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 Chapter 7 Heating and Environmental Control

I. Introduction

II. Definitions

III. Fuels

IV. Central Heating Units

V. Fuel-Burning Procedures and Automatic Firing Equipment

VI. Refractory

VII. Heating Systems

VIII. Domestic Hot Water Jack Stoves (Coal Stoves)

IX. Hazardous Installations

I. Introduction

The function of a heating system is to provide for human comfort. The variables to be controlled are temperature, air motion, and 

relative humidity. Temperature must be maintained uniformly throughout the heated area. Field experience indicates a variation 

from 6 to 10? F from floor to ceiling. The adequacy of the heating device and the tightness of the structure or room determine the 

degree of personal comfort within the dwelling.

Coal, wood, oil, gas, and electricity are the main sources of heat energy. Heating systems commonly used are steam, hot water, 

and hot air. The housing inspector should have a knowledge of the various heating fuels and systems to be able to determine their 

adequacy and safety in operation. To cover fully all aspects of the heating system, the entire area and physical components of the 

system must be considered.

II. Definitions

A Anti-flooding Control - A safety control that shuts off fuel and ignition when excessive fuel accumulates in the appliance.

B Appliance:

1 High-heat - a unit that operates with flue entrance temperature of combustion products above l,500?F.

2 Medium heat - same as high-heat, except above 600?F

3 Low heat - same as high heat, except below 600?F.

C Boiler:

1 High pressure - a boiler furnishing pressure at 15 psi or mole.

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2 Low pressure -(hot water or steam)-a boiler furnishing steam at a pressure less than 15 psi or hot water not more than 30 psi.

D Burner - A device that provides the mixing of fuel, air, and ignition in a combustion chamber.

E Chimney - A vertical shaft containing one or more passageways.

1 Factory-built chimney - a tested and accredited flue for venting gas appliances, incinerators and solid or liquid fuel-burning 

appliances.

2 Masonry chimney - a field-constructed chimney built of masonry and lined with terra cotta flue or firebrick.

3 Metal chimney - of metal field-constructed chimney.

4 Chimney Connector-A pipe or breeching that connects the heating appliance to the chimney.

F Clearance - The distance separating the appliance, chimney connector, plenum, and flue from the nearest surface of 

combustible material.

G Central Heating System - A boiler or furnace, flue connected, installed as an integral part of the structure and designed to 

supply heat adequately for the structure.

H Controls:

1 High-low limit control - an automatic control that responds to liquid level changes and pressure or temperature changes and 

that limits operation of the appliance to be controlled.

2 Primary safety control - the automatic safety control intended to prevent abnormal discharge of fuel at the burner in case of

ignition failure or flame failure.

3 Combustion safety control - a primary safety control that responds to flame properties, sensing the presence of flame and 

causing fuel to be shut off in event of flame failure.

I Convector - A convector is a radiator that supplies a maximum amount of heat by convection, using many closely-spaced metal 

fins fitted onto pipes that carry hot water or steam and thereby heat the circulating air.

J Conversion - a boiler or furnance, flue connected, originally designed for solid fuel but converted for liquid or gas fuel.

K Damper - a valve for regulating draft. Generally located on the exhaust side of the combustion chamber, usually in the chimney 

connector.

L Draft Hood - a device placed in and made a part of the vent connector (chimney connector or smoke pipe) from an appliance, 

or in the appliance itself, that is designed to (a) ensure the ready escape of the products of combustion in the event of no draft, 

back-draft, or stoppage beyond the draft hood; (b) prevent backdraft from entering the appliance; (c) neutralize the effect of stack 

action of the chimney flue upon appliance operation.

M Draft Regulator - a device that functions to maintain a desired draft in oil-fired appliances by automatically reducing the 

chimney draft to the desired value. Sometimes this device is referred to, in the field, as air-balance, air-stat, or flue velocity 

control.

N Fuel Oil - a liquid mixture or compound derived from petroleum that does not emit flammable vapor below a temperature of 

125?F.
O Heat - the warming of a building, apartment, or room by a stove, furnace. or electricity.

P Heating Plant - the furnance, boiler, or the other heating devices used to generate steam, hot water, or hot air, which then is 

circulated through a distribution system. It uses coal, gas, oil, or wood as its source of heat.

Q Limit Control - a thermostatic device installed in the duct system to shut off the supply of heat at a predetermined temperature 

of the circulated air.

R Oil Burner - a device for burning oil in heating appliances such as boilers, furnaces, water heaters, and ranges. A burner of this 

type may be a pressure-atomizing gun type, a horizontal or vertical rotary type, or a mechanical or natural draft vaporizing type.

