A Hot-Water Systems Inspection is designed to ensure the heating system is operating properly, at maximum efficiency. A hot-water system operates on the principle of circulation and recirculation. Basically, water is heated in a boiler and then transmitted through pipes to radiators located throughout the house. The hot water gives up some of its heat to radiators, while the cooler water continues to flow back to the boiler where it is reheated and recirculated.
In a hot-water system, the boiler, distribution piping and all the radiators are entirely filled with water. When heated, this water expands and increases its overall volume, therefore all these systems must be equipped with an expansion tank to temporarily store the increased water volume.
When the system is shut and the circulating water cools, the volume decreases and draws the water back from the expansion tank. If there is no tank, excessive pressure could build up in the system and potentially rupture the distribution pipes and fittings.
The water that circulates within the heating system operates under a pressure normally ranging between 12 and 22 psi. As the water is constantly recirculating there is no need for additional water, however an automatic water-feed device is still provided with all systems, as a precautionary measure.
An automatic water-feed device is a pressure-reducing valve. The water supply to the boiler is drawn from the house water supply , but considering that the house supply pressure normally ranges from 30 to 60 psi, it must be reduced before being introduced into the boiler. The reducing valve is typically preset by the manufacturer to 12 psi.
Hot-Water Systems Inspection – Gravity and Forced Systems
Hot-water heating systems come in two basic types: gravity and forced systems, a classification based on the means by which the water circulates within the system.
Similar to the gravity warm-air heating system, the gravity hot-water system is not efficient and often non-responsive to changing demands for heat. Because of such shortcomings, it is no longer installed in new construction, but it may still be found in many older homes.
As the water is heated, it becomes lighter than the cooler water and tends to rise. The system is filled with water, so as the hot water rises, it displaces the cooler water and forces it to return to the boiler for reheating, thus inducing circulation. In order to keep the resistance to flow at a minimum, the size of the distribution piping is quite large (about three inches in diameter) compared to the distribution piping in a forced system (about one inch in diameter).
Generally, hot-water and steam systems are equipped with automatic pressure-relief valves that discharge when the pressure exceeds 30 psi and 15 psi, respectively. In an open gravity hot-water system, however, this relief valve is unnecessary because if the pressure builds up to a point where it exceeds the design pressure, the water will simply discharge through the overflow pipe in the expansion tank.
With a forced hot-water system, the size of the boiler is very small compared to the one in a gravity system. Apart from the size of the boiler, you can easily recognize a forced hot-water system is you see a circulating pump in the distribution return pump just before the connection to a boiler.