# Help Choosing A/C Size



## jasonsservices (Jan 23, 2012)

I recently added a room on to the house I am living in. It's time to put in an 110 A/C window unit. I need to get the largest size possible (I need to cool a connecting room also). I have a dedicated line with 12 gauge wire and a 20 amp breaker. The outlet has not been added yet. What are my limitations?

Thanks for the help!

Jason


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## 480sparky (Feb 1, 2009)

You're limited to a 20amp circuit. Whether that's enough power to cool the room......... that's a tin-knocker question.


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## Inner10 (Mar 12, 2009)

Why a window shaker?


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## jasonsservices (Jan 23, 2012)

Thanks for the answer Sparky. 

What do those 110 units with the odd shaped plugs require. Are those 30 amp? If so, I guess I would have to run heavier gauge wire to upgrade to 30 amp service (and of course a 30 amp breaker).



Inner10 said:


> Why a window shaker?


The window unit is our only real option. This is a old, small house that I rent. We love where it is located (in a country setting) and the rent is low. However, it just got to be too small. The choice was either move, or add on at our expense. We chose to add on (we used the enclosed carport as the starting point, so the expense wasn't all that much). The house has nothing central, all heat and air is window and wall units. So this is our only real option in the new room. I would like to have allowed for a 220 set up, but the existing box is so small, I only could only dedicate one circuit to the ac.


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## 480sparky (Feb 1, 2009)

If the outlet is 











or










then you can plug in any standard 120v household unit.


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## TxElectrician (May 21, 2008)

Fixed it for you



480sparky said:


> If the outlet is
> 
> 
> 
> ...


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## 480sparky (Feb 1, 2009)

TxElectrician said:


> Fixed it for you


Provide a code reference, please. :laughing:


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## rselectric1 (Sep 20, 2009)

480sparky said:


> Provide a code reference, please. :laughing:


:laughing::laughing::laughing:

Watch those falling metal coverplates!!!!!!!


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## SemiRetiredEL (Nov 24, 2009)

jasonsservices said:


> I recently added a room on to the house I am living in. It's time to put in an 110 A/C window unit. I need to get the largest size possible (I need to cool a connecting room also). I have a dedicated line with 12 gauge wire and a 20 amp breaker. The outlet has not been added yet. What are my limitations?
> 
> Thanks for the help!
> 
> Jason


If the line is dedicated #12 simply install a 1/2 space 240V breaker (if possible) and 240V receptacle for the window unit.

240V units save energy and will provide twice the cooling. 

Also have you considered a portable heat & cool unit? They provide up to 13,000 BTU/hr and only draw 10A @ 120V.


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## Inner10 (Mar 12, 2009)

SemiRetiredEL said:


> If the line is dedicated #12 simply install a 1/2 space 240V breaker (if possible) and 240V receptacle for the window unit.
> 
> 240V units save energy and will provide twice the cooling.
> 
> Also have you considered a portable heat & cool unit? They provide up to 13,000 BTU/hr and only draw 10A @ 120V.


A 240V motor may be a hair more efficient and have greater starting power but I wouldn't say they really save energy.

How efficient are portable units? I always figured they would be pretty lousy since they have to pipe hot air out...and what about the condensate? Do you have to empty a bucket every few hours?

The problem I have with window shakers is they leave a big gaping hole between your house and the world outside, noisy and ugly. If you are planning on staying there a while I'd put a split system in.


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## Tinstaafl (Jan 6, 2008)

Inner10 said:


> A 240V motor may be a hair more efficient and have greater starting power but I wouldn't say they really save energy.


There's a reason POCOs use high voltage to carry their product over long distances. Of course it saves energy. :thumbsup:


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## Inner10 (Mar 12, 2009)

Tinstaafl said:


> There's a reason POCOs use high voltage to carry their product over long distances. Of course it saves energy. :thumbsup:


Because of the cost of wire...or it is a conspiracy with the companies the build transformers?


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## Tinstaafl (Jan 6, 2008)

Because the resistance of the wire causes a voltage drop, resulting in less power available at the destination.


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## 480sparky (Feb 1, 2009)

SemiRetiredEL said:


> .........240V units save energy and will provide twice the cooling. .........



Since when? If this is true, then ALL our stuff would be 240v.


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## Inner10 (Mar 12, 2009)

Tinstaafl said:


> Because the resistance of the wire causes a voltage drop, resulting in less power available at the destination.


