Boiler and Furnace Conversion

Sometimes it becomes necessary to convert an existing boiler or fur­nace to another fuel. This is usually the case when the fuel for which it was originally designed has become too expensive relative to oth­ers or does not meet the desired level of efficiency. During the early 1950s, when coal was becoming more and more expensive as a domestic heating fuel and before oil and gas burners were offered as integral parts of heating units by manufacturers, converting boilers and furnaces was a much more widespread practice than it is today.

A number of manufacturers have made available gas-fired and oil — fired burners specifically designed for boiler and furnace conversions. It would be impossible within the space limitations of this chapter to cover all the different models of conversion burners offered by these manufacturers. Consequently, this chapter will emphasize all the ramifications involved in converting a boiler or furnace from one fuel to another instead of examining the specifications and operating characteristics of one or more conversion burners.

Initially, most coal burning furnaces and boilers were converted to oil or gas. This was done not only for convenience (the coal — burning appliances required more hands-on maintenance) but also for heating efficiency and lower energy costs. Tighter environmen­tal regulations covering oil storage tanks (the tanks would often develop leaks as they became older) and the sudden rise in heating oil costs as the result of the 1970s oil crisis motivated a widespread conversion from oil to gas.

Before deciding to convert from one fuel to another, consult with a technician from a reputable heating dealer about the ramifica­tions, practicality, and safety factors involved in converting. You may be able to lower energy costs by increasing the insulation levels in the home and by replacing the furnace or boiler with a high­efficiency appliance burning the same fuel. That is, better results might be obtainable by upgrading the system instead of converting.

If there is no alternative to converting from one fuel to another, then operating safety must be a primary consideration, followed by heating efficiency and energy costs. There are some potential safety hazards involved in converting from an oil-fired furnace or boiler to a gas-fired one. If the technician making the conversion is knowl­edgeable about these hazards, then proper precautionary measures

Can be taken to ensure safe operation. When using gas burners in a converted oil heating system, consider the following:

• Gas burners require greater amounts of excess combustion air than an oil burner does to ensure safe operation. Lower amounts can lead to the production of odorless, colorless, and deadly carbon monoxide gas. ALWAYS install a carbon monoxide gas detector near a gas combustion burner.

• Gas burners produce much more water vapor than oil burners. These water vapors will condense on the walls of the chimney and flue as they cool. This condensed water is acidic and can damage the chimney mortar, flue surfaces, and even the heat­ing appliance itself. Consequently, some state and local codes have mandated the upgrading or replacement of the chimney and flue along with the installation of a gas-conversion burner. Upgrading the chimney involves lining it with an acid-resistant material. It is often necessary to install a new vent system meeting the requirements of gas-burner combustion.

• The gas burner flame pattern must match the size and shape of the combustion chamber, which was originally designed for an oil burner flame. The two kinds of flame have different sizes and characteristics. If this is not taken into consideration when the gas conversion burner is installed, the gas flame may contact the internal surfaces of the combustion chamber, resulting in the production of carbon monoxide gas.


ALWAYS measure the carbon monoxide emission of a gas conversion burner immediately after it is installed. According to the ANSI Standard, CO emissions must be below 0.03 of the exhaust gases.

Preparation for Conversion

Before constructing a combustion chamber and installing a burner, the heating system should be carefully checked for defects and cleanliness. A boiler or furnace in need of repairs will not give satis­factory results after the burner is installed. Be certain that all flue passages are cleaned so that the maximum amount of heat gener­ated is absorbed by the boiler. Soot and ash are good insulators, and both are always undesirable.

All doors should fit tightly, and all other openings or cracks should be tightly cemented shut. The stack from the furnace to the chimney should have tight joints. Dampers should not close off more that 80 percent of the cross-sectional area of the stack. Stacks should be inspected for leaks and obstructions of any kind.

Remove the old fuel-handling parts (e. g., the coal-handling parts in a coal-fired furnace or boiler) and thoroughly clean the interior surfaces, removing all soot, scale, tars, and dirt.

Any cracks in the heat exchanger should be repaired or replaced. On boilers, any water leaks should be sealed, broken gauges replaced, and loose boiler doors repaired or replaced. Air leaks along the floor should be grouted.

No positive catches should be used on firing doors. File off any catches so that the firing door will open easily to relieve pressure. A spring-loaded door holder is recommended.

If a conversion burner with a direct spark ignition system is installed, no provision need be made for top venting or horizontal or downdraft furnace. Check the local codes for further information.

Figure 16-1 illustrates some of the typical problems encountered when converting a coal-fired boiler to oil. It is highly doubtful that

Boiler and Furnace Conversion







Figure 16-1 Boiler problems to be remedied before converting and installing an oil burner.

A boiler would have all these problems at the same time, but for your convenience they are included in the illustration to serve as a reference.

Basic Combustion Chamber Requirements

An essential requirement for combustion chambers is that the flame be in the presence of refractory materials so that it will not come into contact with any of the relatively cold heating surfaces of the boiler.

When the flame is burned in suspension in a combustion cham­ber of refractory material, the refractory walls will reflect the heat back into the flame and thereby increase its temperature. This increase in flame temperature due to reflected heat greatly increases the rapidity of combustion and thereby makes possible the burning of every particle of fuel with the zone combustion.

The combustion chamber walls should be high enough so that the flame will not come in contact with the relatively cool walls of the boiler. At the burner end, the refractory wall need not be higher than the grate line of the boiler.

