Short answer: a food-storage tub works only in shade, only at low power, and only for a few seasons. On a roof in full sun, a 12 x 8 x 4 in [305 x 203 x 102 mm] tub carrying a PoE gateway reaches about 65 C [149 F] inside at 35 C [95 F] air — 25 K over the 40 C [104 F] that most industrial electronics is rated for. The snap lid holds no rating, the plastic chalks in UV, and the cable hole you cut is where the water arrives. Keep the tub for your shaded, temporary node; for anything permanent, order a UV-stable polycarbonate or 304 stainless enclosure with glands on the bottom face, delivered in 10 business days.
Will a plastic storage box keep water out on a roof?
It sheds rain for a season or two, but it holds no rating of any kind, and it leaks where you cut the hole rather than at the lid: plan on the cable entry being the wet point, with the lid seam a distant second.
A tub seals by a molded lip under interference. There is no gasket and no latch compression, so a lid that warps 1 mm in the sun opens a capillary path for wind-driven rain, and roofs see plenty of that in 40 to 60 km/h gusts. What keeps a tub dry is the entry: cut low on a side wall, snug to the cable, sealed with neutral-cure silicone, and hang a 50 mm [2 in] drip loop below it so water running down the cable drops off before the hole.
On a rated box you do the same job with a gland. A 1/2 in NPT or M12 gland with a 3 to 6.5 mm seal range takes a Cat 5e or antenna cable, and the field-cut hole then carries the gland's rating instead of being a leak. The assembly is only as good as its weakest part, so the gland sets what the whole box survives. The entry is where most outdoor boxes take water, which is why sealing an outdoor junction box starts with glands and drip loops rather than a thicker door.
Sealing an outdoor junction box: glands, drip loops and drains shows the entry details that keep a rated box at its rating.
How hot does a sealed plastic box get in full sun?
About 65 C inside at 35 C air for a 12 x 8 x 4 in tub with the gateway running: the sun supplies roughly three quarters of the heat, so efficiency in your circuit barely moves the number.
Run the arithmetic for a typical roof node:
- Surface area: 2 × (12 × 8 + 12 × 4 + 8 × 4) = 352 in², or 0.23 m².
- Wall heat transfer: plastic runs k = 3.5 W/m²K in our thermal guides, so the tub sheds 3.5 × 0.23 = 0.8 W for every kelvin of rise.
- Electronics: budget the node's full draw as heat; a PoE gateway draws about 5 W.
- Sun: clear midday sun delivers about 1000 W/m², the same peak used to rate solar panels, and the 12 x 8 in lid catches 0.06 m² of it. About 30 percent ends up trapped as heat — the translucent lid passes light onto the dark board, the curved surface reflects the rest — which is 0.06 × 1000 × 0.3 ≈ 19 W.
- Total heat: 5 + 19 = 24 W. Rise: 24 / 0.8 = 30 K. Inside: 35 + 30 = 65 C.
Drives and most industrial electronics are rated for 40 C ambient unless the datasheet says more, so you sit 25 K over the limit on an ordinary summer afternoon. Move the same tub into full shade and the 19 W disappears: 5 / 0.8 = 6 K of rise, so 41 C at 35 C air and 36 C at 30 C air. Shade is the biggest lever you have, worth more than any material swap — cooling a dark outdoor enclosure in full sun works the same arithmetic from the paint side.
What about condensation inside the tub at night?
Count on it: air sealed in at 30 C and 60 percent relative humidity has a dew point near 21 C, and a lid under a clear sky runs up to 5 K colder than the night air, so water forms on it and drips.
The snap seal is no vapor barrier, so the tub breathes daily — warm humid air moves in as the box cools, and every cycle reloads it with water. Three habits keep your node dry: mount the board vertical with terminals at the bottom so a lid drip runs past it; keep the electronics powered, since that steady draw holds the interior air above the lid temperature all night; and put the cable entry low so pooled water never touches a live terminal. On a rated enclosure you can add a breather drain instead, with its own stated rating — the assembly then drops to that rating, which suits a sheltered wall better than driven rain. Enclosure vent or sealed box: which stays dry outdoors compares the two approaches honestly.
How long does a plastic tub last in UV before it cracks?
One to three roof summers: unstabilized polypropylene chalks, embrittles and cracks through in that band per the outdoor-aging data plastics suppliers publish, and the first frost finishes what the sun starts.
UV-stabilized polycarbonate is the plastic built for this job; capped sheet datasheets state about 10 years of outdoor life. Your tub has neither the stabilizer package nor the cap layer, and the same radiation takes the spring out of the lid lip as well. If you stay with plastic, buy a box sold as UV-stable with a stated outdoor life on its datasheet. Polycarbonate versus fiberglass enclosures covers what each polymer tolerates and where each one wins.
Is a metal enclosure cooler than a plastic one?
Barely: plastic sheds 3.5 W/m²K and stainless 3.7 W/m²K, so the same 24 W in the same footprint gives a 30 K rise in plastic and 29 K in stainless — one kelvin of difference, not a fix.
