixed-resistance element.

DIN or Panel MountClip-on DIN-rail bodies and panel-mount aluminum housings for tight panels.

AC/DC or 115/230VWide-range KH501 units plus voltage-specific 115V and 230V models.

Quick answer

Choose a cabinet heater by wattage from your enclosure heat-loss calculation: 25–150W convective KH501 units (110-240V AC/DC) for condensation control in small panels, 125–800W KH800 thermostat-and-fan units for circulated heat, and 250–750W KH503 forced-air units for high heat loss. Match voltage (110-240V AC/DC, 115V, or 230V) and confirm circuit current before ordering.

Find the Right Product

Answer these four questions and we'll narrow the list to your heater.

1. How much heating output do you need?

2. What supply voltage do you have?

3. Do you need a fan for active circulation?

4. Do you need a built-in adjustable thermostat and pilot light?

All Options

Every Seifert heater below, grouped by wattage and heating method. Filter by voltage, mounting, and whether you need a built-in thermostat and fan.

Seifert 501025 KH501 25W 110-240V Control Cabinet Convective Heater, 4.92" x 1.61" x 1.61"

Product Code: 501025

Best for: Small crowded panels needing minimal condensation heat

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Seifert 501050 KH501 50W 110-240V Control Cabinet Convective Heater, 4.92" x 1.61" x 1.61"

Product Code: 501050

Best for: Modest heat loss where panel width is limited

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Seifert 501075 KH501 75W 110-240V Control Cabinet Convective Heater, 5.51" x 2.76" x 2.48"

Product Code: 501075

Best for: Mid-size cabinets with moderate calculated heat loss

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Seifert 501100 KH501 100W 110-240V Control Cabinet Convective Heater, 5.51" x 2.76" x 2.48"

Product Code: 501100

Best for: Larger convective heat loss, same 5.51" body

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Seifert 501150 KH501 150W 110-240V Control Cabinet Convective Heater, 8.66" x 2.32" x 2.4"

Product Code: 501150

Best for: 150W convective heating on DIN rail, IP20

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Seifert 125W 115V Control Cabinet Heater, 5.39" x 4.09" x 4.61"

Product Code: 801125A33000

Best for: 115V panels wanting thermostat, fan, indicator

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Seifert 125W 230V Control Cabinet Heater, 5.39" x 4.09" x 4.61"

Product Code: 801125A44000

Best for: 230V panels wanting thermostat, fan, indicator

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Seifert 200W 230V Control Cabinet Heater, 5.39" x 4.09" x 4.61"

Product Code: 801200A44000

Best for: 230V cabinets needing 200W circulated heat

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Seifert 503250 KH503 250W 230V Control Cabinet Resistor Heater, 5.3" x 3.2" x 4.4"

Product Code: 503250

Best for: 230V DIN-rail cabinets needing 250W forced air

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Seifert 400W 115V Control Cabinet Heater, 7.48" x 4.09" x 4.61"

Product Code: 801400A33000

Best for: 115V cabinets with high 400W heat loss

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Seifert 503500 KH503 500W 230V Control Cabinet Resistor Heater, 6.5" x 3.2" x 4.4"

Product Code: 503500

Best for: 230V high-capacity forced-air heating, DIN rail

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Seifert 503750 KH503 750W 230V Control Cabinet Resistor Heater, 8.8" x 3.2" x 4.4"

Product Code: 503750

Best for: Large 230V cabinets with the highest heat loss

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Which One Should You Buy?

Find the row that matches your setup:

Your situation	Our pick	Why
Small sealed panel, just fighting condensation, DC control power	Seifert 501025 KH501 25W 110-240V Control Cabinet Convective Heater, 4.92" x 1.61" x 1.61"501025	25W convective, narrow 1.61" body, accepts 110-240V AC/DC in tight panels
Modest heat loss but no room for a wider heater	Seifert 501050 KH501 50W 110-240V Control Cabinet Convective Heater, 4.92" x 1.61" x 1.61"501050	50W in the same narrow KH501 footprint as the 25W
Mid-size cabinet needing more convective output	Seifert 501100 KH501 100W 110-240V Control Cabinet Convective Heater, 5.51" x 2.76" x 2.48"501100	100W PTC convective, 5.51" body, wide AC/DC input
150W convective without a fan on DIN rail	Seifert 501150 KH501 150W 110-240V Control Cabinet Convective Heater, 8.66" x 2.32" x 2.4"501150	150W PTC, IP20, DIN-clip, 110-240V AC/DC
115V panel wanting thermostat, fan, and pilot light	Seifert 125W 115V Control Cabinet Heater, 5.39" x 4.09" x 4.61"801125A33000	125W KH800 with adjustable thermostat and selectable fan on 115V
230V cabinet needing 200W with circulation	Seifert 200W 230V Control Cabinet Heater, 5.39" x 4.09" x 4.61"801200A44000	200W KH800, two fan settings, thermostat, indicator light
230V DIN-rail cabinet needing 250W forced air	Seifert 503250 KH503 250W 230V Control Cabinet Resistor Heater, 5.3" x 3.2" x 4.4"503250	250W KH503, 20 CFM fan, PTC, overheat protection
Large cabinet, high heat loss, 230V DIN rail	Seifert 503750 KH503 750W 230V Control Cabinet Resistor Heater, 8.8" x 3.2" x 4.4"503750	750W KH503 with 26 CFM forced air for big enclosures

