# Cooling a room with Peltiers **URL:** \ **Category:** Factual Questions\ **Created:** [June 10, 2014, 12:51am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448 "2014-06-10T00:51:32Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![boffking](https://avatars.discourse-cdn.com/v4/letter/b/858c86/32.png) [@boffking](https://boards.straightdope.com/u/boffking)\ **Post date:** [June 10, 2014, 12:51am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/1 "2014-06-10T00:51:32Z")
I have an 8x12 bedroom that gets way too hot in the summer. I can’t fit an AC in the window and I don’t have enough space for a portable one. How many Peltier coolers would it take to make my room comfortable and how much would it cost? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [June 10, 2014, 1:35am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/2 "2014-06-10T01:35:25Z")
They’re terribly inefficient. And very expensive. It would be tens of thousands of dollars in modules, and probably hundreds of dollars in electricity every month. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [June 10, 2014, 2:49am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/3 "2014-06-10T02:49:41Z")
They make them for big cabinets full of electrical equipment: [http://go.eicsolutions.com/peltier-thermoelectric-coolers-b?utm\_source=google&utm\_medium=ppc&utm\_content=Peltier%20Cooling&utm\_campaign=Thermoelectric%20Air%20Conditioners&pi\_ad\_id=34682137382&gclid=CNmOyrSl7r4CFahAMgodty8AqA](http://go.eicsolutions.com/peltier-thermoelectric-coolers-b?utm_source=google&utm_medium=ppc&utm_content=Peltier%20Cooling&utm_campaign=Thermoelectric%20Air%20Conditioners&pi_ad_id=34682137382&gclid=CNmOyrSl7r4CFahAMgodty8AqA) I think they’d be expensive to buy and run, and not competitive with mechanical AC, but maybe practical unto themselves. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [June 10, 2014, 4:36am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/4 "2014-06-10T04:36:57Z")
As **beowulff** said, they aren’t very efficient, and they are a bit on the pricey side. Peltiers work like itty bitty heat pumps. You run electric current through them, and they move heat from one side to the other. They also generate their own heat in the process, so you have to be good about removing heat from the hot side or they’ll just go into thermal runaway and overheat. If you are just thinking that you can stick them in a room and they’ll make the room cooler, they don’t work like that. Peltiers are neat little devices. Reverse the current and the hot side becomes the cool side and the cool side becomes the hot side. They also work as generators. Apply a heat differential to each side and they will generate electricity (again, they aren’t very efficient). They are neat little devices and they work well for cooling PC CPUs and picnic style coolers. They aren’t your best choice for cooling a room though. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [June 10, 2014, 4:49am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/5 "2014-06-10T04:49:42Z")
By the way, rough back of the envelope calculation, you’ll need probably somewhere around 4,000 BTU to cool a room of that size. Figuring maybe 50 BTU per peltier, you’d need around 80 of them. At about 5 bucks apiece, that’s $400 just for the peltiers, not including heat sinks, mounting hardware, and fans to draw the heat off of the hot side. For comparison, you can buy a 5,000 BTU air conditioner for $140 or so. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [June 10, 2014, 4:57am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/6 "2014-06-10T04:57:46Z")
and you would need to isolate the hot side and the heat extracted from it from the cold box you would need to made in the room. it would be a monetary, technological and energy disaster. ---
**Author:** ![Magiver](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@Magiver](https://boards.straightdope.com/u/Magiver)\ **Post date:** [June 10, 2014, 5:00am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/7 "2014-06-10T05:00:25Z")
> [@boffking](#): > > I have an 8x12 bedroom that gets way too hot in the summer. I can’t fit an AC in the window and I don’t have enough space for a portable one. How many Peltier coolers would it take to make my room comfortable and how much would it cost? free standing units don’t take up that much space. You can either suffer in the heat or give up the floor space of a waste paper basket. For that matter you could build a shelf next to a window and get it up off the floor. You’ll have to cobble together a panel in the window for the exhaust hose. ---