S Oil Stove - a flue-connected, self-contained, self-supporting oil-burning range or room heater equipped with an integral tank 

not exceeding 10 gallons; it may be designed to be connected to a separate oil supply tank.

T Plenum Chamber - an air compartment to which one or more distributing air ducts are connected.

U Pump, Automatic Oil - a device that automatically pumps oil from the supply tank and delivers it in specific quantities to an oilburning appliance. The pump or device is designed to stop pumping automatically in case of a breakage of the oil supply line.

V Radiant Heat - a method of heating a building by means of electric coils, hot water, or steam pipes installed in the floors, walls, 

or ceilings.

W Register - a grille-covered opening in a floor or wall through which hot or cold air can be introduced into a room. It may or 

may not be arranged to permit closing of the grille.

X Room Heater - a self-contained, free-standing heating appliance intended for installation in the space being heated and not 

intended for duct connection (space heater).

Y Smoke Detector - a device installed in the plenum chamber or in the main supply air duct of an air-conditioning system to shut 

off the blower automatically and close a fire damper in the presence of smoke.

Z Tank - a separate tank connected, directly or by pump, to an oil-burning appliance.

AA Thimble - a term applied to a metal or terra cotta lining for a chimney or furnace pipe.

BB Valve - Main Shut-off Valve-a manually operated valve in an oil line for the purpose of turning on or off the oil supply to the 

burner.

CC Vent System - the gas vent or chimney and vent connector, if used, assembled to form a continuous, unobstructed 

passageway from the gas appliance to the outside atmosphere for the purpose of removing vent gases.

III. Fuels

A Coal

Classification and composition-the four types of coal are: anthracite, bituminous, subbituminous, and lignitic.

Coal is prepared in many sizes and combinations of sizes. The combustible portions of the coal are fixed carbons, volatile 

matter (hydrocarbons), and small amounts of sulfur. In combination with these are non-combustible elements composed of 

moisture and impurities that form ash. The various types differ in heat content. The heat content is determined by analysis 

and is expressed in British Thermal Units (BTU) per pound.

The type and size of coal used are determined by the availability and by the equipment in which it is burned. The type and 
size of coal must be proper for the particular heating unit; that is, the furnace grate and flue size must be designed for the 

particular type of coal. Excessive coal gas can be generated through improper firing as a result of improper fuel or improper 

furnace design, or both.

The owner should be questioned about his procedure for adding coal to his furnace. It should be explained that a period of 

time must be allowed to pass before damping to prevent the release of excessive coal gas. This should also be done before 

damping for the night or other periods when full draft is not required.

Improper coal furnace operation can result in an extremely hazardous and unhealthful occupancy the inspector should be 

able to offer helpful operational procedures. Ventilation of the area surrounding the furnace is very important in order to 

prevent heat buildup and to supply air for combustion.

 

B Fuel Oil

Fuel oils are derived from petroleum, which consists primarily of compounds of hydrogen and carbon (hydrocarbons) and 

smaller amounts of nitrogen and sulfer.

Classification of fuel oils - Domestic fuel oils are controlled by rigid specifications. Six grades of fuel oil are generally used in 

heating systems; the lighter two grades are used primarily for domestic heating.

These grades are:

1. Grade Number 1 -A volatile, distillate oil for use in burners that prepare fuel for burning solely by vaporization (oil-fired 

space heaters). 

2. Grade Number 2 - A moderate-weight, volatile, distillate oil used for burners that prepare oil for burning by a combination of 

vaporization and atomization. This grade of oil is commonly used in domestic heating furnaces. 

3. Grade Number 3 - A low-viscosity, distillate oil used in burners wherein fuel and air are prepared for burning solely by 

atomization. 

4. Grade Number 4 - A medium-viscosity oil used in burners without preheating. (Small industrial or apartment house 

applications.) 

5. Grade Number 5 - A medium-viscosity oil used in burners with preheaters that require an oil of lower viscosity than Grade 

Number 6. (Industrial or apartment house application.) 

6. Grade Number 6 - A high-viscosity oil for use in burners with preheating facilities adequate for handling oil of high viscosity.

(Industrial applications.) 

7. Heat content - Heating values of oil vary from approximately 152,000 BTU per gallon for Number 6 oil to 136,000 BTU per 

gallon for Number 1.

Oil is more widely used today than coal and provides a more automatic source of heat and comfort. It also requires more 

complicated systems and controls.

If the oil supply is used within the basement or cellar area, certain basic regulations must be followed (see Figure 7-1). No more 

than two 275-gallon tanks may be installed above ground in the lowest story of any one building. The tank shall not be closer than 

7 feet horizontally to any boiler, furnace, stove, or exposed flame. Fuel oil lines should be embedded in a concrete or cement floor 

or protected against damage if they run across the floor. Each tank must have a shutoff valve that will stop the flow from each 

tank if a leak develops in the line to or in the burner itself.

