There are two main types of water heaters: tankless and traditional tank-style. Tankless water heaters are more energy-efficient and provide an endless supply of hot water, but they are typically more expensive to purchase and install. Traditional tank-style water heaters are less expensive upfront, but they have a limited supply of hot water and are less energy-efficient.

The size of the water heater you need will depend on your household's hot water usage. You can determine your household's hot water usage by considering factors such as the number of people in your home, the number of bathrooms, and your daily hot water usage. The most used sizes for water heaters range from 30 (1-2 family size) – 80 gallons (5+ family size).

The fuel type you choose for your water heater will depend on several factors, including the availability of fuel in your area and your energy preferences. The most common fuel types for water heaters include natural gas, propane, and electric. Natural gas and propane are typically less expensive than electric, but electric water heaters are often more energy efficient.

The lifespan of a water heater will depend on several factors, including the type of water heater, the quality of installation, and the level of maintenance it receives. Traditional tank-style water heaters typically last 10-15 years, while tankless water heaters can last up to 20 years with proper maintenance.

The cost of purchasing and installing a water heater will depend on several factors, including the type of water heater, the size of the unit, and the complexity of the installation.