procedures. Check the simplest and more obvious items before progressing to the other checks.

Q15. With warm-air systems, the amount of heat reaching each room is determined by what two factors?

Q16. What are the four airflow designs of gas-fired furnaces?

Q17. What safety device on gas-fired heating equipment reacts to the operation of the pilot flame?

Q18. What device shuts off the gas supply when the temperature inside the heating unit becomes excessive?

Q19. What are the three internal areas of an oil-fired furnace?

Q20. What device is the nerve center of the heating control system?

Q21. What are the two most commonly used types of thermostats?

Q22. A steam-atomizing burner requires a steam pressure of what range for atomizing?

Q23. Electrode adjustments should always be set on burners according to what publication?

Q24. What instrument is used to determine the percent of CO₂ produced by combustion?

DOMESTIC HOT-WATER HEATING AND HOT-WATER BOILERS

Learning Objective: Identify types of hot-water boilers, their fittings and accessories, and their operation.

The Navy uses both cast-iron and steel hot-water boilers as sources of heat for domestic hot-water systems in residences and other buildings. Small hot-water heaters heat the hot water for domestic and for limited industrial uses.

Hot-water boilers come in many shapes and sizes. They are constructed with a firebox for burning fuel and have provisions for passing the hot gases over the heat-absorbing surfaces of the boiler. In most cases, baffles guide the gases over the most effective route. These baffles also retard the flow of the gases from the furnace, so water can absorb as much of the heat as possible. Both ends of the boiler have openings for cleaning the boiler tubes and for washing the interior of the boiler. Since most boilers are stationary units permanently installed at the site, they have specified fittings and accessories for a specific heating job. Some boilers, however, called package boilers, are complete units, including fittings and accessories. These boilers are normally mounted on skids so they can be moved to different sites.

This accounts for the term package boiler. Package boilers usually have the same accessories and controls as the comparable stationary type of hot-water or steam boiler. Cast-iron boilers are seldom used as package boilers because of the danger of cracking the boiler sections during transportation.

Cast-iron hot-water boilers vary in size from small domestic units to moderately sized units capable of developing 31 through 98 horsepower. These boilers are usually constructed of several sections joined together by push nipples (round pieces of metal pipe tapered at both ends). Pipes, known as header connections (fig. 4-58) ordinarily connect the boiler sections.

Cast-iron boilers normally do not have brick settings. Usually, the only bricks used with these boilers are those that are sometimes used as a base for the boilers. In most cases, the bases are made of cast iron. Square sectional cast-iron boilers are similar to the typical unit shown in figure 4-59. This boiler consists of a front and rear section and a number of intermediate sections, depending on the size of the boiler. The sections are connected on each side at the top and bottom either by push nipples or by an outside header. When nipples are used, these sections are held firmly together by rods and nuts.

The boiler has a separate base that does not contain water and, therefore, requires a floor of fireproof construction. Boilers that have water in their bases are referred to as wet-bottom boilers. These boilers are relatively small water units that may be installed on floors constructed of combustible materials. This method of installation, however, is not desirable.

The construction of square sectional boilers is ordinarily such that the sections can be taken through regular-sized doors for assembly inside the boiler room. This is a distinct advantage from the standpoint of both installing new equipment and replacing broken sections. Cast-iron boilers resist the chemical action of corrosive agents much better than steel boilers.

The disadvantage of cast-iron hot-water heating boilers is the danger of the sections cracking or breaking when improperly handled or fired. 4-38