# Thermodynamics question **URL:** \ **Category:** Factual Questions\ **Created:** [December 17, 2003, 11:50pm UTC](https://boards.straightdope.com/t/thermodynamics-question/219653 "2003-12-17T23:50:14Z")\ **Posts on this page:** 5\ **Page:** 3
**Author:** ![Hyperelastic](https://avatars.discourse-cdn.com/v4/letter/h/a3d4f5/32.png) [@Hyperelastic](https://boards.straightdope.com/u/Hyperelastic)\ **Post date:** [December 20, 2003, 2:38am UTC](https://boards.straightdope.com/t/thermodynamics-question/219653/41 "2003-12-20T02:38:53Z")
> [@](#): > > \*Originally posted by David Simmons \* > \*\*Of course the refrigerator doesn’t run all of the time, does it? When it stops the kinetic energy is turned into heat by the friction in the machine. And then it delivers its heat to the lower temperature environment. Over the long haul, all of the energy delivered to the refigerator comes out as heat except the kinetic energy existing at the moment and that is but an insignificant fraction of the total energy delivered to the machine over a period of time. \*\* What you say is correct, except that the part about the kinetic energy being insignificant depends on what you call insignificant. Also, you correctly note that to get all the energy used by the refrigerator into heating the room air, you have to turn the refrigerator off and wait until everything equilibrates, i.e. an infinite time. Several posters have run a long way with the fact that all energy ends up as heat eventually, but do not quite appreciate the additional facts that one must wait infinitely long for that to happen and that the amount of heat that goes into “heating the room” can differ between the heater and other appliances like light bulbs. Whether these additional facts are considered relevant to the OP, or quibbles, I suppose we all have to decide for ourselves. Consider two rooms, equal in every way, except that Room A is heated by a 1500 W heater, while Room B has a 1500 W spotlight shining directly out the window. Which room do you think is going to be warmer? ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [December 20, 2003, 3:25am UTC](https://boards.straightdope.com/t/thermodynamics-question/219653/42 "2003-12-20T03:25:52Z")
In practical terms, allowing a refrigerator’s compressor to cool down to ambient takes only a few hours. So in this case infinity = 8h or less. Also, the compressor on a refrigerator must sooner or later achieve a steady state rate of heat transfer to the room. Until it does so, it will continue to heat up. At the steady state, the amount of electrical energy going into the fridge is _exactly equal_ to the amount coming out as heat. ---
**Author:** ![sailor](https://avatars.discourse-cdn.com/v4/letter/s/a587f6/32.png) [@sailor](https://boards.straightdope.com/u/sailor)\ **Post date:** [December 20, 2003, 3:43am UTC](https://boards.straightdope.com/t/thermodynamics-question/219653/43 "2003-12-20T03:43:23Z")
> [@](#): > > \*Originally posted by Hyperelastic \* > Several posters have run a long way with the fact that all energy ends up as heat eventually, but do not quite appreciate the additional facts that one must wait infinitely long for that to happen and that the amount of heat that goes into “heating the room” can differ between the heater and other appliances like light bulbs. Whether these additional facts are considered relevant to the OP, or quibbles, I suppose we all have to decide for ourselves. 100% quibbles. Infinitely long time is wrong for two reasons: (a) the time constant for the compressor heat loss is minutes, not hours. In less than an hour after it stops the compressor will be at room temperature for all practical purposes. In any case, it does not matter. The only heat invested and stored is the equivalent of warming the compressor _once_ which is a ridiculously low amount. Any further injection of heat is heat which has already been transferred to the room. In other words, for all practical purposes, it does not matter where the energy went, it all ends up as heat. > [@](#): > > Consider two rooms, equal in every way, except that Room A is heated by a 1500 W heater, while Room B has a 1500 W spotlight shining directly out the window. Which room do you think is going to be warmer? What does that have to do with anything? An infrared heater would transfer energy out the window too. In that sense the heat from the refrigerator is better than any heater. Let us not make silly scenarios. The Op is quite clear in what it asks, let us not twist it. ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [December 20, 2003, 3:53am UTC](https://boards.straightdope.com/t/thermodynamics-question/219653/44 "2003-12-20T03:53:09Z")
> [@](#): > > \*Originally posted by sailor \* > Let us not make silly scenarios. Does that mean we can’t consider the case where the refrigerator is blocking the window, or worse, halfway out the window? 😉 ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [December 20, 2003, 4:44am UTC](https://boards.straightdope.com/t/thermodynamics-question/219653/45 "2003-12-20T04:44:44Z")
> [@](#): > > \*Originally posted by Hyperelastic > > > [@](#): > > > > Originally posted by David Simmons \*\*\* > > Of course the refrigerator doesn’t run all of the time, does it? When it stops the kinetic energy is turned into heat by the friction in the machine. And then it delivers its heat to the lower temperature environment. Over the long haul, all of the energy delivered to the refigerator comes out as heat except the kinetic energy existing at the moment and that is but an insignificant fraction of the total energy delivered to the machine over a period of time. > > What you say is correct, except that the part about the kinetic energy being insignificant depends on what you call insignificant. Also, you correctly note that to get all the energy used by the refrigerator into heating the room air, you have to turn the refrigerator off and wait until everything equilibrates, i.e. an infinite time. > \*\* **Squink** and **sailor** have adequately answered your objection. I can’t add anything useful to what they wrote. > [@](#): > > \*\* > Consider two rooms, equal in every way, except that Room A is heated by a 1500 W heater, while Room B has a 1500 W spotlight shining directly out the window. Which room do you think is going to be warmer?\*\* Nothing like a stacked deck. If you have the light shining out the window in Room B, then I want all of the output from your heater ducted out the window in Room A. [Previous page](https://boards.straightdope.com/t/thermodynamics-question/219653.md?page=2)