"Understanding Your Home" by Building Inspector Mark Visser
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One-pipe system
The single-pipe system has a single pipe or main which supplies the heated water to the radiators or convectors and also returns the cooled water to the boiler.


Two-pipe system
This system has two mains. The heated water is supplied to the radiators or convectors through the supply main, and the cooled water is returned to the boiler through a separate return main.

Distribution pipes.
Most piping problems occur at the connection to the radiators and not in the piping itself. The pipes are costly to replace and should be checked periodically for rust and leakage.



Hot Water or Hydronic Heating Systems
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Hot water system. Hydronoc heating. Expansion tank. Circulation pump. Pipe insulation.

Hot water systems use a boiler to heat water and can be fueled by gas, oil or electricity. The combustion process in a hydronoc or hot water circulating system is virtually identical to that found in a forced
warm air system. A hot water system is different because the heat is distributed through water pipes instead of ducts.
Modern hydronic systems usually employ a flow-through type of heat exchanger. This consists of a number of finned heat exchanger tubes connecting two headers. This system is generally used with finned convector type radiators which transfer the heat to the rooms.
Electric boilers. The central boiler uses electrical elements to heat the water. The heating elements are immersed directly in the water that is being heated (like the heating coil in an electric kettle). The boilers are compact, some are no larger than a suit case. Where space is limited, the boiler can be installed on a wall or even in a closet.
Expansion tank.
The expansion tank in a hydronic heating system is partly filled with water. As the water is heated, it expands. The purpose of the tank is to store the extra volume of water created by expansion. Water and air eventually will mix and 'fresh' water has to be added.
Circulation pump.
It is possible that at times you may hear a thumping noise when the pump goes on. This is usually caused by a water-logged expansion tank (see above) or by air in the distribution system in which case the radiators or convectors have to be bled. Click here for more information about the air bleed valve.

Pipe insulation
The distribution pipes are often insulated in the basement area to prevent heat loss before they reach the radiators or convectors. Asbestos pipe insulation can still be found in many older homes. Friable asbestos is a health hazard and should be encapsulized or removed. Never attempt to do this yourself but call a licensed contractor. Click here for more information on asbestos

Compact gas boiler

One-pipe system

Two-pipe system

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