The answer to 'water heater vs' is that water heaters and furnaces/boilers have different functions, installation requirements, and costs. Water heaters are dedicated to providing hot water for your home, while furnaces and boilers are used for whole-home heating. Water heaters are generally less expensive to purchase and install, but have higher ongoing energy costs. Furnaces and boilers typically have higher upfront costs but can be more energy-efficient for whole-home heating.
The best option for your home depends on your specific hot water and heating needs, energy efficiency goals, and available space. A professional HVAC technician can help evaluate your home and recommend the most suitable system.