The definition of a hot water coil HVAC system is a type of heating system that uses hot water to transfer heat to a space. Hot water coils are typically used in commercial and industrial applications, but can also be used in residential settings. Hot water coils are usually made of copper or aluminum and are designed to transfer heat from a hot water source to the air in a space. The hot water is circulated through the coil, which absorbs the heat and transfers it to the air. Hot water coils are a cost-effective way to heat a space, as they require less energy than other types of heating systems. Additionally, hot water coils are easy to install and maintain, making them a popular choice for many homeowners. Hot water coils are also more efficient than other types of heating systems, as they can provide a more consistent temperature throughout the space.