Gas water heaters, electric water heaters and solar water heaters are now the most widely used units for domestic hot water. They all have advantages in providing hot water.
Heat pumps for heating and cooling buildings can be divided into four main categories depending on their operational function: Heating-only heat pumps, providing space heating and/or water heating.
Heat flows naturally from a higher to a lower temperature. Heat pumps, however, are able to force the heat flow in the other direction, using a relatively small amount of high quality drive energy