**Author:** ![bob\_2](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bob_2/32/3341_2.png) [@bob\_2](https://boards.straightdope.com/u/bob_2)\ **Post date:** [June 10, 2014, 9:42am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/8 "2014-06-10T09:42:15Z")
This reminds me of the old 4th grade question that goes something like: If your 5 cubic foot fridge can get down to 40F in 1 hour, how long would it take to cool your 1000 cubic foot kitchen if you left the door open? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [June 10, 2014, 10:54am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/9 "2014-06-10T10:54:46Z")
> [@johnpost](#): > > and you would need to isolate the hot side and the heat extracted from it from the cold box you would need to made in the room. > > it would be a monetary, technological and energy disaster. And most likely bigger than a portable AC unit. ---
**Author:** ![busterpickle](https://avatars.discourse-cdn.com/v4/letter/b/258eb7/32.png) [@busterpickle](https://boards.straightdope.com/u/busterpickle)\ **Post date:** [June 10, 2014, 5:58pm UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/10 "2014-06-10T17:58:38Z")
You can always put a portable A/C unit on a shelf and run the hoses down/around to the window for the heat exhaust. I have no idea if an A/C unit can be rotated 90 degrees and still work properly (compressor issues maybe?) but that might allow for more space. ---
**Author:** ![Magiver](https://avatars.discourse-cdn.com/v4/letter/m/4491bb/32.png) [@Magiver](https://boards.straightdope.com/u/Magiver)\ **Post date:** [June 10, 2014, 6:42pm UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/11 "2014-06-10T18:42:37Z")
If this is a problem because of a thin vertical window then all it requires for a portable air conditioner is to make a spacer with a port for the exhaust hose. You can use clear plastic panels or glass. The price of plastic has gone up considerably so it might be cheaper to make a simple wood frame to fit the open window and glaze in glass panes. screw the panel in place and seal it with silicone if necessary. About $15 if you make it yourself. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [June 11, 2014, 4:13am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/12 "2014-06-11T04:13:42Z")
Maybe my setup was inefficient, but heat sinks hardly did anything for my TE device. It would cool maybe 20°C, then the heat generated got so great that both sides ended up being hotter than room temperature. I had to put dry ice around the heat sink. I’m thinking, normal compression cooling uses radiators to dissipate heat, which are more powerful than heat sinks. TE cooling, which is less efficient, thus producing more waste heat, will require even more powerful dissipation, maybe water cooling with a reservoir. So, if you’re still thinking about this, budget for more than a chunk of aluminium and a fan. ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [June 11, 2014, 6:41am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/13 "2014-06-11T06:41:48Z")
> [@AaronX](#): > > Maybe my setup was inefficient, but heat sinks hardly did anything for my TE device. It would cool maybe 20°C, then the heat generated got so great that both sides ended up being hotter than room temperature. I had to put dry ice around the heat sink. Did you have a fan on the heat sink? How big was the heat sink? If you’re pumping a lot of heat, then yeah, getting rid of the waste heat does become an issue. It typically ends up being a lot more heat than a small passive heat sink can handle. Fans help. I’ve also used water cooling in some applications. ---
**Author:** ![AaronX](https://avatars.discourse-cdn.com/v4/letter/a/7bcc69/32.png) [@AaronX](https://boards.straightdope.com/u/AaronX)\ **Post date:** [June 12, 2014, 8:28am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/14 "2014-06-12T08:28:44Z")
No fan. About 10x4x5 cm. ---
