Short answer: a sealed enclosure sheds heat only through its walls, and the wall loss is Q = k·A·ΔT. Take a 16 x 12 x 10 in [406 x 305 x 254 mm] stainless box: 0.61 m² of wall at k = 3.7 W/m²K carries about 45 W for a 20 K rise at 25 C ambient. Feed the same box 100 W and the interior settles near 69 C, well past the 40 C ambient that most drive and supply datasheets assume. So count your watts before you seal the door, whether the seal is for sound or for washdown, and keep the load under what the walls carry.
What sealing does to the heat path
A vented enclosure cools with its air. Push 100 m³/h [59 cfm] through it at a 10 K air difference. With air at 1.2 kg/m³ and 1,005 J/kgK, that stream alone carries about 335 W out of the box. That is why a filtered fan keeps a bench cabinet cool.
Seal the door and that path closes. Every watt the parts keep making must now leave through the walls, as a mix of conduction, convection and radiation that one coefficient k sums up. For walls in still air the figure is 3.7 W/m²K for stainless, 5.5 W/m²K for painted steel and 3.5 W/m²K for plastic. The non-ventilated stainless sizing article turns the same arithmetic into a selection tool.
Two habits follow from the formula. An internal fan evens the air and steers heat toward the walls, yet it removes no heat itself, so it buys margin at your hot spots rather than watts of cooling. Spreading the hot parts along the backplate puts their losses onto more of the wall, and the layout article for sealed enclosures shows the arrangements that work. If your box already runs hot, start with the causes ranked in order. The article on why a driver box runs hot inside a sealed enclosure walks them with fixes.
The three numbers that set the capacity
The formula leaves you three inputs: wall area, wall material and the rise you accept. Area A is the whole outside surface, every face. The rise ΔT is inside air minus room air; with a shop at 25 C and devices happy to 40 C, you get to spend 15 K. Size electronics for 40 C (104 F) interior ambient, the figure most drive and power-supply datasheets assume unless their tables allow more.
| Wall material | k in still air | 16 x 12 x 10 in box, per kelvin of rise |
|---|---|---|
| Stainless | 3.7 W/m²K | 2.25 W |
| Painted steel | 5.5 W/m²K | 3.35 W |
| Plastic | 3.5 W/m²K | 2.13 W |
The coefficient counts radiation with conduction, which is why painted steel sheds half again as much as bare stainless at the same size. Each extra kelvin you accept adds 2.25 W to your budget on this box. Sun works the other way: it adds load, and the outdoor heat-gain article shows how to count solar watts. Plastic runs a shade below stainless at 3.5 W/m²K, and calculating internal temperature rise in sealed plastic enclosures works the same formula for non-metallic boxes.
Worked example: 16 x 12 x 10 in stainless box at 25 C
Run the arithmetic once and the box names its own watts:
- Area: 2 × (16 × 12) + 2 × (16 × 10) + 2 × (12 × 10) = 384 + 320 + 240 = 944 in² = 0.609 m².
- Per kelvin: 3.7 W/m²K × 0.609 m² = 2.25 W/K.
- Budget at 40 C inside and 25 C outside: 15 K × 2.25 W/K = 34 W.
- Check at a 30 W example load: 30 / 2.25 = 13.3 K, so the interior settles at 38 C. It passes.
- Caution at a 100 W example load: 100 / 2.25 = 44.4 K, so the interior reaches 25 + 44 = 69 C. That misses the 40 C rule by 29 K.
Wall area scales the watts one to one, so the next size up pays directly. A 20 x 16 x 12 in [508 x 406 x 305 mm] box has 1,504 in² = 0.970 m² of wall and 3.59 W/K of capacity: 54 W at the same 15 K, from 60% more wall. The caution case is a hands-on case too. ISO 13732-1 burn thresholds for bare metal sit near 60 C at 10 s of contact, so give a 69 C box switch-off time before you reach inside.
What sound insulation does to the same numbers
Sound wool is thermal wool. Stone wool conducts about 0.04 W/mK on typical datasheets, so a 25 mm [1 in] lining adds 0.025 / 0.04 = 0.625 m²K/W to the wall path's 1 / 3.7 = 0.27 m²K/W. The lined box totals 0.895 m²K/W, which drops the effective coefficient from 3.7 to about 1.1 W/m²K.
Run the worked box again with the lining in place:
- Capacity for the old 20 K rise: 20 / 0.895 = 22 W, against 45 W bare. About half the cooling went into the sound job.
- The old 34 W budget now costs 34 × 0.895 = 30 K of rise, so the interior lands near 55 C in a 25 C room, 15 K past the rule.
