Can a generator run a central air unit for emergency how many watts does a 2.5 ton unit use?

Answer 1

The simple answer is yes.

The long answer requires info from you.

There are two power requirements, running and starting. AC Compressors require an enormous boost of power to get them started, sometimes 5-7 times the running power. To find your running watts, we need to know the SEER rating, usually listed on the air handler. Newer units must be at least 11 SEER. 1 ton = 12,000 btus, so you have 30,000 btus. Divide this by the seer, and that's your running wattage. Even if your seer is only 10, that's only 3000 watts. Seems like not much.

Now look at the outside unit to find the LRA. This is the locked rotor amp draw, which is a good indicator of the required amperage to start the unit. For example, my unit runs on 16 amps, and has an 88 amp start requirement. Now you can see how huge the start amps are. So a tiny 2.8 ton ac unit will need an 18,000 watt generator to get going!

What you will need to do is install a "hard start" device on the outside unit. Its basically a large capacitor used to get the compressor going without the need for huge amps. Some claim they can cut the start amps in half. They cost $20-50, have 2 wires and are easy to install, can be installed and left in all the time, prolongs the life of the compressor and also prevents your lights from dimming when the ac kicks on. Make sure to get a properly sized one, as too big will cause big problems.

The only way to know for sure is to install the hard start kit and then have someone actually measure the amp draw. Good luck.