Enclosure heater vs desiccant: which stops condensation?

The short answer

An enclosure heater keeps the air inside a cabinet above its dew point for as long as it is powered. A desiccant removes water vapour from that air, powered or not. They fail in different situations: the heater fails when the power is off or the hygrostat is set wrong, the disposable desiccant fails when it is full. For a sealed enclosure under 100 litres that cycles between day and night, a self-regenerating desiccant does the job without energy or maintenance. For a large cabinet that must never freeze, the heater stays the right tool, sometimes alongside a passive desiccant.

This page compares four options on the same criteria: the anti-condensation heater with hygrostat, the silica gel sachet, the membrane breather vent, and the SRD sticker. So Sponge manufactures the last one; the method and sources are stated at the end.

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Why a sealed enclosure condenses at all

An IP65 or IP67 rating stops liquid water and dust. It does not stop water vapour. Every day/night cycle, the air inside the box warms, expands and pushes out through the seals; at night it cools, contracts and draws humid outside air back in. Over a season the internal air catches up with the outside humidity, and the first cold surface, a lens, a board, the lid, reaches its dew point. We described the mechanism in IP65 enclosures breathe: how moisture gets in and the physics in Dew point temperature.

Every anti-condensation device attacks one term of that equation: the heater raises the temperature so the dew point is never reached, the vent lets pressure equalise without a vacuum, the desiccant lowers the amount of water in the air.

Enclosure heater vs desiccant vs vent: the comparison table

Criterion	Anti-condensation heater + hygrostat	Silica gel sachet	Breather vent (membrane)	SRD sticker (AS-B)
Removes water vapour from the air	No	Yes, until saturated	No	Yes, continuously
Works with the enclosure unpowered	No	Yes	Yes	Yes
Power draw	10 to 150 W per unit (STEGO HG 140: 15 to 150 W; Pfannenberg FLH: 10 to 150 W)	0 W	0 W	0 W
Maintenance	Hygrostat setting and check	Replacement when saturated	None	None
Regeneration	Not applicable	In an oven, outside the enclosure	Not applicable	Spontaneous, inside the enclosure, at ambient temperature
Operating temperature	−45 to +70 °C (STEGO HG 140)	Wide	Wide (membrane dependent)	−20 to +70 °C
Typical enclosure volume	0.1 to several m³	Under 10 L	Any (pressure only)	0.5 to 100 L, one sticker per litre
Installation	DIN rail, wiring, hygrostat	Drop in	M12 or adhesive mount, hole in the wall	Self-adhesive, no tool
Adds heat inside the box	Yes	No	No	No
Unit cost (excl. VAT)	Heater plus hygrostat, plus wiring time	Under 1 €	A few euros	1.75 € per 50 × 20 mm sticker on a roll of 100

Data as of 28 September 2026. Heater figures from the STEGO HG 140 datasheet and the Pfannenberg FLH series pages; vent function as stated by GORE; sources listed at the end. Competitor columns describe the generic product type, not one reference.

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How an anti-condensation heater works, and where it stops

A cabinet heater is a resistive or PTC element, usually clipped on a DIN rail at the bottom of the enclosure, driven by a thermostat or a hygrostat. The two leading European ranges give the order of magnitude: STEGO’s HG 140 semiconductor heaters cover 15 to 150 W and are rated from −45 to +70 °C; Pfannenberg’s FLH radiant heaters cover 10 to 150 W and are sold, in the manufacturer’s words, “in combination with a thermostat or hygrostat, predominantly for the avoidance of excessively low temperatures or excessively high humidity in the control cabinet”.

The principle is sound: warmer air holds more water before it condenses, so raising the air a few degrees above the coldest surface keeps that surface dry. It works well in a switch cabinet that is powered all year, large enough to spread the heat, and serviced by people who can set the hygrostat.

It stops working in four common situations.

The enclosure is unpowered. A field box on a solar supply at the end of a winter night, an installation in storage before commissioning, a cabinet after a breaker trip: the heater is off exactly when the temperature drops fastest.
The hygrostat threshold is wrong for the site. Set too high, the heater runs after condensation has already formed; set too low, it runs permanently and the electricity bill follows.
The volume is small. Below a few litres a heater has no room, creates a hot spot next to the electronics and adds a thermal cycle of its own.
The water is still there. A heater does not remove a gram of water from the box. When it switches off, the same humid air cools again. It manages the symptom, every night, for the life of the equipment.

How a desiccant works inside an enclosure

A desiccant does the opposite: it takes water out of the air so that, when the box cools, there is not enough vapour left to condense. Three families exist, and they behave differently over time.

Silica gel sachets adsorb until full, then do nothing. In a sealed box that breathes with each cycle, a sachet sized for the volume lasts weeks to months depending on the leak rate and the climate, then has to be replaced or dried in an oven at 120 to 150 °C. We covered lifetimes and recharging in Reusable and rechargeable desiccants: which one really lasts. Their cost per unit is unbeatable; their cost per year on a hundred enclosures in the field is mostly labour.

