Effect of room temp on your CPU load temps

[graysky]

I was curious just how much room temperature can affect the temperature of the PC. I chose to look at the CPU since Speedfan can monitor and log temps for each of the 4 cores in my Q6600, and since of all the components, the CPU is probably the most sensitive to changes in air temp. since mine is air cooled.

Anyway, I did the same x264.exe encode that I have been doing for all my temperature comparisons and monitored room temp. with a calibrated digital thermometer at several points during each encode. These were averaged and graphed against the averaged reported core temp* values from Speedfan for the entire second pass of a 2-pass x264 encode of the same video file. I was happy to see that for the different room temps used, the increases were pretty linear (certainly within error).

Result:
You can see by the slopes of the regression line that every delta °F of room temp. affected the average core temp by about 0.8 °C and for your Celsius folks, every delta °C of room temp. affected the average core temp by about 1-1/2 °C.

So what does this mean and why do you care? Well, using these rules of thumb, if it's currently 70 °F in your room, and your average load core temp is 65 °C, you can expect that to change by roughly 0.8 °C for every single °F your room temp. change. Say your room hits 80 °F. Your load core temp should increase from 65 to 73 °C which may be unacceptable to you and you might want to adjust your o/c accordingly. This is just an approximation based on my system. Your mileage may vary...

*The numbers I used are equivalent to those collected by TAT or RMClock: these temps are core temps. As I understand it, TJunction never changes and is a fixed value for a given chip. The Quads get a values of 100 °C and the duals get 85 °C. The core temp is defined as:

Coretemp = TJunction - DTS

Example, DTS reads 62. You take 100-62=38 and your coretemp is 38 °C.

DTS (Digital Thermal Sensor) can be read directly for each core. See this thread for more on reading your DTS directly without software like TAT or RMClock paying attention to uncleweb's posts using crystalCPUID to read the DTS directly. When I tried this method, I was able to get the same values for the core temps on my Q6600 as TAT and RMClock gave me. For some reason, Speedfan always shows cooler core temps for my chip which I corrected by adding constants to the data. Read more about that in the caption under the graph.

Raw data and graphs
Hardware specs: Q6600 (lapped) @ 9x333, Ultra-120 Extreme (lapped), P5B-Del., P182 case w/ 4 fans on low, Corsair 620HX, Ballistix DDR2-800 @ 4-4-4-12 (1:1 Mem:CPU).

Graph
Data table

Downloads and References
To download crystalCPUID
To download rmclock
To download speedfan
To download TAT

<b">To read more about TJunction and for a discussion about other things relating to thermal output from C2D chips

[txtmstrjoe]

Very helpful information, sir. I printed out a copy of each graph and the table just to have a better look (I seem to respond better to reading hard copies!)

Thank you very much for posting.

[f1r3s1d3]

It's pretty much common sense. As ambient warms, so will everything else.. 1:1.

I guess this clears it up for some people though.

[graysky]

Glad someone else is finding this useful -- always glad to contribute.

[CurseTheSky]

Originally posted by: f1r3s1d3
It's pretty much common sense. As ambient warms, so will everything else.. 1:1.

I guess this clears it up for some people though.

Result: Every delta °C of room temp. affected the average tcase by about 1.9 °C. So a good rule of thumb is: for every 1 °C the room temp. changes, the load CPU temps should change by about 2 °C.

It's really not 1:1. During the winter, I'd estimate that my room can drop down to the low-to-mid 60s, with TAT temps of ~32C idle / 45C load. During the summer, it probably reaches high 70s to low 80s in here, and the processor spikes to 40-45C idle, and 55C load.

It also depends HIGHLY on the room's ventilation, your case ventilation, surrounding area and materials, type of cooling (air, water, phase - obviously). For example, I would expect someone with a passive water kit to be much more affected by ambient temperature than someone with a radiator and 3 hulking fans on it.

I sort of wish there was a sub-ambient option that didn't come with many risks (condensation, failure), a huge price tag, and lots of noise. Then again, everyone would probably be doing it...

[aurareturn]

If it's 1:2, it's much more than I thought. I thought it might be 1:1. This explains why some people have much better cooling with the exact same setup.

This also explains that Anand does his HSF reviews in the North Pole.

[graysky]

Well, for my hardware it sure seems to be 1:2... your mileage may vary.

[Binky]

Very nice. Now if only I could keep my room that cold! Even your top end room temp of 23C is cooler than my room ever gets.

[graysky]

Where in the world are you located?

[graysky]

Updated 15-May with two higher temp points. It was like 85 °F outside today and I left the A/C off. Room got hot so I ran two additional points at about 76 and 77. Anyway, as you can see, it's all linear up to 77.5 °F and I suspect it'll continue that way if it gets hotter.

[graysky]

Updated 19-May: Fixed a small error and put formulas for both °F and °C (of your room temp) on the graph. The relationship is: for every °F change in room temp, the load TJunction changes by 1-1/2 °C. Well, this is true for my system, YMMV...

[graysky]

21-May Update: Re-ran the benchmark since it's been about 300 hours after the heatsink was seated on the AS5. You can see the temps have dropped by another 2-3 °C from when I initially seated it, so I guess the "break in" period is real.