In the forced-circulation type of hot-water system, a pump is used to force the water through the pipingThus, the flow is entirely independent of the difference in water temperature. Gravity hot-water systems arused mainly in small buildings such as homes and small business places.
Advantages of this type of system include:
1. Ease of operation.
2. Low installation costs.
3. Low maintenance costs.
Disadvantages include:
1. Possible water damage in case of leaks.
2. Rapid temperature changes result in a slow response from the system.
3. Properly balancing the flow of water to radiators is sometimes difficult.
4. Nonattendance when the heat-generating unit fails may result in a freeze-up.
5. Flow depends on gravity, and as a result, larger pipe sizes are required for good operation.
Forced hot-water heating systems require a pump that forces the water through the piping system.
Limitations of flow, dependent on water-temperature differences, do not exist in this type of system. It may be of either the one- or two-pipe variety. In two-pipe systems, either direct or reversed returns or up-feed or down-feed mains may be used. The path of the water from the boiler into and through the radiator and back again to the boiler is almost the same length for each of the radiators in the system. It is common to use one-pipe forced-circulation systems for small- and medium-sized buildings when hot water is used as the heating medium.
Advantages of forced circulation include:
1. There is rapid response to temperature changes.
2. Smaller pipe sizes may be installed.
3. Room temperatures can be automatically controlled if either the burner or the flow of water is
thermostatically controlled.
4. There is less danger of water freeze and damage.
Disadvantages include:
1. All high points must be vented.