Finally, a well-designed combustion chamber should provide rapid heating at the beginning of each firing cycle.

Combustion Chambers for Conversion Gas Burners

Conversion gas burners are designed for firing into a refractory lined combustion chamber constructed in the ashpit of a boiler or furnace. It is recommended that built-up combustion chambers used for this purpose be constructed of 2300°F insulating firebrick and cemented with insulating firebrick mortar.

Recommended minimum wall thicknesses and floor areas of these combustion chambers are based on the maximum rated Btu capacity (Table 16-1).

The height of combustion chamber walls will usually be deter­mined by the grate line. Build the side and front walls about 2 inches above the grate line. The grate lugs and base of the water legs of boilers should be covered by about 3 or 4 in to avoid heating sec­tions that may be filled with sediment. Carry the back wall one or two brick courses higher than the side or front walls and allow it to overhang in order to deflect hot gases from impingement on the heat exchanger surfaces. Use a hard firebrick for the overhang section, because the high-velocity gases moving against it tend to erode a softer brick.

Table 16-1 Recommended Minimum Wall Thicknesses of Combustion Chambers Using Conversion Gas Burners

Input Btu/h

Floor Area Sq. In

Width and Length




X 15




X 16




X 17




X 18




X 20




X 21




X 22




X 27




X 31




X 35




X 33




X 36




X 32




X 34




X 36




X 44




X 50




X 55




X 60




X 65




X 68


2V2 insulating firebrick plus backup of 1V2 or more loose insulation

4V2 insulating firebrick plus backup of 1V2 or more loose insulation

Recommended Minimum Wall Thickness

подпись: recommended minimum wall thickness

Recommended Minimum Floor Construction

2 Vi insulating firebrick plus V2 insulating material recommended by firebrick manufacturer.

4Vi insulating firebrick plus Vi insulating material recommended by the firebrick manufacturer.

подпись: recommended minimum floor construction
2 vi insulating firebrick plus v2 insulating material recommended by firebrick manufacturer.
4vi insulating firebrick plus vi insulating material recommended by the firebrick manufacturer.

Courtesy Magic Servant Products Co.

If the combustion chamber is to be placed directly on the floor of the ashpit, a layer of suitable insulating material or refractory brick recommended by the firebrick manufacturers (V2-in minimum thickness) should underlay the combustion chamber. Ordinary brick may be used in the floor of the combustion chamber. Ordinary brick may be used in the floor of the ashpit. The remain­ing open space should be filled with vermiculite or some other suit­able loose insulation.

Combustion Chambers for Conversion Oil Burners

A combustion chamber for a conversion oil burner should be constructed of lightweight 2000°F insulating firebrick. With lightweight refractory materials, there is no long smoky delay waiting for the firebox to reach the temperature necessary for com­plete combustion.

Different types of combustion chamber construction are shown in Figures 16-2 and 16-3. The shape of the combustion chamber will be determined by the shape of the boiler or furnace.

The combustion chamber area (space) is equal to the inside width of the boiler times the length times the distance from the combustion chamber floor to the crown sheet. It is recommended that 1 ft3 be provided for each boiler horsepower, or 3 ft3 per gph oil-fired.

The floor area of the combustion chamber should be based on 100 in2 per gph of oil (see Table 16-2 and Figures 16-4 and 16-5). The minimum side wall height should conform to the recom­mended measurements listed in Table 16-2.

An overhang in the form of stepped corbels will deflect hot gases from impingement on the heat exchanger surfaces, increase combus­tion chamber temperatures, and thereby promote good combustion.

Boiler and Furnace Conversion







подпись: protect /water leg


подпись: rear firing Boiler and Furnace Conversion

When flue outlet and target wall are on same end, use corbel and locate combustion chamber for maximum contact of products with crown sheet

подпись: when flue outlet and target wall are on same end, use corbel and locate combustion chamber for maximum contact of products with crown sheetFigure 16-3 Combustion chambers for boilers. (Courtesy Stewart-Warner.)

High-flame-retention burners provide an intense flame that elim­inates the need for refractory combustion chambers above 3.0 gph and has greatly reduced the need for such chambers in the 1.0- to 3.0-gph range.

Table 16-2 Combustion Chamber Floor Area

Dimensions (100 in2 per gph)


Round I. D.

Rectangular W X L

Nozzle Height N

Min. Side Height H



7" X 8"





8" X 9"





9" X 91/2"





9" X 11"





10" X 11"





101/2" X 12"





11" X 12"





12" X 121/2"





13" X 131/2"





14" X 14"





14" X 16"





14" X 18"



— 3/8

+ 1/4





Boiler and Furnace Conversion



■_ •



■ : — v


RJ. ri’5


Boiler and Furnace Conversion

Figure 16-4 Side view of combustion chamber. (Courtesy Stewart-Warner.)



P­r Ь-


‘ + 1/4

— 3/8 — 0





подпись: lLit ■■ ■


Figure 16-5 Top view of combustion chamber. (Courtesy Stewart-Warner.)

Construction Materials

The construction materials used in building combustion chambers for conversion burners should consist of the best grade of insulating firebrick and a good, high-temperature refractory mortar.