In that case the OP should run a HVDC power to the window shaker to minimize his electrical losses.:laughing:


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## SemiRetiredEL (Nov 24, 2009)

Inner10 said:


> A 240V motor may be a hair more efficient and have greater starting power but I wouldn't say they really save energy.
> 
> How efficient are portable units? I always figured they would be pretty lousy since they have to pipe hot air out...and what about the condensate? Do you have to empty a bucket every few hours?
> 
> The problem I have with window shakers is they leave a big gaping hole between your house and the world outside, noisy and ugly. If you are planning on staying there a while I'd put a split system in.


The higher voltage allows twice the power thru the same wire, the wire stays cooler so the I^2 r losses (copper losses)are smaller.

No SEER numbers are available for the "portable heat pump units" but they are said to be able cool or heat a 400 sq ft room. I have one in my van and love it. Mine has a gravity drain for condensate, others exhaust the condensate with the exhaust.


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## SemiRetiredEL (Nov 24, 2009)

480sparky said:


> Since when? If this is true, then ALL our stuff would be 240v.


Copper losses are a function of current (I^2R). The higher the voltage the lower the current for the same wattage.

That's why power companies use high voltage transmission lines, not 120V. Same for Europe.


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## 480sparky (Feb 1, 2009)

SemiRetiredEL said:


> Copper losses are a function of current (I^2R). The higher the voltage the lower the current for the same wattage.
> 
> That's why power companies use high voltage transmission lines, not 120V. Same for Europe.


But going from 120 to 240 volts is NOT going to double your efficiency or cut your power bill in half!


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## Tinstaafl (Jan 6, 2008)

480sparky said:


> But going from 120 to 240 volts is NOT going to double your efficiency or cut your power bill in half!


No it's not. Do you deny that there is any theoretical difference in efficiency at all?


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## 480sparky (Feb 1, 2009)

Tinstaafl said:


> No it's not. Do you deny that there is any theoretical difference in efficiency at all?


I never said that. I'm simply saying using a 240v unit is not going to run at half the cost of a 120v one.


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## SemiRetiredEL (Nov 24, 2009)

480sparky said:


> I never said that. I'm simply saying using a 240v unit is not going to run at half the cost of a 120v one.



"240V units save energy and will provide twice the cooling."

It will save a very small amount of energy and allow twice as much energy (which will have to be paid for by the user) to flow to the A/C unit, without changing wire size.:clap:

I never said it would save 50% of the energy cost.:no:


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## 480sparky (Feb 1, 2009)

SemiRetiredEL said:


> "240V units save energy and will provide twice the cooling."
> 
> It will save a very small amount of energy and allow twice as much energy (which will have to be paid for by the user) to flow to the A/C unit, without changing wire size.:clap:
> 
> I never said it would save 50% of the energy cost.:no:


So "No extra costs plus you get twice as much cooling" doesn't mean, "Same amount of money, half the cost"?


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## SemiRetiredEL (Nov 24, 2009)

jasonsservices said:


> I recently added a room on to the house I am living in. It's time to put in an 110 A/C window unit. I need to get the largest size possible (I need to cool a connecting room also). I have a dedicated line with 12 gauge wire and a 20 amp breaker. The outlet has not been added yet. What are my limitations?
> 
> Thanks for the help!
> 
> Jason


If you need more cooling in an area than a dedicated 120V 20A circuit can provide, you have the option of changing that circuit to 240V 20A without running new wire.

This will allow you to install an AC with twice the cooling capacity as a 120V unit and even achieve some small savings in electrical usage.


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## jasonsservices (Jan 23, 2012)

SemiRetiredEL said:


> If you need more cooling in an area than a dedicated 120V 20A circuit can provide, you have the option of changing that circuit to 240V 20A without running new wire.
> 
> This will allow you to install an AC with twice the cooling capacity as a 120V unit and even achieve some small savings in electrical usage.


To switch to a 240v, wouldn't I need two spaces available in my breaker box? If the answer is yes, then the option is out. I think I failed to mention that my breaker box has no space left. It was pushing it just to get the dedicated 20amp line. 

Thanks everyone for the input! It looks like I will just get the largest btu I can get with my 20amp set up and hope Oklahoma doesn't have a repeat of last summer.


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## Tinstaafl (Jan 6, 2008)

jasonsservices said:


> To switch to a 240v, wouldn't I need two spaces available in my breaker box?


Yes. But if all your breakers are standard size, you could substitute a couple of mini-breakers, which fit two into the space of one. You just have to make sure that your double breaker is tapping off both busses.