Placement is the fix. Leave one stretch of wall bare through the wool and bond the driver plate to it. A bare 500 x 500 mm [20 x 20 in] patch is 0.25 m², and it carries 3.7 × 0.25 × 15 = 14 W of your budget on its own. The sound-isolation enclosure article pairs wall build-up, door seals and heat control for cabinets like this. Getting sound out of an otherwise sealed box through a duct or baffle is the subject of the audible-alarm article on sealed enclosures.
How to budget the watts before you seal
Work in this order:
- List losses, not outputs. A 60 W supply at 85% efficiency delivering 50 W of load loses 50 / 0.85 - 50 = 9 W. Add each driver's dissipation and the controller's the same way.
- Fix the two temperatures: room air (25 C in the example) and interior limit (40 C unless a named datasheet allows more). The difference, 15 K here, is what you spend.
- Multiply the spendable rise by k·A: 15 K × 2.25 W/K = 34 W for the worked box.
- Compare your load list with the number. When it closes, seal it; when it does not, take the next line of the table.
| Load in the example box, bare walls, 25 C room | Interior settles near | Decision |
|---|---|---|
| up to 34 W | 40 C | Seal it; no cooling hardware needed |
| 34-45 W | 40-45 C | Look for a 50 C ambient rating in the device datasheets, or add wall area |
| 45-70 W | 45-56 C | Step up to 20 x 16 x 12 in walls (54 W at 15 K) or leave a 0.25 m² bare patch through any lining |
| over 70 W | 56 C and up | Move the driver box outside the sealed volume, or fit a sealed cooler rated to match the wall |
Anything mounted through the wall sets the assembly's rating at its own level; the weakest opening wins. Order a cooler whose rating matches the box, and fit it with the gasket its instructions call for. Once the cabinet runs, judge it by the air temperature at the hottest device after an hour at full load. The article on where to measure ambient temperature inside an enclosure shows where the probe belongs.
What to put on the order
If the budget closes at the size you have, order that box and keep every wall bare inside a lined cabinet. If it needs more wall, we build custom stainless to your width, height and depth from one piece. Place every cutout where the glands, cooler and display need it; the custom enclosure page takes the dimensions and the cutout list together. Custom work is delivered in 10 business days from your approval of the drawing.
Note the rating terms when you order. A stainless box from that catalog is rated NEMA 4X / IP66 by the manufacturer and not UL listed. The NEMA types grade water, dust and corrosion, never watts; no enclosure test measures the heat, so the wall arithmetic above is what you order against. The enclosure-types guide lays out what each type covers, and the enclosure selector shortlists by environment and inside size or carries your numbers to a quote.
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 |
|---|---|---|---|
| 16 × 12 × 10 in | 304 stainless | 16 x 12 x 10 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 |
| 24 × 20 × 8 in | 304 stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 30 × 24 × 10 in | 304 stainless | 30 x 24 x 10 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
How many watts can a sealed stainless enclosure carry?
Multiply the wall coefficient 3.7 W/m²K by the outside wall area and the rise you can spend. The 16 x 12 x 10 in example box has 0.61 m² of wall, so with a 25 C room and a 40 C interior limit it carries 3.7 x 0.609 x 15 = 34 W. Double the wall area and the watts double; spend 5 K more rise and the budget gains about 11 W.
How much cooling does a 25 mm lining of sound wool cost?
About half. Stone wool at 0.04 W/mK adds 0.025 / 0.04 = 0.625 m²K/W to the wall path's 0.27 m²K/W, so the effective coefficient falls from 3.7 to about 1.1 W/m²K and the example box drops from 45 W to about 22 W for a 20 K rise. A bare 0.25 m² patch left through the wool claws back roughly 14 W at a 15 K rise.
What interior temperature should a sealed enclosure be sized for?
Size for 40 C (104 F) inside unless a named datasheet allows more; that is the ambient most drive, PLC and power-supply tables assume. With a 25 C room the spendable rise is 15 K, worth 34 W on the example 16 x 12 x 10 in stainless box. Check the finished cabinet at the hottest device after an hour at full load.
Can a 100 W load live inside a sealed 16 x 12 x 10 in stainless box?
Only with active cooling. On walls alone it settles 100 / 2.25 = 44 K above the room, so at 25 C the interior sits near 69 C and misses a 40 C device rating by 29 K. A sealed cooler rated to match the wall, or a driver box outside the sealed volume, closes a budget that size.
Does an internal fan cool a sealed enclosure?
It evens the temperature and steers heat toward the walls, but it removes no heat itself: the wall area and the coefficient still set the loss. On the example box a fan spreads a corner-loaded driver's watts over the full 0.61 m² of wall, worth a few degrees at the hot spot. Budget to the walls first and treat the fan as spot relief.