Insulating firebricks are available in different standard shapes and sizes for residential, commercial, and industrial applications. Their primary function is to provide a lining capable of withstand­ing the high temperatures in furnace and boiler combustion cham­bers, flues, chimneys, stacks, and fireplaces. To function in these high temperature environments, firebricks have upper-limit melting points that range from 2800°F (1540°C) for a brick made of fire­clay to 4000°F (2200°C) for one made of silicon carbide.

Firebrick materials

The materials used in firebricks should make them capable of withstanding not only high temperatures, but also slag chem­icals and spalling (i. e., flaking) under temperature changes. Firebricks are made from fire clay or kaolin, silica (silicon car­bide), alumina, and magnesite (magnesia).

• Clay firebricks. Firebricks made from fire clay or kaolin are the most common type, but they are expensive and not good insulators. The principal advantage of the clay firebrick is that it creates a thin, lightweight combustion chamber wall. This results in a quick rise of temperature that produces fuel savings. On the down side, clay firebricks have a relatively low melting point of 1600°F (871°C).

• Silica firebricks. Silica firebricks retain their strength at high temperatures and do not react with ash, which makes them resistant to deposits. On the other hand, they are subject to spalling (flaking). They are also very expensive.

• High alumina firebricks. High alumina firebricks are capable of withstanding both high load deformation levels and high temperatures.

• Magnesite (Magnesia) firebricks. Magnesite firebricks resist the effects of alkalis.


Modern firebricks are asbestos free. If you have stocks of older firebricks containing asbestos do NOT use them, Contact a local EPA office for instructions about their safe disposal.

Firebricks can be machined or drilled at the factory in custom shapes and sizes to meet the requirements of specific applications. To mention only a few possibilities, custom firebricks are available with machined grooves, tapers, radii, tongue-and-groove edges, and drilled holes.

Insulating firebricks are produced in different grades to meet the requirements of specific applications. The temperature use limits are an important factor in making a selection. Another important factor to consider when selecting a suitable firebrick is its mean temperature; that is to say, the temperature at the midpoint of the firebrick. These and other specifications for each grade of firebrick are provided by the refractory material manufacturer.

Always use the refractory mortar furnished or recommended by the brick manufacturer for cementing the insulating firebrick. The mortar should be thinned to the consistency of a very thick cream before it is used. The usual method for applying the mortar is to dip each brick into it and set the brick in place as you lay each course.


Additional support is possible by using metal anchors project­ing from the metal casing.

The shape of the bricks is also important, with arch or circled brick where 4[6]/2-inch wall thickness is preferred. The mortar-filled joints between the bricks should be not more than Vs inch.

The insulating firebricks are usually backed by a second, separate insulating layer, which may consist of one of the following materials:

1. Common brick

2. Magnesia block insulation

3. Hard firebrick

4. Expanded mica products (e. g., vermiculite or zonolite)

5. Dry sand

6. Dry sand mixed with an expanded mica product

The spaces between the outer edges of the firebrick should be filled with high-temperature refractory mortar and small pieces of firebrick to obtain firm construction and prevent infiltration of vapors through the wall.

Building a Combustion Chamber

Figure 16-6 illustrates the construction of a typical custom-built combustion chamber. The steps involved in constructing this cham­ber are as follows:

Boiler and Furnace Conversion

3. Dip the bottom and sides of brick B in the binder and place it in a circular position on the combustion chamber floor. You should start at the back and work toward the front of the chamber.

4. Follow the same procedure with the rest of the bricks in the tier (i. e., those on the same level as brick B).

5. When the tier is finished, tighten it in position with bands suitable for this purpose.

6. Fill behind the first tier with rock wool.

7. Install top tier D in the same manner described in steps 1 through 5; however, use only one band to tighten it.

8. Cap the chamber with a mixture of 3 parts refractory mortar and 1 part fire clay, and trowel smooth.

9. Place metal sleeve F in the opening, and cement it tightly in place.

10. Insert the draft tube in metal sleeve, and pack with loose rock wool or a suitable insulating material.

Boiler and Furnace Conversion

Figure 16-7 Combustion chamber for an older cast-iron boiler.

Figure 16-7 shows an old, round, cast-iron boiler that has been converted to oil. Note the height of the combustion chamber wall. The procedure for setting up the oil burner to the combustion chamber is illustrated in Figure 16-8.

Ventilation Requirements

If the existing boiler or furnace is located in an open area (basement or utility area) and the ventilation is relatively unrestricted, there should be sufficient supply of air for combustion and draft-hood dilution. On the other hand, if the heating unit is located in an enclosed furnace room or normal air infiltration is effectively reduced by storm windows or doors, then certain provisions must be made to correct this situation. Figure 16-9 illustrates the type of modification that should be made in a furnace room to provide an adequate supply of air. As shown, two permanent grilles are installed in the walls of the furnace room, each of a size equal to 1 in2 of free area per 1000 Btu/h of burner output. One grille should be located near the ceiling, and the other near the floor.

If the boiler or furnace is located in an area of particularly tight construction, the heating unit should be directly connected to an


Boiler and Furnace Conversion


Figure 16-9 Air openings necessary to supply air for combustion when furnace is installed in an enclosed room.

Plaster up well with furnace cement.

подпись: plaster up well with furnace cement.

Mm….. V///M…….

подпись: mm v///m.

Figure 16-8 Procedure for setting up burner to combustion chamber.

подпись: figure 16-8 procedure for setting up burner to combustion chamber. Boiler and Furnace Conversion

Brick up almost flush with end of burner nose piece.

