Go to rheem.com and look up their model# nomenclature. It can usually be found by looking at the spec sheet for any of their products, in your case a heat pump. That is if you don`t have the installation/operation manual for your unit, if you do happen to have that it`s on page 1 or 2.
2
2.5
4 ton
five ton
5 ton
two ton
3 tons
3 ton
3ton
3 TON
Your first set of numbers gives you the tonnage, so this is a 2 ton; your "4" number represents a 460-volt electrical requirement
2.5 tons. 1 ton =12,000 btu so 30,000 btu=2.5 tons. The 30 in the model # denotes btu of the unit in 1000`s.