# How big a generator to run A/C?



## Toller (Jan 2, 2013)

I am buying a standby generator. 
How big a generator do I need to run a 2.5ton Trane XL140?
I would be willing to shut everything off but the A/C for a few hours to cool the house off and then turn the A/C off.
I can live without A/C for a couple days so I doubt I will go for that, but would like to know my options.


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## kbsparky (Sep 11, 2008)

I have a 3-ton A/C unit and a 12 kW generator. The lights dim when that baby kicks on ...

While a 2.5 ton unit draws less, I'd stick with at least a 10 kW unit ....


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## stickboy1375 (Apr 28, 2012)

Toller said:


> I am buying a standby generator.
> How big a generator do I need to run a 2.5ton Trane XL140?
> I would be willing to shut everything off but the A/C for a few hours to cool the house off and then turn the A/C off.
> I can live without A/C for a couple days so I doubt I will go for that, but would like to know my options.



At least an 8 KW generator...and a hard start kit.

{edit}

I highly recommend the biggest unit you can afford.


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## Auger01 (Sep 13, 2011)

I run a 4 ton a.c. with a 10.8 kw 12kw surge generator. A 10KW unit should be able to run the average 2.5 ton a.c without too much trouble.


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## Billy_Bob (Sep 11, 2008)

Note that many HVAC units have electronic control boards these days (a computer basically) and these need "clean" electricity to operate. Many generators (especially the less expensive types) create "dirty" electricity and people have had trouble running their newer furnaces with these. Some generator manufacturers make "electronics friendly" generators, so best to get one of those.

Also another option would be to get a window air conditioner and just cool one room. Then you don't need such a large generator. But note many of these have electronic controls these days too! Actually EVERYTHING seems to have electronic controls now...


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## J. V. (Jun 1, 2007)

I have a 8kw with 11kw for extra hard starting generator and have never tried to run my 2.5 ton heat pump on it. We would need our generator in the winter, not the summer. I am thinking as long as I turn off the heat strips and just run the heat pump, it should be okay. I need to try and see. But I am not sure.
I am happy as long as I have hot water, fridge and freezer, a few lights and a computer and TV.


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## stickboy1375 (Apr 28, 2012)

J. V. said:


> I have a 8kw with 11kw for extra hard starting generator and have never tried to run my 2.5 ton heat pump on it. We would need our generator in the winter, not the summer. I am thinking as long as I turn off the heat strips and just run the heat pump, it should be okay. I need to try and see. But I am not sure.
> I am happy as long as I have hot water, fridge and freezer, a few lights and a computer and TV.


I couldn't start my 3 ton unit with a 7 KW generator...


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## Toller (Jan 2, 2013)

Billy_Bob said:


> Note that many HVAC units have electronic control boards these days (a computer basically) and these need "clean" electricity to operate. Many generators (especially the less expensive types) create "dirty" electricity and people have had trouble running their newer furnaces with these. Some generator manufacturers make "electronics friendly" generators, so best to get one of those.
> 
> Also another option would be to get a window air conditioner and just cool one room. Then you don't need such a large generator. But note many of these have electronic controls these days too! Actually EVERYTHING seems to have electronic controls now...


It claims to have less than 5% harmonic distortion, 1% voltage fluctuation, and constant 60hz. Lets hope.

I was thinking of just getting a portable A/C. We haven't been here in the summer, but had a cottage on the otherside of the lake and some years didn't use the window A/C. So maybe its not a big deal to do without.

Trane says I have to ask either my dealer or a generator vendor.
My dealer doesn't know.
Generac says to ask my installer.
My installer "thinks" a 10kw will be enough.

ARGH


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## stickboy1375 (Apr 28, 2012)

Toller said:


> Trane says I have to ask either my dealer or a generator vendor.
> My dealer doesn't know.
> Generac says to ask my installer.
> My installer "thinks" a 10kw will be enough.
> ...


The problem is every generator and compressor are different, so its no wonder people don't want to guarantee anything... Best bet is to really oversize a generator to ensure that you wont have any issues... or do without a monster of a load....


