Backup Power Series: UPS, Generators, and Air Conditioners

white wind turbine against a clear blue sky.

Apr 12, 2023 by Brent Earls

We’re going to conclude our series on backup power and UPS by addressing things external to the UPS (you can check out our previous blog here). This mostly includes environmental concerns like how UPS, generators, and air conditioners can either work together, or disrupt your IT environment.


One of the mistakes that people often make with UPS is oversizing the batteries to try to get extremely long runtimes – without considering anything else. UPSs are great at running electronics for short durations, but for long run times they aren’t the most efficient method.

Generally speaking, if you’re seeking more than an hour of runtime from your UPS, you should probably be looking at a generator. Those can run for (essentially) ever with proper care. For long term operations they are much more efficient over a UPS, as a bank of dozens and dozens of batteries for an hour of runtime isn’t a great option.

That’s not to say you can’t make a UPS handle that need. If you have a smaller environment and you can’t afford a generator, a UPS can definitely accommodate the load. There are diminishing returns on having JUST a UPS the larger your environment though. Having a UPS for short term power lasting long enough for a generator to kick in, is a great option. The UPS can also condition the power coming out of the generator to make it cleaner and more server-friendly.

Air Conditioners

The other major environmental consideration that often comes up in this discussion is cooling. How long can your server room run without air conditioning? 5 minutes? 45 minutes?

This is very important, because if you size your UPS to run the environment for an hour, but the temperature gets to 120 degrees in 10 minutes, you won’t get the runtime you expected. If you’re at the office when it happens, you can obviously open the door to the server room and put a box fan in the door, but again, what happens when the power goes out in the middle of the night, can you get there in time?

The natural thought here is:

“So, we need to put the AC on the UPS too,”

But that’s not a great idea.

As we mentioned in one of the earlier blogs, some devices are very efficient at using power, and their Volt-Amps and Watts are the same and some aren’t. Air conditioners fall in the category of ‘aren’t’.

Air conditioners do very dirty things to electrical circuits. That’s why even in your home, with a direct connection to the grid, the air conditioner makes the lights dim. You don’t want that dirty power consumption right next to your sensitive servers on your UPS, not to mention that heavy and dirty consumption means the UPS has to be extremely oversized to accommodate. So, what’s the proper option?

If you have enough servers that the room is going to overheat, but you need extended runtime without grid power, there’s really only one answer – a generator.

How UPS, Generators, And Air Conditioners Work Together

Generators come in many forms – Natural Gas, Propane, and Diesel being the most common. Regardless of that choice, having a generator allows for UPSs to be sized more appropriately for just the servers, with a short runtime. The generator will be online within just a few minutes, and can take care of recharging the UPS and powering the air conditioner so everyone’s happy.  The single most important thing with a generator, however, is that it also needs regular testing and servicing. Most generator failures are from lack of servicing that allows the diesel fuel to lose its potency.

We know this is a lot to take in, but your Mirazon experts are on hand ready to help you take control of your backup power and UPS, in whatever way you need.

Complicated and confusing?  Reach out with questions by contacting us, call 502-240-0404 or email us at

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