# What Size Generator To Run 5 Ton AC Unit? (Calculated)

5 ton AC unit is one of the biggest that can be powered by a generator.

A 5 ton AC unit generates an outstanding 60,000 BTU of cooling power. This is enough to cool down up to 3000 square feet home.

How many watts does it take to run such a 5-ton air conditioner?

5 ton AC wattage can be anywhere between 4,000W to 8,000W. That’s between 16 and 34 Amps (240V circuit).

It gets tricky when we try to determine the size of a generator that can run a 5 ton AC unit.

The key thing is to figure out the overall wattage of such a big central air conditioner. Here are 3 simple ways you can do that:

1. Check the specification sheet for Power (measured in Watts).
2. Check the specification sheet for the EER rating. We can calculate wattage by dividing BTUs with EER rating; i.e. 60,000 BTU / 10 EER = 6,000W.
3. Check the specification sheet for the current (I, measured in Amps) and voltage (V, measured in Volts). We can calculate wattage by multiplying current with voltage; i.e., 25 Amps * 240V = 6,000W.

An average 5-ton air conditioner (with 10 EER rating) will run on 6,000 W.

Such a 5-ton air conditioner will use 25 Amps at 240V.

Examples of 60,000 BTU units are 4-zone mini-splits and 5-zone mini-split air conditioners.

## 6,000 W Generator For 5 Ton AC Unit

For most 5-ton air conditioners, 6,000 W power generators will be more than enough. Of course, we also need to think about the start-up wattage. Because these AC units need a lot of power, the safe choice is to get a generator that can handle at least 7,000 W start-up wattage.

The best – and most popular – 5-ton AC unit generator is the Westinghouse WGen6000. It’s a 6,000W generator that can deliver up to 7,500W of power; perfect for a 5-ton air conditioner.

This will be more than enough to run a powerful air conditioner optimally.

### 51 thoughts on “What Size Generator To Run 5 Ton AC Unit? (Calculated)”

1. So, for start up calculations you wouldn’t use the LRA rating for the amperage value of a condenser unit? Using the above method, a 48kV generator would be sufficient for six (5-ton) units?

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• Hello Miles, you’re correct; LRA rating is not used for a start up calculation. 48kW generator will run 6 units if they don’t surpass 8000W per unit (usually 5-ton units need about 6000W of power).

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• LRA locked rotor ampere – only if something wrong with compressor.
USE RLA (rated load amps) rating NOT LRA. Yes starting current will be high
so need to free some power using smart management module or have higher capacity generator.

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• Would a soft start installed on the AC remedy some of these start issues?

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• Hi Stan, yes, it does lower the starting-up wattage. You can pick a smaller generator + soft start; this is the most optimal combo.

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2. I am working on sizing a whole house back up generator where the biggest loads are a 5 Ton and a 2 Ton a/c units, doing a load calculation I’m coming up with a 24W/21W LP/NG generator. But I was worried about the starting amps of the 5 Ton? Isn’t 2.5 X the running amps?
For the rest of the loads I will be using load shedding.
Thank you

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• Hello John, you’re right, that starting amps are very high; you should include them in calculating the size of the generator. We’re sorry we can’t be of more help here.

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• Use a start cap to reduce starting current and extend compressor life

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• Using Soft Start like ICM you can lower inrush amps by 70%. 16kWt generator can handle both units and no light flickering. For 5 ton thatâ€™s \$225 and for 3 ton \$185. I think it worths spending \$400 on Soft Start

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3. What size generator can run a 3.5 ton central air with Lra of 109

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• Hello there, a 5,000-watt generator should be enough for a 3.5-ton unit.

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• For a 3.5 ton a/c unit the generator should be rated at 4 times the running load amps. Typically 18 amps for a compressor which means 72 start up (Peak) amps. 17,500 watt peak watts for a 3.5 ton central a/c unit. A/C compressors need a heck of a lot of power to start, that is why lights in the house dim.

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• This is the way I understand it as well. I had a kholer generator 17kw and it bared down starting a 2 ton Trane. Water cooled only for extended use. Air cooled is for a short weekend.

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4. I have a 5 ton ac and am looking at a 8kw genera with 10000 surge watts. Will that run my ac, 2 tvâ€™s and a fridge with a few lights that have fluorescent bulbs?