подпись: brick up almost flush with end of burner nose piece.

When plastering and finishing front, put newspaper over air tube to keep all spotless.

подпись: when plastering and finishing front, put newspaper over air tube to keep all spotless.

Outdoor source of air. A permanently open grille sized for at least 1 in2 of free area per 5000 Btu/h of burner output should also be provided. Connection to an outside source of air is also recom­mended if the building contains a large exhaust fan.

A conversion burner equipped with a spark ignition system is not suited for use in furnaces or boilers located in areas subjected to sustained reverse draft or where large ventilating fans operate in combination with insufficient makeup air. There is always the danger of drawing flue gases into the structure. (See Installing a Conversion Gas Burner in this chapter.)

Flue Pipe and Chimney

The flue pipe is a pipe connecting the smoke outlet of the furnace or boiler with the flue of a chimney (Figures 16-10 and 16-11). It should not extend beyond the inner liner of the chimney and should never be connected with the flue of an open fireplace. Furthermore, flue connections from two or more sources should never enter the chimney at the same level from opposing sides.

Flue pipe should be constructed from corrosive resistant metal and be designed with as few sharp turns as practical. The straight — est and shortest possible passage should be provided for the exist­ing flue gases.

Do not extend flue pipe

Boiler and Furnace Conversion

Figure 16-10 Chimney and flue connection with horizontal draft

Hood. (Courtesy Mid-Continent Metal Products Co.)

Boiler and Furnace Conversion

Figure 16-11 Chimney and flue connection with vertical draft hood.

(Courtesy Mid-Continent Metal Products Co.)

Pitch the flue pipe with a rise toward the chimney of at least Vi in per foot. At approximate intervals, fasten the flue pipe securely with sheet-metal screws to prevent sagging.

Masonry is recommended for the construction of chimneys (pre­fab chimneys are also found suitable). Outside metal stacks are gen­erally unsuitable for oil-fired burners.

The ordinary chimney must be at least 3 ft higher than the roof or 2 ft higher than any ridge within 10 ft of the building in order to avoid downdrafts.

Aside from adapting the furnace or boiler for a conversion burner, changes must also be made in the passages formed by the heating surface.

Extra-large flue passages are not suited to the high-temperature flue gas encountered with oil. In boilers having these large flue pas­sages, baffling must be used to slow down the high velocities of the extra-hot gases; otherwise unburned particles of oil may lodge on the heating surface, resulting in carbon deposits. Because carbon is an excellent insulator, the efficiency of the heating surface is low­ered whenever it collects. (See the following section.)


Baffling is a type of obstruction designed to deflect and regulate the speed of flue gases. Baffles are especially necessary for round boil­ers and furnaces constructed so that the flue passages are almost direct from the firebox. Furthermore, boilers designed for burning coal are usually provided with relatively large flue passages, which are not normally suited to the higher flue gas velocities encountered in oil firing.

Baffling will, in most cases, help to overcome the inefficient operation resulting from the usual excessively high stack-gas tem­peratures. In such instances it is advisable to experiment with vari­ous methods of baffling as shown in Figure 16-12.


Any baffling of the flue passages that prevents efficient opera­tion of the burner should not be done.

Another form of baffling is a corbel, or stepout, arrangement of the brickwork of the rear wall, forming a target wall that the flame strikes and is curled back to prevent short circuiting.

Gas Piping and Piping Connections

Figures 16-13 and 16-14 illustrate the piping connections necessary for two different models of gas-fired conversion burners.


All local codes and ordinances take precedence over the instructions in the burner manufacturer’s installation manual. If there is no manual available, the installation of the burner must conform to the manufacturer’s instructions, the regula­tions of the National Fire Protection Association, and the pro­visions in the latest editions of the National Electrical Code (ANSI/NFPA70) and the National Gas Code (ANSI Z223.1).

Boiler and Furnace Conversion

Boiler and Furnace Conversion


подпись: boiler sections Boiler and Furnace ConversionSTACK






Figure 16-12 Various methods of baffling for sectional cast-iron boilers.


Boiler and Furnace Conversion Boiler and Furnace Conversion

Boiler and Furnace Conversion

Figure 16-13 Pipe connection for a conversion gas burner

(with pilot light). (Courtesy Mid-Continent Metal Products Co.)

No matter what type of gas-fired conversion burner you decide to use, it must be allowed to develop its rated capacity. This can be accomplished by making certain the burner is connected to a gas supply containing sufficient pressure.

In addition to providing for a gas supply with sufficient pressure, the following recommendations are also offered:

1. Provide for a separate gas-supply line of 1-in pipe size direct from the meter to the burner (ample for runs up to 60 ft long).

2. Install an intermediate regulator if the line pressure exceeds 13.5-in W. C (water column).

3. Connect the burner to the piping as shown in Figures 16-13 and 16-14.

Boiler and Furnace Conversion



Boiler and Furnace Conversion


Figure 16-14 Pipe connection for a conversion gas burner (without

Pilot light). (Courtesy Mid-Continent Metal Products Co.)