Breather vents are not desiccants, but they are often bought for the same reason. GORE describes its protective vents as “equalizing pressures” and “reducing condensation”, the second by preventing pressure-driven ingress of liquid water through the seals. The vent does nothing to the water vapour already inside. In our climate chamber test of three identical IP66 boxes, the vented box still fogged on the 30 to 0 °C step; only the box fitted with the SRD sticker stayed clear. The test is documented in Gore-Tex vent vs SRD AS-B, and the vent’s real role in Gore Vent and breather vents. Vent and sticker are complementary: the vent handles pressure, the sticker handles residual moisture.

Self-regenerating desiccant (SRD) is a mesoporous alumina developed at Université Lyon 1 and bonded into a self-adhesive sticker. It adsorbs water above roughly 60 % relative humidity, with eight times the capacity of silica gel between 60 and 90 % RH, and releases it again during the warm phase of the cycle, inside the enclosure, without heating. The cycle repeats indefinitely: nothing to replace, nothing to power, −20 to +70 °C, REACH compliant, made in France. The material is described on the SRD material page.

What it costs over five years: one worked example

The numbers below are an illustration with stated assumptions, not a quotation. Adjust them to your site.

Assumptions: one 20-litre outdoor enclosure; a 30 W heater driven by a hygrostat that runs it 40 % of the time; electricity at the EU non-household average of 0.184 €/kWh (Eurostat, second half of 2025); silica gel replaced twice a year at a nominal 20 minutes of technician time per visit; AS-B sized at one sticker per litre.

Option	Year 1	Years 2 to 5	Five-year total
Heater 30 W at 40 % duty	Heater and hygrostat, wiring, plus 105 kWh ≈ 19 € of electricity	4 × 19 € ≈ 77 €	Hardware plus about 96 € of electricity, per enclosure
Silica gel sachets	2 sachets and 2 site visits	8 sachets and 8 site visits	Sachets are negligible; 10 visits of technician time are the real cost
AS-B stickers, 20 units	20 × 1.75 € = 35 €	0 €	35 €, no visit

The electricity line alone, 105 kWh a year for a single 30 W heater at 40 % duty, is what a fleet of a hundred enclosures turns into 10.5 MWh a year. The technician line is what makes silica gel expensive on remote sites. Run your own case with the sizing tool, which also estimates the yearly condensation risk for your climate.

When to choose which

Choose the heater when the enclosure is large, permanently powered, and must not freeze: control cabinets with mechanical relays, outdoor switchgear in continental winters, any equipment with a minimum operating temperature above the local winter. Add a hygrostat rather than a plain thermostat, and consider a passive desiccant alongside it to cover the unpowered hours.
Choose a passive desiccant when the enclosure is under 100 litres, when it may be unpowered, when nobody will come back to service it, or when the electronics cannot tolerate a hot spot: sensors, cameras, meters, telecom boxes, charging stations, agricultural robots. Between silica gel and SRD, the choice is the number of site visits you accept.
Choose a vent plus a desiccant when pressure cycling is severe (large temperature swings, altitude, wash-down): the vent protects the seals, the desiccant protects the electronics.
For volumes above one cubic metre, cabinets, shelters and containers, the sticker format is too small; the AS-C ribbon is the same material in a 200 × 8 cm strip, and can work next to a heater.

What the field says

Two validated cases are the closest to this question. On electric vehicle charging stations in service, over 85 winter days, the time spent in the condensation zone was divided by 2.6 with the passive ribbon, on equipment that already had its own thermal management. On a 0.6-litre IP67 camera enclosure, 48 hours in a climate chamber at −1 to +3 °C and 90 to 94 % RH left glass and optics dry with a single 10 cm² sticker. Both are documented, with protocol and results, on the validated use cases page. No customer is named there: the results are shared with the agreement of the engineering teams that ran them.

How we compared, and our position

So Sponge manufactures the AS-B sticker and the AS-C ribbon compared here. The heater figures come from public manufacturer documentation: the STEGO HG 140 datasheet (15 to 150 W, −45 to +70 °C) and the Pfannenberg FLH radiant heater pages (10 to 150 W, use with thermostat or hygrostat). The vent description is GORE’s own wording for its protective vents. The electricity price is the Eurostat EU non-household average for the second half of 2025. The five-year example uses assumptions stated in the text. Where a figure is generic to a product type rather than a specific reference, the table says so. This page will be revised when the manufacturers update their ranges.

Order AS-B online, from €100 excl. VAT

Sources

STEGO, Semiconductor heater HG 140 series, 15 W to 150 W, datasheet: farnell.com/datasheets/1674640.pdf
Pfannenberg, FLH radiant heaters 010 to 045 and FLH PTC radiant up to 150 W: pfannenberg.com, thermal management, heaters
W. L. Gore & Associates, GORE Protective Vents, adhesive series VE7, VE8, VE9: gore.com, protective adhesive vents for electronic outdoor enclosures
Eurostat, Electricity price statistics, non-household consumers, second half of 2025: ec.europa.eu/eurostat
So Sponge, climate chamber test of three IP66 enclosures and validated use cases: pages linked above