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Hot (and Cold) Attic Tempertures and Electronic Equipment

An unfinished attic can be an extreme environment for electronic equipment, with conditions that are very unlike what is experienced inside normal living spaces. What's the deal with installing electronic equipment in an unfinished and uninsulated attic?

Attic Space
 

I wanted to install a standard WiFi router in my attic to function as a Wireless ISP (WISP) gateway. My attic is a fantastic location from a radio signal perspective, but it is an uncomfortable place for both people and electronic gear. Although the attic is well insulated, that insulation is on the floor, designed to keep the living space of my home at moderate temperatures. As a WISP gateway, my WiFi router is best mounted above the insulation and close to the roof, where the only protection from weather extremes is the wood of the roof and a layer of asphalt shingles.

Equipment Specifications and Extremes

Almost all electronic equipment has a set of specifications regarding operating environment. These specifications state the conditions required for reliable operation. These specs are ignored by most people, because most equipment is designed to work alongside people. But if you're installing equipment in an unfinished attic, crawl space, shed, or garage, these specifications may become critical.

Why can't all electronic equipment withstand a huge range of conditions? Generally it is due to cost. Some electronic components may misbehave when temperatures fall below or rise above a specific threshold. For example, a display panel, battery, or capacitor that contains some liquid can behave very differently if that liquid freezes, or if that liquid turns to vapor. Similarly, very high humidity can alter circuit resistance. The impact of the environment on electronic gear can be significant.  Conditions outside of the norm of  needs some thought.

The Attic Environment

So what are the details of the environment in my attic, and is it compatible with my equipment?

Attic Protection

The attic, being a hat for a home, is designed to keep rain and snow and pests out. My home has asphalt shingles that do a great job of weather protection. I do not expect to see any rain or snow inside the attic area at all, ever. It should be dry 365 days a year.

My attic has some passive air vents. There is a ridge vent along the top of the roof line, and there are larger air vents located at the gables. These vents should help keep attic temperatures somewhat similar to outdoor temperatures, but more on that later.

All the vents are screened, and there are no (known) holes in the attic, so I do not expect any rodents, birds, or insects in there. Nobody needs those pests, and that includes electronic equipment. That said, some insects may find their way inside, so there is a bit of a risk that insects may crawl into equipment to find warmth.

Attic Potential for Cold

Since my attic is vented, its temperature will somewhat follow the temperature of the outdoor air. And where I live, it can get pretty darn cold.

By using the Monthly Summarized Data report from NOAA, I found that within the past 20+ years my area has been as cold as -25 °C. That's very cold, but I think my attic temperatures will always be warmer than that for several reasons.

  • I suspect that attic temperatures will always be a bit warmer than the outside air, as there will always be some heat leakage up into the attic from the living space below. 
  • The minimal temperature of -25 °C is the lowest temperature on record.  It could have been that cold for just a few minutes.  My attic may be a little more more moderate, as the heat of my attic wouldn't leak out instantly.
  • Given recent global warming predictions, my area is getting quite a bit warmer in the winter.  It is still possible for some crazy cold temperatures, but it is generally less likely.  The odds of  "-25 °C" might have happened once every 20 years.  Now the odds might be once every 100 years.

For the sake of being conservative, I'll put a stake in the ground and say that my worst case attic cold temperature will be -25 °C, although I imagine that -15 °C might be closer to a realistic minimum.

The Hot Attic may be extreme

Again, according to NOAA, the outside summer air in my region has been as warm as +40 °C.   That's pretty crazy.  But my house is covered with shingles and gets a lot of direct sunlight, so it will be even crazier. I guess that potential of the sun beating down on the roof on a sunny day, could induce the attic to get as warm as perhaps +50 °C. Hopefully when the weather is so hot, it will also be hazy, reducing some of the solar radiation heating the roof.  Stronger outdoor winds could help push some of the hot air out through the venting system.

All things considered, I will again use my conservative hat and use +50 °C as the highest temperature I'll see inside the attic.

Measurement

All my temperature scenarios are just estimates based on historic weather data. So what will it really be like up there? 

Onvis Temperature Sensor

 

I have placed a Homekit-based Onvis temperature sensor in my attic. The Onvis allows me to monitor and record temperature over time. So far, the attic temperature has peaked at 47 °C, on calm and sunny early summer  day where outdoor temperatures peaked at 36 °C. Therefore, when the weather is right, the attic has been +11 °C above outdoor temperatures. I'll be watching temperatures closely as we go through summer.

Gear Selection based on Operating Environment

The vast majority of higher-end gear is designed to operate somewhere between 0 °C and 40 °C, but I  expect to regularly see temperatures ranging from -15 °C and 50 °C, with a worst-case range of -25 °C to +55 °C.  Most equipment will fail in short order with those crazy temperatures.

Therefore I have chosen the MikroTik hAP AC lite router, which can operate between -30 °C and +70 °C. The odds of the temperature of my attic being outside of that range is vanishingly small.  It is important to note that the router will be "on" 24x365, so there will always be some heat generated inside the unit.  Therefore, I think the most significant challenge will be the high temperatures of summer.

I have the MikroTik attached to an active PoE switch, so I will be using it with an active PoE splitter.  The splitter's [poorly noted and perhaps untrustworthy] specs suggest an operational range between -30 °C to +80 °C.

Note that the previously mentioned Onvis sensor will be operating in an environment that is outside of its specifications (-10°C to +45 °C), so I might end up changing my temperature monitoring strategy.  In the least, may end up using lithium batteries within the Onvis because Lithium batteries can better deal with  temperature extremes (often -40 °C to +60 °C) compared with alkaline batteries (-18°C to 55°C) .

The Specifications and the Data

I'll periodically update the following data. 

Recorded Temperature Extremes (so far)

Max Attic Temperature (Sensor): +47 °C
 Outdoor Temperature..........: +36 °C (Δ: +11 °C)

Min Attic Temperature (Sensor): +06 °C
 Outdoor Temperature..........: +05 °C (Δ: +1 °C)

Equipment  Specifications

Equipment at high risk of operating outside of specification is in bold.
Equipment operated outside of temperature specifications are in red.
 
Expected Extremes...: -25 °C to +50 °C 
Current Extremes....: +06 °C to +47 °C

MikroTik hAP AC lite: -30 °C to +70 °C
Active PoE Splitter.: -30 °C to +80 °C
ONVIS Sensor........: -10 °C to +45 °C
Alkaline batteries..: -18 °C to +55 °C
Lithium batteries...: -40 °C to +60 °C (not yet in use)
 

"Can you show temperatures in Freedom Units?"

Specifications for engineered equipment is generally presented in degrees Celsius.  It's just easier to stick with the industry norm instead of converting back and forth.  If you don't understand Celsius, Google can translate it for you.

Just as a simple recap, from the human livability perspective:

  • ☀️ 45 °C is super hot
  • ☀️ 35 °C is very hot
  • ☀️ 30 °C is hot  (turn on the A/C)
  • ✓  25 °C is warm
  • ✓  20 °C is comfortable
  • ❅  15 °C is cool (turn on the heat)
  • ❅  10 °C is cold
  • ❅   0 °C is freezing

 Adjust for your regional tastes.

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