Enclosure heat calculator
This enclosure heat calculator works out how much heat a sealed enclosure can dissipate and how hot it runs inside. Pick one of our sizes or enter your own, say how it is mounted and what it is made of, then enter the heat inside, the hottest ambient and the highest temperature your equipment allows. It gives the effective surface and the temperature rise and, when the walls are not enough, the heat exchanger, air conditioner or fan the load needs. The formulas and a worked example are below.
Result
Enter the size, the heat inside and both temperatures.
Sealed looks sufficient on this estimate: about 60 °C inside at 35 °C ambient, – under your limit. Allow for sun, still air and parts added later.
Marginal: sealed, about 60 °C inside at 35 °C ambient, right at your 45 °C limit. Allow for sun, still air and parts added later, and plan a small air-to-air heat exchanger or a larger size.
44.5 W more than the walls shed at your 45 °C limit: sealed, it would reach about 60 °C.
- Air-to-air heat exchanger (closed loop, keeps the seal): at least 4.4 W/K (2.47 W/°F). It works only while the air outside is cooler than the inside.
- Enclosure air conditioner (closed loop, keeps the seal): at least 44.5 W of cooling.
- Fan and filter (open loop): about 23 m³/h (13 CFM) at sea level. It brings outside air in, so the enclosure is no longer NEMA 4X unless the fan unit itself is rated 4X.
- A larger size: the smallest of our stainless wall-mount sizes that sheds this load sealed is 42 × 36 × 8 in.
- A larger size: none of our standard sizes sheds this load sealed; a custom size with more surface, or cooling.
- Or move a heat source, such as a power supply, outside the enclosure.
Ambient is at or above your limit, so only a closed-loop air conditioner can hold it: at least 44.5 W (the 74.1 W inside plus – coming in through the walls).
- Effective surface, A
- 0.801 m² (8.62 ft²)
- Heat transfer, k × A
- 2.96 W/K
- Design heat load
- 74.1 W
- Temperature rise, sealed
- 25.0 K (45.0 °F)
- Inside, sealed
- 60 °C / 140 °F
- Walls shed at your limit
- 29.6 W
- Surface needed to stay sealed
- 2.00 m²
- With the lowest published k
- k = 1.94 W/m²K: rise 47.7 K
An estimate, not a rating: still air, no sun, one average inside temperature. Choose cooling with margin and from the cooling unit maker's data.
How it calculates
The formulas, in plain sight
| Step | Formula | Notes |
|---|---|---|
| Effective surface, wall-mounted | A = 1.4 · W · (H + D) + 1.8 · D · H | IEC/TR 60890, a single enclosure on a wall: the back sheds nothing. |
| Effective surface, exposed on all sides | A = 1.8 · H · (W + D) + 1.4 · W · D | On an arm, a pedestal or free-standing. H, W and D in metres. |
| Heat the walls shed | Q = k · A · ΔT | ΔT = inside air minus outside air, in K (the same as a °C difference). |
| Temperature rise, sealed | ΔT = Q / (k · A) | Inside temperature = ambient + ΔT. |
| Air-to-air heat exchanger | qw = (Q − k · A · ΔT) / ΔT | Specific output in W/K; only while the outside air is cooler than the inside. |
| Enclosure air conditioner | QK = Q − k · A · (Ti − Ta) | Cooling output in W; when the room is hotter than the inside, the walls add heat. |
| Fan and filter | V = 3.1 · Q / ΔT (m³/h) · CFM = 3.16 · Q / ΔT(°F) | Factor 3.1 up to 100 m altitude, 3.5 at 750–1,000 m; ignores the walls, so it errs high. |
| Material | k used here | Lowest published value |
|---|---|---|
| Stainless steel, unpainted | 3.7 W/m²K | 1.94 W/m²K |
| Painted sheet steel | 5.5 W/m²K | 4.26 W/m²K |
| Plastic or non-metallic | 3.5 W/m²K | Same |
Published coefficients for unpainted stainless differ by about a factor of two, because bare stainless radiates heat less well than paint. The calculator uses 3.7 W/m²K, as our product pages do, and shows the rise with the lowest published value as a check. Where each number comes from.
Worked example
24 × 20 × 8 in, 74.1 W, 35 °C room, 45 °C limit
- Heat load. The heat guide's example panel loses 59.3 W (power supply, PLC, switch, small PC, relays). With the 25% margin:
59.3 × 1.25 = 74.1 W. - Allowed rise. The lowest-rated device allows 50 °C; we design for 45 °C inside on a 35 °C day:
ΔT = 45 − 35 = 10 K(18 °F). - Effective surface. The 24 × 20 × 8 in enclosure on a wall, H, W, D = 0.610, 0.508, 0.203 m:
A = 1.4 × 0.508 × (0.610 + 0.203) + 1.8 × 0.203 × 0.610 = 0.801 m². - What the walls shed.
k × A = 3.7 × 0.801 = 2.96 W/K; at the allowed rise,2.96 × 10 = 29.6 W. - Sealed, it would reach.
ΔT = 74.1 / 2.96 = 25.0 K, so about 60 °C inside: above the limit, 44.5 W more than the walls shed. - Cooling. Heat exchanger:
(74.1 − 29.6) / 10 = 4.4 W/K. Air conditioner holding 45 °C: at least 44.5 W; holding 35 °C inside in a 45 °C room:74.1 + 2.96 × 10 = 104 W. Fan and filter:3.1 × 74.1 / 10 = 23 m³/h(13 CFM), open loop. - Or a larger size. To stay sealed the walls need
A = 74.1 / (3.7 × 10) = 2.00 m², 2.5 times this enclosure. The smallest of our sizes with that much surface is the 42 × 36 × 8 in (2.02 m²).