4. Install a manually operated main shutoff valve 4 to 5 ft above the floor on the vertical pipe.

5. Make certain the pipe is clean and free of any scale.

6. Use malleable iron fittings.

7. Remove all burrs and scales from the pipe and clean it before installing it.

8. Do not tap off from the bottom of horizontal runs when branching from a pipeline.

Gas Input Setting

The gas conversion burner illustrated in Figure 16-13 is manufac­tured to operate on natural gas, but kits are available for converting to propane. A very important factor to be considered when

Installing these burners is a correct determination of the gas input setting, which should be based on the following two factors:

1. The heating rate of the structure

2. The rated maximum input of the burner

The heating rate of a structure is essentially the amount of warm air that the heating unit must deliver to heat it adequately. Methods for calculating the amount of heat required (i. e., the heating rate) are described in Chapter 4, “Sizing Residential Heating and Air Conditioning Systems.”

Another important factor to consider is the rated maximum input of the burner. The gas input cannot exceed this rating. If the burner maximum input of the burner is below the required mini­mum of heat indicated by the heating rate, then the burner is inad­equate for your needs.

The gas input setting for a natural gas conversion burner is regu­lated by the spud (orifice fitting) size and the pressure regulator. A burner is commonly shipped with three different spud sizes, one for each of three capacity ranges (high, intermediate, and low; Table 16-3). The capacity range is changed by using a different spud siz­ing. After the appropriate spud has been installed, the final gas input setting is made by adjusting the pressure regulator. Be sure to read the burner manufacturer’s installation instructions carefully.

A propane gas conversion burner operates directly on 11-in wg gas supply pressure as determined by the propane-tank regulator. The portion of the combination control on the standard natural gas burner is blanked off with a plate provided in the propane conver­sion kit. Two spuds are provided: a minimum-size main spud and a pilot spud. The main spud must be redrilled for the required capac­ity (see Table 16-4).

Table 16-3 Spud Sizing for Natural Gas


Capacity Btu/h

Spud Size






" W. C.

Manifold Pressure)


Drill No.








# 4






Table 16-4 Spud Sizing for Propane


Capacity Btu/h

Spud Size

11" W. C.

Manifold Pressure

Drill No.























Courtesy Mid-Continent Metal Products Co.

Installing a Conversion Gas Burner

The conversion gas burners illustrated in Figures 16-13 and 16-14 are used to convert coal-fired or oil-fired central heating plants to gas. They are adaptable for use in forced-warm-air furnaces, grav­ity (updraft) furnaces, or boilers (Figures 16-15 through 16-18).

In addition to the basic combustion chamber requirements (see the appropriate section in this chapter), the following recommen­dations must be followed when installing a conversion gas burner.

1. The diameter of the burner opening into the combustion chamber must not be oversize. If the opening is oversize, slip the stainless steel sleeve (included with the burner) over the nozzle and fill in the remaining space with refractory cement.

2. Position the end of the burner nozzle so that it is at least 1 inch short of the inside surface of the combustion cham­ber. Never allow the nozzle to extend into the combustion chamber.

3. If the burner nozzle is too short to reach the combustion chamber, it may be lengthened with an extension tube.

4. Check the burner ports and pilot before permanently setting the burner in place, and remove any foreign matter blocking the openings.

Starting a Conversion Gas Burner (with Pilot Light)

This section covers the starting of conversion gas burners equipped with pilot lights. Before attempting to start this type of burner, the piping should be checked for leaks. The basic procedure for doing this is as follows:

1. Shut off all other gas appliances (gas water heaters, etc.) that tie into the same system.

2. Turn on the main shutoff valve (Figure 16-13).

3. Turn valve dial A to OFF (Figure 16-13).

4. Turn on gas pressure to the gas supply line.

5. Watch the meter test dial.

If the meter test dial shows no movement for at least 5 minutes, it is safe to say that there are no leaks in the piping. Movement of the meter test dial, however, means that you must locate the leak (or leaks) before starting the burner. The soapsuds test is a simple and effective method for doing this.

Boiler and Furnace Conversion

Figure 16-16 Downdraft forced-warm-air furnace equipped with a conversion gas burner. (Courtesy Mid-Continent Metal Products Co.)

The gas line must be purged before starting the burner. To do this, the following steps are recommended:

1. Disconnect the pilot tubing.

2. Depress valve dial A as far as it will go, and turn it counter­clockwise to PILOT (Figure 16-13). Do not release the dial at this point.

3. With valve dial A still fully depressed; lock the dial in position by engaging the lighting latch B (Figure 16-13).

4. Allow the air to escape until the gas line is completely purged (which will be indicated by gas replacing the air issuing from the pilot connection). Caution: Never purge the gas line into the combustion chamber.

5. Turn off valve dial A (depress and turn clockwise).

6. Reconnect the pilot tubing.

Boiler and Furnace Conversion


Figure 16-17 Downdraft suspended heater equipped with a conversion gas burner. (Courtesy Mid-Continent Metal Products Co.)

After you have checked the piping for leaks and have completely purged the gas lines, you are now ready to start the burner. First add a few drops of oil (#20 SAE oil is recommended) to the burner motor bearings. Then, check the setting of valve dial A. At this point, it should be turned to OFF (see step 5 in the purging proce­dure just described).

You are now ready for the initial startup procedure, which is accomplished as follows:

1. Set the main air shutter at approximately one-quarter open.

2. Turn on the main line switch.

3. Set the room thermostat above room temperature (this will cause the burner motor to start).

4. The burner motor should be allowed to run for about 5 min­utes to ensure complete purging of the combustion chamber.

Boiler and Furnace Conversion

Fill doors with suitable mineral fiber insulating material

Remove latch from firing door and install spring closer.

