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Noisy or Banging radiators

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Noisy or Banging radiators

Postby TenantNet » Sun Jan 07, 2018 12:52 pm

First, search the forum for "noisy banding radiors" and also google the terms.

Published: March 1, 1981

A KNOCKING or noisy radiator or one that does not heat all the way across is annoying and can also be inefficient, wasting energy because heat is not being delivered uniformly.

Regardless of whether the system is steam or hot water, the radiators are used are basically similar and will fall into one of two broad categories: cast iron radiators that have hollow sections through which the hot water or steam flows, or tube-and-fin convector radiators that consist of copper tubes that have metal fins around the outside to provide increased radiating efficiency when hot water flows through the pipes and heats them. The newer convection type or fin-type radiators are not normally used in steam systems, but cast iron radiators are used in both steam and hot-water systems.

In a steam system, there is only one pipe connected to the radiator, and steam enters through this single pipe to heat the radiator. In the process the steam condenses (it loses its heat to the metal) and forms water, which then runs back out through the same pipe and inlet valve until it finally runs all the way back to the boiler. There it is reheated and the whole process starts over again.

That is why all steam pipes must slope downward toward the boiler; if they don't, water will be trapped in the pipe and this can result in banging or hammering noises every time the steam comes up - the incoming steam tries to force its way past the trapped water and this causes the water to bang around or ''hammer'' against the walls of the pipe.

Although structural settling or recent alterations can result in pipes no longer sloping properly for rapid drainage of condensed water, more often than not hammering or banging noises in a steam system takes place in the radiators themselves, rather than in the piping that leads to it. One common cause of this is a radiator inlet valve that is not all the way open - on steam radiators the valve should be either all the way open or all the way closed.

Another frequent cause of banging noises in a steam system is that the radiator is not sitting level, or is pitched the wrong way. The radiator should slant slightly toward the valve so that water that accumulates on the bottom will flow out easily, as shown in the accompanying drawing. If placing a spirit level on top of the radiator indicates that it is not slanting toward the valve, then place a couple of thin blocks of wood under the legs at the far end to increase the angle of pitch.

When radiators in a hot-water system develop banging or hammering noises the problem is most often due to trapped air that cannot get out. Air gets into the system from the fresh water that is periodically added to the system (usually automatically) to replace water that evaporates or leaks out. The trapped air keeps the radiator from filling all the way with hot water, sometimes causing a pounding noise and almost always keeping the radiator from heating all the way across.

To cure this, radiators in a hot-water heating system have to be bled periodically - trapped air must be eliminated by opening special vents or tiny valves provided for this purpose. They are usually opened with either a screwdriver or a special key, and are generally at the top of the radiator near one end. You open the vent till all trapped air escapes, then as soon as water starts to flow out freely close it immediately.

In some single-pipe hot-water heating installations where the radiators are all in a single loop, there may not be a vent on each radiator; the vent may be located at the end of the run, or in a higher location somewhere in the system. If you cannot find the vent, ask your local heating contractor to show you where it is and how to bleed it when this becomes necessary.

Steam radiators also have vents at the end opposite the inlet valve, but these are self-bleeding so they can let air escape automatically each time steam starts to enter - otherwise the radiator will not get hot all the way across (trapped air will keep steam out of the farthest sections).

If a steam radiator does not get hot all the way across, unscrew the vent valve completely and clean it out by soaking in vinegar - or, better yet, replace it entirely with a new one. Replacement units are available in many hardware stores, as well as in most plumbing supply houses.
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