# Is there a "rule of thumb" for power dissipation of an enclosed circuit to help determine when to do a thorough analysis?

I'm starting a project and the electronics will be enclosed in a wood sign outside. Even though it's shaded, I'm concerned about heat buildup in the summer. Is there some rule of thumb that says if your total power dissipation is below nnn mW, you'll have no issues with heat buildup?

To put it another way: If your circuit dissipates 100 uW, do you worry about heat buildup? No. What about 10 mW? I'm guessing probably not. What about 100 mW? Maybe, maybe not (I really don't know). At some point the power dissipation gets high enough where you decide it needs closer examination. Where is that? This is what I'm after.

FYI, I found this calculator and would like to verify its correctness. I could also use the answer to this question to help check it.

• For knowing how much the temperature will be inside the enclosure, we'd have to know how much it dissipates, and for that we need some numbers, such as how much heat is generated and what is your target maximum temperature inside the enclosure and the ambient temperature outside the enclosure it must operate in. Commented Oct 13, 2021 at 20:44
• In consideration should be taken power dissipation, volume of enclosure, thermocondactivity of the enclosure walls, ambient temperature. You can set the fan and thermostat for case. Commented Oct 13, 2021 at 20:55
• Using the linked calculator seems like a good plan.
– user80875
Commented Oct 13, 2021 at 21:50
• Justme and user263983--are you saying there is no general "rule of thumb" that says if total power dissipation is lower than "n", there's no (substantial) heat gain and you don't need to worry about it? In other words, it sounds like you're saying you always need to calculate it. Thanks. Commented Oct 13, 2021 at 22:12
• Charles, I found that calculator awhile back and forgot about it. As I was typing this question, I remembered it and realized that maybe I can use any info gained here to verify/validate it. Thanks. Commented Oct 13, 2021 at 22:14