Seal stainless steel sleeve with suitable mineral fiber insulating material

2300°F insulating firebrick

Conversion gas burner

^ ^…….. V ^………………. ^^

Seal door opening ^ Common brick or V2 min.


Figure 16-18 Hot water or steam boiler equipped with a conversion

Gas burner. (Courtesy Mid-Continent Metal Products Co.)

5. Shut off the burner motor by adjusting the thermostat setting below room temperature.

6. Fully depress valve dial A and turn it counterclockwise to PILOT. Keep it depressed.

7. Lock valve dial A in its depressed position by engaging the lighting latch B.

8. Light a match and hold the flame under the igniter valve and at igniter slot C while at the same time depressing button C for at least 10 seconds.

9. Release the lighter button. The pilot should now ignite. If it does not, then repeat Step 8 above.

10. After the pilot has been burning for at least 1 minute, release valve dial A and turn it counterclockwise to the ON setting.

Starting a Conversion Gas Burner (Pilotless)

Most of the instructions given in the previous section for starting a conversion gas burner equipped with a pilot light will also apply here. The major difference is the use of direct spark ignition rather than a pilot flame.

The basic procedure for starting a pilotless conversion gas burner is as follows (Figure 16-14):

1. Check the piping for leaks.

2. Bleed (purge) the gas line.

3. Set the air shutter about three-quarters open.

4. Depress the valve dial and turn it on the ON position.

5. Turn on the main line switch.

6. Set the room thermostat above the room temperature. This should cause the burner motor to start. If it does, burner igni­tion should occur after 30 seconds.

7. If the burner fails to light, turn off the main line switch and then turn it on again.

8. Readjust the air shutter for a quiet, soft flame. The flame should be blue at the burner, changing to orange at the tips.

9. Start and stop the burner several times with the thermostat to check its operation.

Servicing a Conversion Gas Burner

Always be sure that the manual gas valve and burner switch are turned off before attempting to service a gas burner. Never attempt to remove any parts for service before taking this precaution.

In direct spark ignition burners, the nozzle and electrode assem­bly can usually be removed as a unit. For example, the nozzle-and — electrode assembly of the Economite Model DS20A conversion gas burner can be completely removed in the following manner:

1. Remove the burner backplate.

2. Disconnect the pipe union.

3. Remove the curved orifice pipe.

4. Withdraw the nozzle assembly.

5. Disconnect the electrode leads.

6. Remove the unit.

The nozzle-and-electrode assembly can be reinstalled by revers­ing steps 1 through 6. When reassembling, make certain the orifice pipe enters the nozzle casting.

With the nozzle-and-electrode assembly completely removed, you are now in a position to inspect and clean it. Check the elec­trode for insulator cracks and evidence of serious burning.

Removal of the burner backplate also provides access to the motor and blower, motor relay, low-voltage transformer, and termi­nal board. These can be removed as a unit for servicing, but you will have to disconnect the terminal board and unplug the electrical pass-through fitting to do this. The following service may be required for this unit:

1. Cleaning of the blower wheel.

2. Cleaning the motor air vents.

Does the motor run without further burner sequencing taking place? This may indicate trouble in the centrifugal interlock switch. Some burners are provided with removable motor end caps to provide ready access to the centrifugal switch. If this should be the case, remove the cap and clean the contacts by bur­nishing. The contacts must be open when the motor is not operat­ing. If necessary, the burner motor can be removed and replaced as follows:

1. Remove the blower wheel.

2. Remove the retainer clips at the motor grommets.

3. Pull the motor out of the brackets.

4. Repair or substitute a new motor.

5. Place motor in brackets.

6. Make certain grommets fit well in the bracket and replace retainer clips.

7. Replace blower wheel.

The sealed motor relay and low-voltage transformer nor­mally do not require servicing. They should be replaced when defective.

Check gas lines and valves for leaks with the soapsuds test. Never use a flame to locate a gas leak. If the leakage occurs around the valve, the valve seat may need cleaning. Disassemble the valve, clean the seat, and reassemble it. If the valve malfunction is due to causes other than the seat, replace the entire valve.

Replace the gas pressure regulator if it fails to maintain a con­stant pressure. On the conversion gas burner illustrated in Figure 16-14, the regulator is part of a combination valve (in this case, a Robertshaw 24-volt combination gas valve), but it is designed so that it can be replaced without replacing the entire assembly.

Pressure adjustment required for setting intermediate capacities can be accomplished as follows:

1. Remove the adjustment screw cap.

2. Take a screwdriver and turn the adjustment screw counter­clockwise to reduce pressure.

3. Measure the pressure through the manometer connection adjacent to the outlet tapping.

Conversion gas burners equipped with a pilot light require inspection and servicing of the following:

1. The pilot orifice size will depend upon the type of gas used. For the conversion gas burner illustrated in Figure 16-13, the pilot orifice will have a diameter of 0.018 in for natural gas and 0.012 in for propane.

2. Set the end of the burner nozzle at least 1 inch short of the inside of the combustion chamber (see Figures 16-15 through 16-18). It must not be set flush with the chamber or be allowed to extend into the chamber (the pilot is often snuffed out in such cases by recirculated flue products).

3. Check for a high or low gas pressure. If over 7 inches W. C., reset the pilot adjustment (see Figure 16-13) to reduce the size of the pilot flame and to increase the heat on the thermo­couple.