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## Auger01 (Sep 13, 2011)

http://www.five-two-one.com/

I have one of these installed. Generator doesnt bog down at all. They are about fifty bucks or less on amazon.


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## Kpack (Aug 4, 2012)

I believe the hard start on the ac with your gen is the way to go from what I've read that way you don't have  to get a big one there pretty tough on fuel I should listen to myself I have a 15k


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## stickboy1375 (Apr 28, 2012)

Kpack said:


> I believe the hard start on the ac with your gen is the way to go from what I've read that way you don't have  to get a big one there pretty tough on fuel I should listen to myself I have a 15k


Yeah, i MIGHT be able to start my 3 ton unit with a hard start kit, but to me, I have back up heat that is not electric, so its a moot point for me... AC is non essential to where I live either...


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## Toller (Jan 2, 2013)

A company selling the generator in question says the 8kw will run a 3ton A/C. I asked them where they got that information. They said it was supplied by Generac. They told me to look at the LRA on the plate; if it is under 50, the 8kw will start it.

Mine says 104! Presumably that means I need a 20kw generator to run it. That ain't happening.

So, is my LRA extremely high for a 2.5 ton A/C, or is Generac lying through their teeth when they say the 8kw will start a 3 ton A/C? Or is the company just confused?


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## Auger01 (Sep 13, 2011)

My four ton has a Lra less than 104. That seems way high for a 2.5 ton. A clamp meter would give you the actual start current.


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## md2lgyk (Jan 6, 2009)

There's certainly a lot of conflicting information when it comes to what size generator to power whatever. I live in a very rural area, and have power outages several times a year, often for a couple of days or more. Virtually all have been in the winter. Like stickboy, our backup heat is non-electric, and we also have a wood stove. So our biggest load would be the well pump. I don't know how many hp it is (though I know I'll have to find out before purchasing anything), but the well is 750 feet deep. Given the cost of some good generators, I suspect we'd be better off to just keep a few 5-gallon containers of water around, and use the 3kw genny I already have to power the fridge, freezer, and some lights and outlets.


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## J. V. (Jun 1, 2007)

stickboy1375 said:


> I couldn't start my 3 ton unit with a 7 KW generator...


"I don't know if my 8kw will start my 2.5 ton heat pump"???????????? 

I have never tried it. As a matter of fact, I have not needed the generator since I bought it.
I exercise it, so I will try to start the heat pump next time.


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## stickboy1375 (Apr 28, 2012)

J. V. said:


> "I don't know if my 8kw will start my 2.5 ton heat pump"????????????
> 
> I have never tried it. As a matter of fact, I have not needed the generator since I bought it.
> I exercise it, so I will try to start the heat pump next time.


I wasn't really expecting it too, i just tried it for ****s and giggles, because of the surge rating... but it failed.


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## frenchelectrican (Apr 12, 2006)

I don't know how much surge rating you have on the generatour unit and I know most portable units don't have much leeway before they stalled out.

In my house in Wisconsin I have 3 tonne A/C unit and with 5 KW slow speed diesel unit it barely make it so normally with large A/C unit I will just fired up the slow speed 20 KW unit that will take it without issue. ( both of my old units are able run in paraell mode ) 

Merci,
Marc


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## mikegp (Jul 17, 2011)

Billy_Bob said:


> Note that many HVAC units have electronic control boards these days (a computer basically) and these need "clean" electricity to operate. Many generators (especially the less expensive types) create "dirty" electricity and people have had trouble running their newer furnaces with these. Some generator manufacturers make "electronics friendly" generators, so best to get one of those.
> 
> Also another option would be to get a window air conditioner and just cool one room. Then you don't need such a large generator. But note many of these have electronic controls these days too! Actually EVERYTHING seems to have electronic controls now...


How do you know what generators to use?


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## herdfan (Jul 7, 2012)

Toller said:


> A company selling the generator in question says the 8kw will run a 3ton A/C. I asked them where they got that information. They said it was supplied by Generac.


Generac's advertising says my 17Kw will start a 5-ton A/C. Mine will not. When I was installing it, I tested with just the A/C and air handler and it would not start it.

Runs a 3-ton unit just fine with all other loads on as well.


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