# Thermostat Puzzle

**URL:** http://discourse.iapct.org/t/thermostat-puzzle/11582
**Category:** CSG1995
**Created:** [November 30, 1995, 11:02am UTC](http://discourse.iapct.org/t/thermostat-puzzle/11582 "1995-11-30T11:02:39Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![Fred\_Nickols](http://discourse.iapct.org/letter_avatar_proxy/v4/letter/f/d9b06d/32.png) [@Fred\_Nickols](http://discourse.iapct.org/u/Fred_Nickols)
#### Post date: [November 30, 1995, 11:02am UTC](http://discourse.iapct.org/t/thermostat-puzzle/11582/1 "1995-11-30T11:02:39Z")

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Fred Nickols [951130.0550 EST]

Bill Powers recently posed a thermostat puzzle.

&nbsp;&nbsp;&nbsp;&nbsp;[From Bill Powers (951128.0805 MST)]

&nbsp;&nbsp;&nbsp;&nbsp;A rather neat example of spurious cause and effect showed up this  
&nbsp;&nbsp;&nbsp;&nbsp;morning. The living room was pretty chilly when we got up, so we turned  
&nbsp;&nbsp;&nbsp;&nbsp;on the solar heating register by turning up the thermostat to the  
&nbsp;&nbsp;&nbsp;&nbsp;daytime setting. This was half an hour before dawn. Then a nice clear  
&nbsp;&nbsp;&nbsp;&nbsp;day dawned, the sun came up, and Mary opened the curtains to let the  
&nbsp;&nbsp;&nbsp;&nbsp;sunshine in through windows and the patio door (all Thermopane) and warm  
&nbsp;&nbsp;&nbsp;&nbsp;up the room faster. Half an hour after that, the living room was cold  
&nbsp;&nbsp;&nbsp;&nbsp;again. So we found empirically that letting the sun shine into the room  
&nbsp;&nbsp;&nbsp;&nbsp;caused the room to get colder! Can you guess what mechanism was  
&nbsp;&nbsp;&nbsp;&nbsp;responsible for this negative effect of heat input on temperature?

My guess is that the direct rays of the sunlight  
fell on the thermostat. This altered the thermostat's  
perception of the room temperature, making it think  
the room was warmer than it really was. Its design is  
such that it does not control for room temperature but  
only for temperature in its immediate vicinity. In any  
case, the thermostat is responsible for maintaining the  
appropriate room temperature and it didn't. For such  
sloppy work the thermostat should receive a damning  
performance appraisal, placed on disciplinary warning  
and, if its performance does not improve, it should be  
terminated. The only mitigating factor that comes to  
mind is that the thermostat might be like my daughter,  
really groggy in the morning hours--grumpy, too.