A new water heater means hot showers come back on schedule, no more cold-water surprises during the dishwasher cycle, and a working tank that is not rumbling from the basement. The swap itself usually takes a plumber half a day, sometimes a full day if you are also changing from a tank to a tankless unit or moving the location. Most of the cost is the unit and labor split roughly down the middle, so the bill feels bigger than a single appliance.
Late spring and early fall are the sweet spots. Plumbers are less slammed, hot weather has not driven emergency calls, and you avoid the winter rush when a cold tank is an urgent crisis. Booking in a slow window often gets you a better quote and a faster appointment.
The 0% for 18 months on purchases and balance transfers from date of account opening is a deadline, not free money. If a balance is still sitting on the card when month 18 ends, interest starts accruing at the card's regular purchase rate, and you will owe it back on the standard schedule. Pay it off on time and the plan works exactly as drawn up.