The thermocouple and pilot-safety section of the main valve should be tested to determine whether they are operating efficiently. The testing procedure is as follows:

1. Turn the burner switch to OFF.

2. Allow the combustion chamber to cool and the pilot light to operate for at least 5 minutes.

3. Turn off the pilot and listen for a “click” from the main valve.

4. If the “click” of the main valve is heard more than 30 seconds after you have shut off the pilot, then both the thermocouple and the pilot-safety section of the main valve are operating efficiently.

5. If the “click” occurs less than 30 seconds after you have shut off the pilot, then either the thermocouple or pilot-safety sec­tion of the main valve is faulty.

6. Test the thermocouple by disconnecting it from the main valve and checking it with a millivoltmeter. Under normal conditions (i. e., when heated by a standby pilot), it should develop at least 15 millivolts.

7. If the thermocouple develops at least 15 millivolts but the main valve “click” still occurs less than 30 seconds after you have shut off the pilot, the pilot-safety section is probably malfunctioning.

8. The thermocouple may also be tested while still connected to the valve (a closed-circuit connection) by using an adapter to connect the millivoltmeter. Under normal operating condi­tions, the thermocouple should develop at least 7 millivolts and the valve 4 millivolts.

The wiring diagram for a conversion gas burner equipped with a pilot light is shown in Figure 16-19. The installation and service instructions from most manufacturers will include a wiring diagram for the burner. Study it carefully before servicing or making repairs.

Oil Tanks and Oil Piping

Local codes and the National Board of Fire Underwriters will pro­vide information for the installation of oil tanks and piping.

In oil piping, copper tubing is commonly used for suction and return lines. A 3/8-in OD minimum is recommended for lines under 30 ft long. If the suction and return lines exceed 30 ft, then V2-in OD copper tubing is recommended.

Other suggestions for the installation of the oil storage tank and piping include:

1. Use a good-quality pipe joint compound and make your pipe thread connections as tight as possible.

2. Keep the lines between the oil tank and burner as straight as possible (avoid kinks and traps).

3. Keep the connections in the return line to a minimum.

4. Check tubing flares and connections for air leaks (an indica­tion of a poor seal resulting from improper meeting).

The two basic types of piping arrangements are: (1) the single­line system and (2) the two-line system. These two piping arrange­ments are distinguished from one another primarily by the location of the oil storage tank with respect to the oil-fired conversion burner.

24-volt main automatic


Valve with flame failure interlock controlled by a thermocouple

Figure 16-19 Wiring diagram for a conversion gas burner equipped

With a pilot light. (Courtesy Mid-Continent Metal Products Co.)

Motor with internal blower interlock switch GROUND

подпись: motor with internal blower interlock switch ground


подпись: relay with 24 v coil

Series connect all operating and/or limit controls in this circuit—

2 wire line voltage

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подпись: series connect all operating and/or limit controls in this circuit—
2 wire line voltage
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подпись: raa<;>5lh-t.

I 1120 V — 60_HZ — 1 PH

1——————— ‘ NEUTRAL L2


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1 ' neutral l2
fused disconnect


подпись: low voltage thermostat Boiler and Furnace Conversion


подпись: l1A single-line piping arrangement is used only where the oil stor­age tank is located above the level of the oil burner. No return line is necessary. The oil is taken from an outlet in the bottom of the storage tank and fed by gravity to the burner. The slope of the pipe should be gradually downward (approximately */2 in per foot) to a point directly below the burner connection. This downward slope in the line is designed to prevent the formation of air pockets and bubbles. The installation of a shutoff valve in the line is recom­mended.

A two-line piping arrangement is required where the oil storage tank is buried at a level below that of the burner.

Installing a Conversion Oil Burner

Conversion oil burners should be installed in accordance with the provisions of the National Fire Protection Association and local codes and regulations. Local codes and regulations will always take precedence. Read these regulations and the manufacturer’s installa­tion instructions before making any attempt to install the burner.

If the furnace or boiler was originally designed to burn solid fuel and the ashpit is not used as a part of the combustion chamber, the ash door should be removed to prevent the accumulation of vapors in the ashpit. If removal of the ash door is not feasible, then some other means of bottom ventilation must be provided.

Before installing the burner, check the condition of the boiler or furnace. It must be in good condition or repair. The flue gas pas­sages and combustion chamber must be tight against leaks. Reseal or reset the sections of a cast-iron boiler or furnace. Replace any damaged parts. The boiler or furnace should also be as clean as possible before installing the burner.

A combustion chamber must be provided that is in accordance with the specifications of the burner manufacturer. Read the appro­priate sections in this chapter (e. g., Basic Combustion Chamber Requirements) for more information.

If you are satisfied that the boiler or furnace with which you are working satisfactorily meets the conditions mentioned in the previous paragraphs, then you are ready to install the conversion oil burner. The basic steps recommended for installation are as follows:

1. Position the burner on its mounting flange or pedestal so that the burner air tube is flush with the inside surface of the com­bustion chamber front wall. Do not allow the burner air tube to extend into the combustion chamber.

2. Adjust the burner tube on pedestal-mounted burners so that it pitches downward about 1V2 in. Any fuel in the burner tube will then drain into the combustion chamber.

3. On flange-mounted burners, the distance from the flange to the end of the air cone will depend upon the requirements of each installation. Remove the air cone before installing the flange.

