I would like to know..why is it the ac guys problem everytime someone adds to their house and they receive a high electric bill.
Can we place the blame on the framer,the insulation guy,or
even the home owner themself who now has more lights and tv to leave on thruout the house.
1800 new + what existing 1500 from before..I too would say the 350 dollar bill not bad.
Build a castle and pay a king ransom.
What about water heater(s)?
Gas or electric?
Was one added in addition or larger one
to replace existing?
If gas won't matter-
Electric wtr htr's like electricity alot,
I'd check T-stat & settings on h2o htr.
have the electrican pop the circuit breaker panel cover and total up all the loads with the A/C off!then have him read the condenser disconnect outside with it on.that will narrow it down and until the season changes you will notice the difference on that bill.