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• Hello Mark, 5 ton AC usually runs on about 5000 watts. 8kW generator with a 10k surge will be enough; TV + fridge + fluorescent lights require about 1000 W combined.

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• Good luck with that

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• Agreed, I have the 9500 with 12000 surge and it wont start my 5 ton a/c

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5. I got the Westinghouse wgen5300v it supposedly goes up to 6500. I have a 3.5 tone ac and it would not run it. I even put the gen on the same circuit as ac as to not add resistance of the rest of the house wiring and it did not have enough to get through startup. It would try and the outside fan would start to turn, the gen would bog down for a sec. I even sped up the motor but it wasn’t enough. I see other recomendations of 14kw plus. I wish there was a better way to figure it out without trial and error. Luckily wallyworld let’s you bring stuff back.

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• Hello Kip, the problem you’re experiencing is usually associated with start-up wattage. That’s the power rush you have to provide to start up the 3.5 ton AC; and it get-go past 6,500W. In many cases, a 6.5 kW generator can manage to start up a 3.5 ton AC, but as you’ve correctly pointed out, it’s a bit of a trial and error thing here.

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• As stated earlier in this blog, add a hard start capacitor to existing outside condenser setup and it should start up. Cost is around \$30 or less. Just plug it in.

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6. I am looking at a 15,000 watt portable generator ( generac) to run my 4 ton a/c an some other house hold product will it work???

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• Hello Wade, 15,000-watt generator is more than enough for a 4 ton A/C. After the start-up wattage surge, you can run several other household appliances as well.

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• Hi learnMetrics, I just bought a generac 8000e 8000 running watts with 10k surge watts. I want to run my 5 ton central ac 1 fridge, my laptop computer modem, 2tvâ€™s and my adt alarm system. And maybe a few fluorescent lights.is the generator big enough?

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• Hello Mark, 8,000W running watts will be enough for the 5 ton AC, and several appliances. The 10,000W surge wattage might be a problem; you would have to first start the AC alone (unplug everything else). That will most probably work; but it’s not 100% certain.

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• Your article clearly says a 7kw generator would be ample for a 5ton

• Hello Mark, yes, that’s for running an AC unit. The start-up wattage can be several times higher than the running wattage.

7. Hello, I have 4 ton AC with LRA of 109 / RLA 17.09. Will a generator with 12.5K surge watts and 9.5K running watts power the AC, fridge, and TVs?

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• Hello Tommie, 4 ton AC running at 100% output capacity will require about 5,000 W of power. With a 12.5 kW surge generator you can easily run a 4 ton AC as well as the fridge, TV, etc.

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• P = I x V. 109 locked rotor amps calculates out to 26,160 amps.

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• is that calc using 120V or 240V? In fact many ACs run on 230V…

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• 240V. So, to get 6000W at 240V you need 25 amps. 6000W = 240V * 25A.

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• 109LRA x 240v = 26,160amps. No one seems to address these amps. What generator can produce this?

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8. Hello, I have 5 ton 15 CEER AC with LRA of 152 / RLA 23.7. Will my generator with 12.5K surge watts and 9.5K running watts power the AC, fridge, and TVs?

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• Hello Bernie, yes, it the size of the generator is adequate.

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9. To all those reading these comments, just a rule of thumb……..never go over 75% of continued running wattage on small portable generators….so if its rated at 6000 continuous, figure 4500 constant load. Most, if not all, of these roll a round portable generators are Chinese built and not made for 100% duty cycle ( like running a central air conditioning system) Regardless of the brand name!!
It’s a whole different story when you get into the fixed/permanent mounted gensets

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10. I have a 6500 running / 8125 starting generator, I canâ€™t get my 4ton unit to run . 26.9 running amps.
It starts to turn the. Trips the 30 amp breaker on then generator – any suggestions . I considered disconnecting the power to the fan until the compressor kicks on.

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• Hello Scott, the 4 ton unit is on 220V? 8125W at 220V will draw 8125W / 220V = 37 amps. That will trip the 30 amp breaker, yes. You would require two 30 amp breakers. Now, if you don’t have them, that will be a problem. The compressor is the main electricity consumer and it needs a lot of amps. You can disconnect the fan but the fan only requires very few amps to run. It might solve the problem, but that’s very unlikely.