The heat calculation guide works the same example with the plain surface area (0.764 m², the five faces that are not against the wall); the IEC/TR 60890 surface used here and on the product pages gives 0.801 m², within 5%.
Assumptions
What the numbers assume
- Steady state, still air, indoors, no sun. Outdoors, add the solar gain to the heat load: the heat guide shows how, and the outdoor guide covers shields and finishes.
- One average inside temperature. A device that produces much of the heat, or sits next to one, runs hotter: measure near the hottest devices.
- Sealed: no vents or openings. The fan line is the open-loop alternative, and it ends a NEMA 4X rating unless the fan unit is rated 4X.
- k from enclosure climate-control catalogues; the lower check value from a heat exchanger selection guide. Bare aluminum is not offered: its published coefficients disagree widely, so ask the enclosure maker.
- One enclosure on its own, on a wall or exposed on all sides. Enclosures bolted side by side shed less, and IEC/TR 60890 has its own factors for them.
- No safety margin unless you tick it; one enclosure maker's thermal guide recommends 25% for critical applications.
- An estimate, not a rating. Choose cooling units with margin, from their maker's data, and with the enclosure's type rating.
By size
Heat our sizes shed sealed
| Size | Effective surface | Shed on a wall, 10 K | Shed on a wall, 20 K | Shed exposed on all sides, 10 K |
|---|---|---|---|---|
| 12 × 10 × 6 in | 0.25 m² | ≈ 9 W | ≈ 18 W | ≈ 10 W |
| 16 × 12 × 8 in | 0.41 m² | ≈ 15 W | ≈ 30 W | ≈ 17 W |
| 20 × 16 × 8 in | 0.59 m² | ≈ 22 W | ≈ 44 W | ≈ 25 W |
| 24 × 20 × 8 in | 0.80 m² | ≈ 30 W | ≈ 59 W | ≈ 34 W |
| 30 × 24 × 10 in | 1.22 m² | ≈ 45 W | ≈ 90 W | ≈ 52 W |
| 36 × 30 × 12 in | 1.80 m² | ≈ 67 W | ≈ 133 W | ≈ 77 W |
| 10.1" HMI housing on an arm | 0.20 m² | – | – | ≈ 8 W |
| 15.6" HMI housing on an arm | 0.36 m² | – | – | ≈ 13 W |
| 21.5" HMI housing on an arm | 0.54 m² | – | – | ≈ 20 W |
Every size, with its inside, panel and depth: the enclosure size chart.
Guide
Heat calculation
Heat load, allowed temperature rise, surface-area dissipation, solar gain and cooling sizing, worked through one enclosure with the arithmetic shown.
Read the guideGuide
Condensation
Dew point table, why sealed boxes breathe, heater sizing with a worked example, rated vent drains, desiccant and air conditioner condensate.
Read the guideGuide
Outdoor enclosures
Which NEMA type for rain, hose and salt, how much heat the sun adds, colour and sun shields, cold nights, UV and mounting.
Read the guideGuide
Sizing an enclosure
Component envelope, mounting panel, spare space, wire bending room, depth, heat and door clearance, with a worked example and CAD.
Read the guideNot a standard size?
Your size, material and cutouts, delivered in 10 business days.
Set width, height and depth, the material and the NEMA type in the enclosure builder, or send your drawing. From one piece, anywhere in the world. Counted from your order; for custom work, from your approval of the drawing.
Asked and answered
Enclosure heat calculator: questions
How do I calculate enclosure heat dissipation?
Multiply the heat transfer coefficient k by the effective surface A and the allowed temperature rise: Q = k × A × ΔT. A 24 × 20 × 8 in stainless enclosure on a wall has A = 0.801 m², so at k = 3.7 W/m²K and a 10 K rise it sheds about 30 W.
How do I calculate the temperature rise inside an enclosure?
Divide the heat load by k × A: ΔT = Q / (k × A). 74.1 W in that enclosure gives 74.1 / 2.96 = 25 K, so about 60 °C inside on a 35 °C day.
Which heat transfer coefficient should I use for stainless steel?
Published values for unpainted stainless differ: enclosure climate-control catalogues give about 3.7 W/m²K, one heat exchanger selection guide about 1.94. Both are lower than painted steel (about 5.5), because bare stainless radiates heat less well than paint. The calculator uses 3.7, as our product pages do, and shows the rise with 1.94 as a check.
Does mounting change how much heat an enclosure sheds?
Yes. On a wall the back sheds nothing; exposed on all sides, the same enclosure has more effective surface. For the 24 × 20 × 8 in enclosure, IEC/TR 60890 gives 0.801 m² on a wall and 0.925 m² exposed on all sides.
When does a sealed enclosure need a heat exchanger or an air conditioner?
When the walls cannot shed the load at the rise you can allow. A heat exchanger keeps the enclosure sealed but only works while the outside air is cooler than the inside; an air conditioner can hold the inside below ambient. A fan and filter is cheaper but open loop: the enclosure is no longer NEMA 4X unless the fan unit is rated 4X.