How These Options Differ

Start with wattage from your enclosure heat-loss calculation, not cabinet size alone. For pure condensation control in crowded panels, the KH501 convective line runs 25W (501025) and 50W (501050) in the same narrow 1.61" square body, then steps up to 75W (501075) and 100W (501100) in a wider 2.76" body, and 150W (501150) in a taller housing. All KH501 units accept 110-240V AC/DC and rely on natural convection, so they suit smaller, well-sealed enclosures. When you need active circulation and a built-in thermostat, the KH800 panel-mount line adds a fan, pilot light, and adjustable setpoint: 125W in 115V (801125A33000) or 230V (801125A44000), 200W 230V (801200A44000), and 400W 115V (801400A33000). For high heat loss with forced air on DIN rail, the KH503 line delivers 250W (503250), 500W (503500), and 750W (503750) at 230V. Confirm your available voltage and circuit current before ordering.

How an electrical cabinet heater works

An electrical cabinet heater keeps internal enclosure temperature above the dew point so moisture doesn't condense on boards, terminals, and contacts. Two designs appear in this range:

Convective (KH501): a self-regulating PTC element warms an extruded aluminum radiator; natural convection carries heat upward. Quiet, no moving parts, ideal for small sealed panels.
Fan-assisted (KH503, KH800): a fan forces warm air through the cabinet, eliminating cold spots in larger or densely packed enclosures.

The PTC element self-limits: as it heats, resistance rises and output falls, capping surface temperature and reducing power draw when the surrounding air is already warm. That makes PTC heaters safer in confined spaces than fixed-resistance coils. Pair convective PTC units with an enclosure thermostat or hygrostat; the KH800 line has that thermostat built in.

Cabinet heater wattage sizing

Heat loss, not cabinet volume, sets the wattage. Estimate enclosure heat loss from three inputs: exposed surface area (m²), the temperature difference between your coldest ambient and desired internal minimum, and the enclosure's heat transfer coefficient (roughly 5.5 W/m²·K for uninsulated sheet steel; lower for insulated or plastic enclosures). Multiply them for required watts, then add margin.

Small, sealed, indoor panels: 25–50W (501025, 501050)
Mid-size or slightly exposed cabinets: 75–150W (501075, 501100, 501150)
Larger or outdoor enclosures with active circulation: 125–250W (801125, 801200, 503250)
High heat loss, large cabinets: 400–800W (801400, 801800, 503500, 503750)

Ratings here are quoted at a reference temperature (68°F for KH501, 50°F for KH800/KH503). Actual PTC output falls as surrounding air warms, which is by design. Size to your worst-case cold morning, not the average.

Electrical cabinet heater voltage and circuit matching

Confirm both voltage and current before you specify.

KH501 (25–150W): 110-240V AC/DC on every unit, so one part number covers most control-power situations, AC or DC.
KH800 panel-mount: voltage-specific. 125W, 400W, and 800W come in 115V; 125W, 200W, and 800W come in 230V. The 200W 230V draws ~1A (2A T fuse); the 400W 115V and 800W 230V draws ~3.6A (5A T fuse).
KH503 DIN-rail fan-assisted: 230V, 50/60 Hz only. 250W ≈ 1.2A, 500W ≈ 2.4A, 750W ≈ 3.6A.

Verify the branch circuit and fuse can carry the heater's rated current, and don't share a circuit that's already near capacity. A common ordering error is grabbing a 230V unit for a 115V panel. Check the KH800 model suffix (A33 = 115V, A44 = 230V) and remember all KH503 units are 230V only.

Mounting, clearance, and cabinet fan considerations

Mount the heater low in the enclosure so warm air rises past the components you're protecting. KH501 and KH503 clip to DIN rail; KH800 units are panel-mount aluminum housings.

Leave clearance around fan inlets and outlets (20 CFM on the 250W and 500W KH503, 26 CFM on the 750W). Blocked airflow trips overheat protection and shortens fan life.
Keep the heater away from wiring insulation, plastic ducting, and heat-sensitive components.
If you actually need cooling rather than heating, a cabinet heater is the wrong tool. Specify a filter fan or cabinet vent fan sized to your cooling load. Heating and cooling solve opposite problems; some outdoor enclosures need both, staged by thermostat and hygrostat.

