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Steam Boiler Tutorial

Most of your steam problems start when the customer wants a price on a new steam boiler. The larger number of steam boilers installed are over sized. This practice causes short cycling of the boiler that reduces the efficiency and also creates system problems. 

The proper way to size a steam boiler is measure the existing radiation. Convert all the radiation to sq. ft. of steam or commonly called EDR. Most of the time do not add any thing for piping or anything else. There are a few things to keep in mind. If the horizontal mains in the basement are not insulated insulate them. (See chart for BTU loss of steel pipe ). After sizing all the radiation grab the manufacturers brochure and select the boiler from the sq ft of steam available. (Brochure)

   Proper steam boiler operation starts with the near boiler piping. The piping of steam boilers has not changed in the last 100 years or so. The piping diagrams must be followed to the tee for a good operation. Always use iron pipe above the water line of the boiler. Copper may be used below the water line if you choose. A few reasons we do not want copper above the water level although it is not against national codes, is the steam can leach the copper from the piping and these copper molecules get back into the boiler and a galvanic reaction occurs. This will shorten the life of the boiler. Another reason is copper pipes expand (see expansion of pipes) far more than black iron pipe. This will stress the joints more than screw or welded pipe joints. All the piping around the boiler has names. Let's get familiar with these terms.

 

Riser to Main System      Boiler Riser      Header      Equalizer      Water Line      Condensate Return      Hartford Loop
2" Explanation      24" Explanation      See Actual Manufacturers Drawing
Another Idea - Dropped Header
 
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Riser to Main System
The system riser as it is normally called carries the steam from the header to the system. The steam at this point should be dry and moving quickly. If there are more than one main the boiler has to connect to there should be multiple system risers.
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Boiler Riser
The boiler riser(s) carry the steam produced in the boiler to the header. There may be one riser or multiple risers. If using multiple risers they should all connect to the header before any system risers are connected to the header.
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Header
The header is part of the heart of the near boiler piping. The purpose of the header is to collect all the steam from the boiler, which will include some water, and move it to the system risers allowing the water to separate from the steam. The steam will rise up in the pipe and the water will stay on the bottom of the pipe. As the steam gets to the system risers the steam will go up and the water and a small amount of steam will stay in the header.
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Equalizer
The equalizer does exactly what it says. It will equalize the pressure between the header, supply side of the boiler, and the return side of the boiler. As the header builds steam pressure most of the steam goes out the system risers. The balance pushes into the equalizer. The equalizer has a water volume as high as the water level in the boiler. The steam pressure pushes down on the water in the equalizer. If there is 1 lb of pressure in the boiler and header there is one lb of pressure pushing down on the water in the equalizer. This creates equal pressure on the supply and return of the boiler. When the supply and return have the same pressure, the water will stay in the boiler. 
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Water Line
This is more commonly known as the Normal Water Level (NWL). This is where the boiler manufacturer would like to see the boiler water maintained for the best operation. The manufacturer will always give this dimension from the bottom of the boiler to the NWL desired. Many steam boilers have automatic water feeder installed on them. The thought is we no longer have to check the water level. This is incorrect. The automatic water feeder does not maintain the water level at the NWL. It maintains the water level at a minimum water level. The automatic water feeder is for emergency use only. It will add water as needed to maintain a minimum water level if you are not home or forgot to check the water level lately. You should check and maintain the water level at the manufactures suggest NWL dimension.
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Condensate Return

The condensate return is the pipes that carry the condensate; steam, which condensed back into water, back to the boiler.  There are two types of condensate return pipes. They are known as DRY returns and WET returns. The only difference is the location of the pipes. If the return pipe is above the water line it is called a dry return. If the condensate return pipe is below the water line it is a wet return. The wet return is under the water level all the time, which becomes loaded with debris over many years. These wet returns are known as the garbage dump of the system. It is a good idea to replace them when a new steam boiler is installed is a residential application.

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Hartford Loop

The hartford loop was first designed as boiler protection so if the wet return would spring a leak all the water would not drain out of the boiler and cause a dry fire. Dry firing the boiler means there is no water in the boiler and the boiler continues to fire. This will crack the boiler and require a boiler replacement. Never add water to a dry fire condition unless the boiler has had ample time to cool down. Adding water to a very hot boiler may cause physical injury or damage to the boiler and or property. A hartford loop should be installed on all steam boilers unless the boiler has a pumped return from a condensate pump or boiler feed unit. Never install check valves in the return lines of residential steam boilers with dry or wet returns.

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2" Distance on Hartford Loop

The 2" distance shown on the drawing for the hartford loop is a critical distance. This is the distance from the normal water level (NWL) is to the top of the elbow on the hartford loop. Follow the manufacturers instructions in the I & O manual. If in doubt use the top of the elbow. If this horizontal distance becomes too high or too low it can affect performance or create noises. The horizontal piping from the tee or wye to the hartford loop should be as close as possible. If that connection becomes too long it also could cause noises.

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24" Distance

The 24" distance shown in the drawing is the distance from the normal water line (NWL) to the centerline of the header. This is a minimum distance. The higher the header the better. Our concern is to make the steam as dry as possible. Longer pipes from the boiler to the header will allow more water to drop out of the steam as it travels up the boiler raiser to the header.

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Dropped Header

 

Dropped headers may be used when the installation will have low ceilings or anytime you want drier steam. The boiler risers will go up the required minimum 24" and elbow horizontal and elbow back down. The more piping and fittings the steam goes through the drier the steam gets.

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