In my experience with that.... I would say you had a 100 amp service. You would need to add a double pole single throw breaker,It should be 30 or better. If wired for 220. Count the amps on the breakers that are there now and see if they add up to 100 or more..Or look at the main breaker and see what it says on the switch. If it's more?Then you would have a 200 amp panel. You could add the breaker then..