**Author:** ![Isilder](https://avatars.discourse-cdn.com/v4/letter/i/cc9497/32.png) [@Isilder](https://boards.straightdope.com/u/Isilder)\ **Post date:** [June 12, 2014, 8:57am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/15 "2014-06-12T08:57:46Z")
[quote=“AaronX, post:12, topic:690448”] Maybe my setup was inefficient, but heat sinks hardly did anything for my TE device. It would cool maybe 20°C, then the heat generated got so great that both sides ended up being hotter than room temperature. I had to put dry ice around the heat sink. I’m thinking, normal compression cooling uses radiators to dissipate heat, which are more powerful than heat sinks. /QUOTE] The computer industry use of the word “heat sink” is a misnomer. A heat sink is device to smooth out the highs with the lows…eg night and day. The point is that there must be an on (heat up ) and off time (cools down) ! So these devices you are thinking of _are_ radiators … radiator" is also misnomer because the dominant effect is heat conductance into the air… with air flow perhaps due to convection… They have a larger surface area so that the rooms draft cools them… If you don’t have forces air cooling blowing the heat outside your computer case, the largest heat sink or cpu inside won’t help ! And that brings me back to the OP… I did’t get how he was going to move the heat outside of the room. Peltier junctions don’t make “cold” from electricity… there is no such thing as cold - they are a heat pump that moves the heat… somewhere. ---
**Author:** ![Darth\_Panda](https://avatars.discourse-cdn.com/v4/letter/d/ee7513/32.png) [@Darth\_Panda](https://boards.straightdope.com/u/Darth_Panda)\ **Post date:** [June 12, 2014, 10:29am UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/16 "2014-06-12T10:29:34Z")
> [@Isilder](#): > > And that brings me back to the OP… I did’t get how he was going to move the heat outside of the room. Peltier junctions don’t make “cold” from electricity… there is no such thing as cold - they are a heat pump that moves the heat… somewhere. Yeah, the net effect won’t be much different than trying to cool the room by leaving the refrigerator door open. If you can’t do AC for whatever reason, get a bucket of ice and a fan. ---
**Author:** ![johnpost](https://avatars.discourse-cdn.com/v4/letter/j/f17d59/32.png) [@johnpost](https://boards.straightdope.com/u/johnpost)\ **Post date:** [June 12, 2014, 3:04pm UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/17 "2014-06-12T15:04:45Z")
fans with ducting are much better from removing heat from heat sinks than just fans alone. ---
**Author:** ![busterpickle](https://avatars.discourse-cdn.com/v4/letter/b/258eb7/32.png) [@busterpickle](https://boards.straightdope.com/u/busterpickle)\ **Post date:** [June 12, 2014, 3:58pm UTC](https://boards.straightdope.com/t/cooling-a-room-with-peltiers/690448/18 "2014-06-12T15:58:21Z")
> [@engineer\_comp\_geek](#): > > By the way, rough back of the envelope calculation, you’ll need probably somewhere around 4,000 BTU to cool a room of that size. Figuring maybe 50 BTU per peltier, you’d need around 80 of them. > > At about 5 bucks apiece, that’s $400 just for the peltiers, not including heat sinks, mounting hardware, and fans to draw the heat off of the hot side. > > For comparison, you can buy a 5,000 BTU air conditioner for $140 or so. And, that, is a “gross” figure. Once you factor in real-world losses, one would probabaly discount that by… say… 30%, to be safe, and have a bit of a margin? > [@AaronX](#): > > Maybe my setup was inefficient, but heat sinks hardly did anything for my TE device. It would cool maybe 20°C, then the heat generated got so great that both sides ended up being hotter than room temperature. I had to put dry ice around the heat sink. Your heatsink (or whatever) has to be able to dissipate the heat from the CPU as well as the TE. Factor in any ineffeciencies and the air temp within the computer case, and, you’ll need a much larger heatsink then you think. So, a 12V@5A TE is 60 watts, throw in your CPU, which could be 70-120 watts (I’m assuming a high performace CPU), +30% (I use 30% a lot, higher internal case temp versus outside the case, etc), and you’re gonna need a heatsink that is designed for 240 watts. That’s a pretty big heatsink believe it or not, even if it is fan cooled. “Back in the day”, late 90’s early 00’s, I would design as above but for a heatsink not using a fan. Then, add a fan. I had some very complex ducting setups back then.