They can be either off-on or proportional (a mixture of off and on, or an ability to control the amount of flow). ... If you need to drain your system for winter use, you usually need a vacuum breaker; if you need to drain quickly, a vacuum breaker is definitely necessary. ... Domestic water heater systems often use an electronic controller that takes temperatures, time of day, and other factors into account.
|Title||:||Solar Power Your Home For Dummies|
|Publisher||:||John Wiley & Sons - 2011-02-09|