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## 480sparky (Feb 1, 2009)

Tinstaafl said:


> Yes. But if all your breakers are standard size, you could substitute a couple of mini-breakers, which fit two into the space of one. You just have to make sure that your double breaker is tapping off both busses.


*IF* your panel is rated for them.


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## jasonsservices (Jan 23, 2012)

Tinstaafl said:


> Yes. But if all your breakers are standard size, you could substitute a couple of mini-breakers, which fit two into the space of one. You just have to make sure that your double breaker is tapping off both busses.


I can't figure how putting two mini's into the slot of one standard could tap off of both busses (I am assuming that "busses" are the two main bars running down the breaker box). But then again, I am not electrician. Though I doubt it's the route I am going to go, I am curious as to how it could work. I guess it's time to give Google some business and see what I can learn.


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## Tinstaafl (Jan 6, 2008)

Sorry Jason, but if you don't follow, probably the best idea is to call in an electrician. :thumbsup:


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## jasonsservices (Jan 23, 2012)

Tinstaafl said:


> Sorry Jason, but if you don't follow, probably the best idea is to call in an electrician. :thumbsup:


Are you kidding? If a real electrician looked at my box, he'd just shake his head and run. 

Ok, well it's probably not that bad, but, I am sure it has a few code violations. I've cleaned it up since I have lived in this house, so it's at least better than what it was, but it still has a few questionable items.

Regarding following what your talking about, I'm sure that a good picture or a peek behind my panel would clear things up, but sitting where I am at now without a picture to look at, I can't grasp how two minis in one slot can touch both bars. I though that is why you had to use two slots for 220. Each breaker makes contact with it's own 110, giving you 220. When it's priority, I will research it and then understand it, but for now I will just have to remain ignorant.


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## Tinstaafl (Jan 6, 2008)

jasonsservices said:


> I can't grasp how two minis in one slot can touch both bars.


I really shouldn't go there, but what the heck. Two minis will leave a full slot open. Two more will leave another full slot open. Two full slots will give you the two-buss connection you need.


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## 480sparky (Feb 1, 2009)

There _are_ panel brands where two minis/thin/piggyback/tandem breakers will hook onto two bus bars giving you 240.






























Just remember, the panel must be a certain brand, and be listed for accepting them.



See how _easy_ electrical is? :jester:


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## Tinstaafl (Jan 6, 2008)

Of course it's easy, as long as you can provoke Ken into a helpful answer. :jester:


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## 480sparky (Feb 1, 2009)

Were I to provide a truly 'helpful' answer, I would be dismissed as being too technical and long-winded. This would be interpreted as me being an azzhole, which results in my 'helpful' answer being ignored. The outcome of which will be the person doing whatever it takes to get the job done cheaply, ultimately ending in an unsafe installation simply because a 'correct' one is just 'too much money/hassle' or is 'too complicated'.


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## Tinstaafl (Jan 6, 2008)

I know Ken, we've talked about this before. I don't dispute that does happen on occasion, but there's no way to know how many lurkers will or won't actually heed good advice. It's all too easy to base your feelings about that on the few squeaky wheels that give you a hard time about it.

Most folks want to do it right. :thumbsup:


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## jasonsservices (Jan 23, 2012)

Good ol' pictures! I understand. So in reality, it takes four minis to make this work?

As I mentioned before, I don't think this is the route I am going to take (my box probably wouldn't accommodate it any way), but I do appreciate you clearing this up for me.

Thanks!


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## 480sparky (Feb 1, 2009)

Tinstaafl said:


> .........Most folks want to do it right. :thumbsup:


Who's up for a Load Calculation? :whistling


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## Tinstaafl (Jan 6, 2008)

480sparky said:


> Who's up for a Load Calculation? :whistling


I'd be up for a tutorial. I freely admit I've never had occasion to do one.


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## 480sparky (Feb 1, 2009)

Tinstaafl said:


> I'd be up for a tutorial. I freely admit I've never had occasion to do one.


We'll need the real, hard data from the OP.


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## woodchuck2 (Feb 27, 2008)

Tinstaafl said:


> I'd be up for a tutorial. I freely admit I've never had occasion to do one.


Ahhh, it so easy a 12 yr old can do it :whistling


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## Tinstaafl (Jan 6, 2008)

woodchuck2 said:


> Ahhh, it so easy a 12 yr old can do it :whistling


Most of this stuff is. If the 12 year old has been taught how. :thumbsup:


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