Seifert cabinet heater range at a glance

Code	Series	Watts	Voltage	Fan / CFM	Thermostat	Mount
501025	KH501	25W	110-240V AC/DC	No	No (PTC)	DIN rail
501050	KH501	50W	110-240V AC/DC	No	No (PTC)	DIN rail
501075	KH501	75W	110-240V AC/DC	No	No (PTC)	DIN rail
501100	KH501	100W	110-240V AC/DC	No	No (PTC)	DIN rail
501150	KH501	150W	110-240V AC/DC	No	No (PTC)	DIN rail
801125A33000	KH800	125W	115V AC	Yes	Yes	Panel
801125A44000	KH800	125W	230V AC	Yes	Yes	Panel
801200A44000	KH800	200W	230V AC	Yes / 15.9	Yes	Panel
801400A33000	KH800	400W	115V AC	Yes / 25.9	Yes	Panel
503250	KH503	250W	230V AC	Yes / 20	No (PTC)	DIN rail
503500	KH503	500W	230V AC	Yes / 20	No (PTC)	DIN rail
503750	KH503	750W	230V AC	Yes / 26	No (PTC)	DIN rail

Common Mistakes (and the Fix)

✗ Sizing the heater to cabinet size instead of heat loss

✓ Calculate watts from surface area, worst-case temperature difference, and the enclosure heat transfer coefficient.

✗ Ordering a 230V KH800/KH503 for a 115V panel

✓ Check the model: KH800 A33 = 115V, A44 = 230V; all KH503 units are 230V only.

✗ Expecting the KH501 to hold a setpoint on its own

✓ Pair convective PTC heaters with a separate enclosure thermostat or hygrostat; KH800 has one built in.

✗ Blocking the fan inlet or outlet with wiring

✓ Keep 20–26 CFM air paths clear so airflow reaches components and overheat protection doesn't trip.

✗ Using a heater to fix a cooling problem

✓ For hot enclosures specify a filter fan or cabinet vent fan, not a heater.

✗ Mounting the heater at the top of the cabinet

✓ Mount low so rising warm air circulates upward past the protected components.

Frequently Asked Questions

How do I size a cabinet heater?

Calculate enclosure heat loss from exposed surface area, the temperature difference between minimum ambient and your target internal temperature, and the enclosure's heat transfer coefficient (roughly 5.5 W/m²·K for uninsulated sheet steel). Wattage ratings here are measured at 68°F (KH501) or 50°F (KH800/KH503), so match watts to your calculated loss, not just cabinet size. Undersizing leaves cold spots; oversizing wastes power. Size to your worst-case cold condition, not the average.

What is the difference between a convective and a fan cabinet heater?

Convective heaters like the KH501 rely on natural air movement across an aluminum radiator; quiet, no moving parts, good for small sealed enclosures. Fan-assisted units (KH503) and thermostat-fan units (KH800) force warm air around the cabinet, reducing cold spots in larger or densely packed panels. Fans add circulation but also a wear part.

Do these electrical cabinet heaters include a thermostat?

The KH800 panel-mount models (125W–800W) include an adjustable thermostat in Celsius and Fahrenheit plus a pilot light. The KH501 convective and KH503 fan-assisted units use self-regulating PTC elements and should be paired with a separate enclosure thermostat or hygrostat for setpoint control.

What is a self-regulating PTC heater?

A PTC (positive temperature coefficient) element increases resistance as it warms, so output drops automatically at higher surrounding temperatures. This limits surface temperature and power draw without a fixed-resistance coil, reducing overheating risk in confined panels.

115V or 230V: which cabinet heater voltage do I choose?

Match the heater to your control power. Every KH501 unit accepts 110-240V AC/DC. KH800 and KH503 are voltage-specific: order 115V (801125A33000, 801400A33000) or 230V (801125A44000, 801200A44000, 503250, 503500, 503750) to match your circuit. On the KH800, the model suffix tells you: A33 = 115V, A44 = 230V.

Where should I mount the heater in the cabinet?

Mount low in the enclosure so rising warm air circulates upward past components. Keep fan inlets and outlets clear of wiring and ducting, and leave clearance for airflow. The KH503 moves 20 CFM on the 250W/500W and 26 CFM on the 750W. Blocked airflow trips overheat protection.

Can I use a cabinet heater as an electrical cabinet fan for ventilation?

No. These are heaters with fans for warm-air circulation, not cooling vent fans. If your goal is exhausting hot air, you need a dedicated filter fan or cabinet vent fan sized to the enclosure's cooling load, not a heater. Heating and cooling solve opposite problems; some outdoor enclosures stage both by thermostat and hygrostat.

Terms Worth Knowing

PTC element: Positive temperature coefficient resistor whose resistance rises as it warms, self-limiting output and surface temperature.
Enclosure heat loss: Watts an enclosure sheds to colder ambient air; determines required heater wattage.
Convective heater: Heater that warms air by natural rising currents across a radiator, with no fan.
Fan-assisted heater: Heater with a fan that forces warm air through the cabinet to eliminate cold spots.
Condensation control: Keeping internal temperature above the dew point so moisture doesn't form on components.
IP20: Ingress rating protecting against fingers and objects over 12mm; no water protection.
Hygrostat: Humidity-sensing switch that turns a heater on when internal moisture rises.
CFM: Cubic feet per minute of airflow a heater's fan moves through the cabinet.

Written by the Products for Automation parts team · Last reviewed September 18, 2026 · Prices and stock on this page update live.