4. The distance between the center of the nozzle and the floor of the combustion chamber must be correct. If it is too close, it will result in flame impingement and carbonization. On the other hand, a nozzle placed too high will result in excessive flame noise and poor combustion.

5. The fuel pump should be adjusted for the oil pressure recom­mended by the manufacturer.

6. Adjust the air supply to the burner with the air inlet band. Rotate the air inlet band to the required position (the one

Which will deliver the smallest amount of air and still main­tain clean combustion), and secure it in position.

7. Make certain the size and spray angle of the nozzle is correct for the installation (check the UL rating plate).

8. Install the nozzle, and check the electrode tip position in accordance with the manufacturer’s instructions.

9. Prime the fuel pump (see the manufacturer’s instructions).

Starting a Conversion Oil Burner

Before attempting to start the oil burner, you should first carefully read the manufacturer’s instructions. Unfortunately, these are not always available on older heating installations. If this is the case and you do not possess the necessary expertise to operate the burner without an instruction manual, it is strongly recommended that you call a professional for services.

Always test the oil lines for possible leaks and make the neces­sary repairs before starting the oil burner. Consult the manufac­turer’s instructions for bleeding the fuel pump. The bleed valve on the fuel pump is designed to facilitate air purging, cleaning, and priming. See Chapter 1, “Oil Burners” of Volume 2 for additional information about fuel pumps.

Check the electrical wiring diagram (if one exists) to make cer­tain that the burner is correctly wired. Problems with an oil burner can often be traced to incorrect wiring. All wiring must be in accor­dance with the National Electrical Code as well as local codes, standards, and regulations.

It is important to make certain that the primary and limit con­trols are operating properly. Test the primary control by first removing the motor lead from the burner and then energizing the ignition circuit by throwing the switch. If the primary control is operating properly, the ignition will shut off within 2 minutes after the switch is thrown. If the ignition fails to shut off after 2 minutes, the primary control should be replaced.

Check the fuel level in the oil storage tank. There must be enough oil to operate the burner. Open both oil valves (at the oil storage tank and at the boiler or furnace).

You must have an adequate air supply for efficient combustion. The basic ventilation requirements (see Ventilation Requirements in this chapter) must be provided for when installing the oil burner. It is also important to determine whether the secondary air setting is correct. If smoke or soot is present when the oil burner is operating, the air setting must be corrected.

If all the suggestions in the previous paragraphs have been fol­lowed and the necessary adjustments or repairs made, the oil burner can now be started. The procedure for doing this is basically as follows:

1. Make certain that all controls have been set in normal starting position.

2. Make certain that the oil valve in the oil supply line is open.

3. Set the room thermostat 10° above the room temperature.

4. Check the reset button on the primary control to make certain it has been reset.

5. Open the air control band on the burner to about half open.

6. Throw the main electrical switch to ON. The burner should now start, ignite, and burn. If it does not, recheck steps 1 through 5. If you still experience difficulty in starting the burner, consult Troubleshooting Oil Burners in Chapter 1, “Oil Burners” of Volume 2.

7. Allow the oil burner to operate for about 15 minutes, then shut it down and give it time to cool off. After it has cooled off, restart it to be sure it operates properly on a cool start.

While the oil burner is operating (step 7), you should take the opportunity to make a number of tests. Check the fuel-pump pres­sure with an oil pressure gauge. These should be factory set. Adjust the air control band on the burner until 0+ smoke is obtained with a smoke tester. Adjust the draft control (if necessary) to obtain at least 0.02 in W. C. of draft over the fire.

Servicing a Conversion Oil Burner

Protecting the oil burner motor from unnecessary wear is extremely important. At least once a year (but not more than three times a year), preferably at the beginning of each heating season, place about 10 drops of #20 SAE oil in each oil port of the burner motor. After you have oiled the burner motor, clean the fuel strainer and change the oil-filter cartridge. Clogged fuel strainers are a common source of trouble. In rotary- and gun-type oil burners, these compo­nents are usually located either at the point at which the oil line con­nects to the tank or at the oil line connection to the burner. Follow the manufacturer’s instructions for removing the fuel strainer, and clean it with a stiff wire brush or a blast of compressed air.

Be sure that you are using the correct weight of oil. If the oil is too heavy, the burner motor will start, but it may fail to establish a flame. Continued use of the wrong oil may cause damage to burner components.

Soot should be periodically removed from the burner and com­bustion chamber. Commercial soot removers are available for this purpose. When burning out a layer of soot, take care not to ignite a soot fire in the chimney. This could be very dangerous because it may lead to the igniting of combustible materials near the chimney. The hard layer of carbon that frequently forms on the bottom of the firepot in burners should also be removed.

Other servicing recommendations for conversion oil burners are as follows:

1. Check the furnace or boiler for possible air leaks. Any that are found should be sealed (a refractory mortar is recommended) because they interfere with combustion efficiency.

2. Check the burner nozzle in gun-type burners. If it is dirty, remove and clean it according to the manufacturer’s instructions.

3. Check the position of the electrodes in rotary — and gun-type oil burners. They should be positioned near, but out of, the direct spray of the oil.

Troubleshooting Oil and Gas Conversion Burners

Operating problems, their symptoms and causes, and the suggested remedies for oil and gas conversion burners are covered in Chapter 1, “Oil Burners” and Chapter 2, “Gas Burners” in Volume 2.

Posted in Audel HVAC Fundamentals Volume 1 Heating Systems, Furnaces, and Boilers