The wall material is not the bottleneck. The thin air films on both surfaces are, which is why every solid wall lands in the same narrow band; paint wins on emissivity, not on thickness.
| Wall | k, W/m²K | Rise with 24 W in 0.23 m² | Inside at 35 C air |
|---|---|---|---|
| Translucent plastic tub | 3.5 | 30 K | 65 C |
| Brushed stainless | 3.7 | 29 K | 64 C |
| Painted steel, light grey | 5.5 | 19 K | 54 C |
Color moves the number far more than material does. A white opaque box absorbs about 20 percent of the sun instead of 30, so the tub painted white carries 17 W total, rises 21 K and lands at 56 C — still over the limit. No plain box wins direct midday sun: a white 16 x 16 x 12 in painted box works out to 43 C at 35 C air. The fixes that work remove the beam — a shaded wall, an eave, or a light shield plate mounted 50 to 100 mm [2 to 4 in] above the box with open edges, which leaves only the diffuse share and lands you at 39 to 44 C.
What rating does the replacement box need?
IP66, or a NEMA 4X-type rating in a US specification: the roof supplies rain, wind-driven spray, dust and years of sun, and IP66's 12.5 mm nozzle at 100 L/min leaves real margin over weather.
IEC 60529 tests the second digit 6 with a 12.5 mm nozzle at 100 L/min; IP65 stops at a 6.3 mm nozzle at 12.5 L/min. A wall-mounted node above the eave rarely needs more: IP66 is a jet rating, not immersion, and standing water is what pushes you to the 1 m, 30 min test of IP67. In US installations, NEC 110.28 is explicit that an IP rating is not a substitute for an enclosure type rating, so write the type into your spec. On this site the ratings are manufacturer ratings — rated NEMA 4X / IP66 by the manufacturer; not UL listed — and NEMA itself tests nothing; it publishes the type definitions, and listing to UL 50E is a separate evaluation. The rating belongs to the whole assembly: gland, window and breather are parts of it, and the lowest part sets the result. The IP rating chart maps every digit to its test.
What should you order instead of the tub?
A UV-stable polycarbonate or 304 stainless enclosure, sized from the heat arithmetic above, with glands on the bottom face and a light finish: in shade, a box with about 0.33 m² of surface (a 12 x 10 x 6 in shape) holds the node at 39 C in 35 C air.
| Where the node sits | What to order | Inside temperature at 5 W |
|---|---|---|
| Shaded wall, temporary test node | Keep the tub one season: low side entry, 50 mm drip loop, neutral-cure silicone; swap it when it chalks | 41 C at 35 C air |
| Shaded wall, permanent | 304 stainless wall-mount or UV-stable polycarbonate, manufacturer-rated NEMA 4X-type / IP66, glands on the bottom face | 36 to 39 C |
| Full sun, shield possible | The same box plus a light shield plate 50 to 100 mm above it, open at the edges | 39 to 44 C |
| Full sun, no shield | Move the electronics into the stairwell and run cable to a roof antenna | Room temperature |
You set material, height, width, depth and every cutout on a custom enclosure, built from one piece and delivered in 10 business days counted from your approval of the drawing; polycarbonate and fiberglass come in standard molded sizes cut to your layout. The catalog stainless lines run from 6 x 4 x 4 in to 60 x 36 x 16 in (H x W x D), every one hinged with a gasketed door and a removable mounting panel — browse them in the stainless size finder. Near the coast, take 316L: 304 pits under salt deposits even at room temperature, and molybdenum is what resists it, as corrosion prevention inside an outdoor stainless enclosure lays out. For a roof-mounted radio node in particular, putting an indoor LoRaWAN gateway in an outdoor enclosure walks the whole build.
Catalog dimensions to compare
Compare these catalog dimensions with your component layout. Open each enclosure for its rating, material and usable space, then check those specifications against your application.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 12 × 8 in | 304 stainless | 16 x 12 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 304 stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 24 × 20 × 8 in | 304 stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
How many watts can a sealed plastic tub dissipate in the shade?
A 12 x 8 x 4 in tub has 0.23 m² of surface and sheds heat at 3.5 W/m²K, so it dissipates about 0.8 W for every kelvin of rise. That is 8 W per 10 K: at 30 C air the board sits near 36 C, and at 35 C air it sits near 41 C. Stay at or under that draw in shade, or move to a box with more surface.
Can a plastic box actually warp or melt in sunshine?
Yes, without ever reaching a melting point. A dark lid in full sun runs 30 to 40 K above air temperature, so 70 to 80 C on a 40 C day. Polypropylene distorts from about 100 C under light load, and hot electronics inside push a dark case over that line. The sun load plus the circuit does it, not the air alone.
Can I leave the box in the stairwell and only the antenna on the roof?
Yes, and it is often the cheapest reliable fix. PoE carries power and data 100 m over one Cat 5e run, so a shaded indoor box feeding an outdoor antenna on the roof beats almost any enclosure sitting in the sun. Keep the antenna cable short and sealed at its connector, and your electronics spend the year near room temperature.
Does a silica gel sachet stop condensation in the tub?
It buys time, not a fix. A 10 g sachet holds about 3 g of water at high humidity, and the air in a 7 L tub carries well under a gram of vapor per daily cycle. In a truly vapor-tight box that sachet lasts for years; through a breathing snap lid it loads up in weeks. Keep the board powered and vertical, with the drip path pointed away from it.
Should I drill vent holes in the tub to let heat out?
Vents bring the inside to within 2 to 3 K of ambient for that load, but they trade away the seal: dust and wind-driven rain come straight in. Use them only on a sheltered wall, with the holes on the bottom face and cover above. On a rated enclosure, a breather drain with a stated rating does the same job without an open hole.
