Hydronic Questions

Hydronic System Thermosiphoning
A flow control or flow check valve prevents gravity flow or thermosiphoning of system water when the circulator is not in operation. It has a weighted internal plug that is sufficiently heavy to overcome the buoyancy of upwardly migrating hot water. The flow control valve allows the system water to flow in one direction when the circulator supplies system pressure. These valves are particularly useful when the boiler provides domestic hot water especially in warmer weather.

When feeding another zone when zoning with circulators, a separate flow-check is used in each circuit to prevent thermosiphoning. It also will eliminate backward flow of water from an active circuit through an inactive circuit. Flow check valves are not required for zoned circuits using a motorized zone valve.

Tankless Coils versus Indirect Storage Tank
The two main hydronic methods employed to provide domestic hot water involve a boiler with a tankless coil or a boiler with an indirect storage tank. Each has its advantages and disadvantages. To determine the best alternative depends on many factors which must be evaluated prior to selecting the system. Among these are the number of people in the household, number of showers, the type of system being replaced, etc.

Tankless Coil
As the name implies, this method of heating domestic hot water does not use a storage tank. Typically, it consists of a finned copper coil immersed in the boiler system water to instantaneously transfer heat from the boiler system water to potable water flowing through the coil. The quantity and rate of heat absorbed by the domestic water depends on its flow rate and the temperature of the boiler system water. The flow rate can vary according to the water pressure. Numerous piping methods and controls are readily available to compensate for these variables. Cost and simplicity are its main advantages.

Indirect Storage Tank
This method of heating DHW utilizes a storage tank in conjunction with a hot water boiler. Heat is exchanged between the hot boiler system water and the cold potable feed water. Large quantities of water are heated, stored and available on demand. The boiler replenishes the hot water supply during standby periods. Hot water is available at flow rates limited only by the piping and fixtures, and in amounts relative to the tank volume. Typically water can be heated two to five times faster than a direct fired water heater. This high recovery rate is its main advantage.