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11. I am looking to buy a portable generator for my home for back up power and would like to know what size to get to run the following: oil burner and circulating pump, 5 ton AC, well pump, refrigerator/freezer, 10 cu ft chest freezer, washer, dryer, 1 burner on range, 1.5K microwave, lights, garage door opener, television, laptop or desktop computer. I do not need to run everything at once. For example, I would not need to wash and dry clothes unless there was an extended power outage.

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• Hello Yvonne, that’s quite a lot of appliances. The rationale here is to sum up all the wattages of the appliances you want to run. These are running wattages, and you buy a generator that matches that wattage or surpasses it a bit. For example, 5 ton AC runs on 6,000 watts and you want to use it with a 1,500W washer, 500W chest freezer, and 3,000W of other appliances. That’s 11,000W total; you would need a 15,000W generator. Sorry if this is not the exact answer; it’s really hard to add up all the appliances’ wattages. Hope this helps a bit.

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12. I think most people who want to use a portable generator as a home backup only consider wattage without considering amps. Unless you buy a generator with a 50 amp outlet, you can probably forget using your AC unless you have a 1.5 – 2 ton unit. Even large generators have a problem with 4-5 ton units unless they’re equipped with either a kick start or soft start add-on.

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• Hello there, that’s a very good point.

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13. I see all the requirements to run A/C units, but not any to see how much is needed to run the heat strips in a central 3 Ton unit. I have a variable start fan, so is there a large startup draw for the heat strips? I have a 5 T and 3T. I can set them up to only run 1 at a time. Last winter was brutal with 7 days no power and sub freezing temps. Don’t want to live that nightmare again!

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• Hello Richard, you’re right. It’s much easier to see the running AC electric power requirements. Start-up wattage varies quite a bit from AC to AC. To start-up an AC you can require anywhere from 1.5 to 4 times the running wattage. You can calculate the generator size from that. Hopefully, the coming winter won’t be as harsh as the last one.

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14. It seems to me that even after my AC unit is started the first time, it will cycle on and off a few times per hour. So does the start-up wattage spike every time it cycles? If it does and my generator is rated just big enough to cover the start-up requirement, then I still have to manage (load shed) the other appliances in the house (refrigerators, etc…) every time the AC cycles. Correct?

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• Hello Victor, that’s correct. Every time the AC cycles on, it will draw its start-up wattage. You do have to account for all the loads accordingly.

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15. Hi,
Can you tell me the size generator I will need to start and run a 5 ton/20 seer AC? I wont be using it in conjunction with other high draw items (stove/HW heater/etc.)

Thank you!

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• Hello Matt, a 5-ton AC unit has a running wattage of about 6,000W. So that’s what size generator you would require to run the AC. However, the tricky part is the starting wattage. Starting wattage can vary from 12,000W to over 20,000W. You should check what starting wattage your AC has (it’s usually on the label) and size the generator according to that. You can also reduce that starting wattage by using a surge protector and thereby reduce the size of the generator you need.

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16. I have a 5 ton ac unit and a generator that has 8750 starting watts and 7000 continuous watts will that be enough to run the ac and the fridge an maybe a few lights

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• Hi Pablo, you are looking at about 6000W running watts for the 5 ton AC; you are left with 1000W for the fridge and maybe some lights. That’s all OK. The starting wattage might be a problem; a 5 ton AC can have over 10,000 starting wattage. In short, if the AC starts on this generator, you can run it along with the fridge and some lights.

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17. Folks, I have a 5-Ton AC at my residence. I purchased a 15000 Starting Watt/12000 Running Watt portable generator to power my house. I also installed a Micro-Air Soft Start Switch compatible to my 5-Ton AC unit for around \$300. My generator has no problem starting the 5-Ton AC unit as the Soft Start switch causes a delay between the fan and the compressor lowering the start-up amperage. Info is all on You-Tube.

I went further and installed an interlock switch at the service entrance panel which prevents line back feed and keeps our electrical linemen safe during power outages. Again all this info is on You-Tube.

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• Hi Gabriel, thanks for the input, this is very helpful.

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