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Effect of room temp on your CPU load temps

Last response: in Overclocking
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May 13, 2007 3:51:01 PM

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:
[code:1:2451979b48]Core temp = TJunction - DTS

Example, DTS reads 62. You take 100-62=38 and your core temp is 38 °C.[/code:1:2451979b48]
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 15 °C to each temp (the table is CORRECTED temps). 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).



Raw data table in case you want the individual points:



Downloads and References
To download crystalCPUID: http://crystalmark.info/software/CrystalCPUID/index-e.html
To download rmclock: http://cpu.rightmark.org/products/rmclock.shtml
To download speedfan: http://www.almico.com/speedfan.php
To download TAT: http://www.techpowerup.com/downloads/392/mirrors.php

To read more about TJunction and for a discussion about other things relating to thermal output fromC2D chips, see: http://forumz.tomshardware.com/hardware/modules.php?name=Forums&file=viewtopic&t=221745
May 16, 2007 1:14:49 AM

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.
May 19, 2007 8:11:26 PM

Yeah, common sense, but now I have data to back-it-up :) 

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...
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August 4, 2007 4:01:24 PM

Nice work!

I'll have to leave the window open this winter when I'm gaming with my Quad. I have a feeling that I'll get plenty of heat from my computer case ;)  I live in the North country.
August 5, 2007 2:39:59 AM

gooman said:
Nice work!

I'll have to leave the window open this winter when I'm gaming with my Quad. I have a feeling that I'll get plenty of heat from my computer case ;)  I live in the North country.


eh, i live in the south east of the us and i have the ac on. the house is 20-21c and my room is a const of 26c-29c. with air conditioning off... well my room burns up. sometimes i have to leave my door open because if i don't i think i might have a heatstroke.


computer stays around 45C ( mobo and other stuff) cpu goes to the high 60c. ( with ocing its at 70c and the mobo is 53c)

i have been having my room around that temperature for a good while and now i am pretty much use to it. mom and dad stepped into my room one day and left out of the house and bought me 2 cacti and a banana plant.


stupid p180b. i never hear my computer but i feel the heat.
!