The tank or tanks must be vented to the outside, and a gauge showing the quantity of oil in the tank or tanks must be tight and 

operative. Tanks must be off the floor and on a stable base to prevent settlement or movement that may rupture the connections.
A buried outside tank installation is shown in Figure 7-2.

Figure 7-1. Piping Hook-up for Inside Tank Installation

Figure 7-2. Piping Hook-up for Buried Outside Tank

C Gas

Commercial gas fuels are colorless gases. Some have a characteristic pungent odor, while others are odorless and cannot be 

detected by smell. Although gas fuels are easily handled in heating equipment, their presence in air in appreciable quantities 

becomes a serious health hazard. Gases diffuse readily in the air, making explosive mixtures possible. (A proportion of 

combustible gas and air that is ignited burns with such a high velocity that an explosive force is created.) Because of these 

characteristics of gas fuels, precautions must be taken to prevent leaks, and care must be exercised when gas-fired 

equipment is lit.

Classification of gas-Gas is broadly classified as natural or manufactured.

1. Manufactured Gas - This gas as distributed is usually a combination of certain proportions of gases produced by two or more 

processes as obtained from coke, coal, and petroleum. Its BTU value per cubic foot is generally closely regulated, and costs 

are determined on a guaranteed BTU basis, usually 520 to 540 per cubic foot. 

2. Natural Gas - This gas is a mixture of several combustible and inert gases. It is one of the richest gases and is obtained from 

wells ordinarily located in petroleum-producing areas. The heat content may vary from 700 to 1,300 BTU's per cubic foot 

with a generally accepted average figure of 1,000 BTU's per cubic foot. Natural gases are distributed through pipe lines to 

point of utilization and are often mixed with manufactured gas to maintain a guaranteed BTU content. 

3. Liquified Petroleum Gas -Principal products of liquified petroleum gas are butane and propane. Butane and propane are 

derived from natural gas or petroleum refinery gas and are chemically classified as hydrocarbon gases.

Specifically, butane and propane are on the borderline between a liquid and a gaseous state. At ordinary atmospheric pressure 

butane is a gas above 33?F and propane a gas at -42?F. These gases are mixed to produce commercial gas suitable for various 

climatic conditions. Butane and propane are heavier than air. The heat content of butane is 3,274 BTU's per cubic foot while that of 

propane is 2,519.

The gas burner should be equipped with an automatic cutoff in case the flame fails. Shutoff valves should be located within I foot 

of the burner connection and on the output side of the meter.

CAUTION - Liquefied petroleum gas is heavier than air; therefore, the gas will accumulate at the bottom of confined areas. 

If a leak should develop, care should be taken to ventilate the appliance before lighting.

D Electricity

Electricity is gaining popularity in many regions, particularly where costs are competitive with other sources of heat energy. With 

an electric system, the housing inspector should rely mainly on the electrical inspector for proper installation. There are a few 

items, however, to be concerned with to ensure safe use of the equipment. Check to see that the units are accredited testing 

agency approved and installed according to the manufacturer's specifications. Most convector-type units are required to be 

installed at least 2 inches above the floor level, not only to ensure that proper convection currents are established through the 

unit, but also to allow sufficient air insulation from any combustible flooring material. The housing inspector should check for

curtains that extend too close to the unit or loose, long pile rugs that are too close. A distance of 6 inches on the floor and 12 

inches on the walls should separate rug or curtains from the appliance.

Radiant heating plastered into the ceiling or wall is technical in nature and not a part of the housing inspector's competence. He 

should, however, be knowledgeable about the system used. These systems are relatively new. If wires are bared in the plastering 

they should be treated as open and exposed wiring.
IV. Central Heating Units

The boiler should be placed in a separate room whenever possible; in new construction this is usually required. In most housing 

inspections, however, we are dealing with existing conditions; therefore, we must adapt the situation as closely as possible to 

acceptable safety standards. In many old buildings the furnace is located in the center of the cellar or basement, and this location 

does not lend itself for practical conversion to a boiler room. A Boiler Location Consider the physical requirements for a boiler 

room.

1. Ventilation - More circulating air is required for the boiler room than for a habitable room, in order to reduce the heat buildup 

caused by the boiler or furnace as well as to supply oxygen for combustion. 

2. Fire Protection Rating - As specified by various codes (fire code, building code, and insurance underwriters) the fire 

regulations must be strictly adhered to in areas surrounding the boiler or furnace. This minimum dimension from which a 

boiler or furnace is to be spaced from a wall or ceiling is shown in Figure 7-3. 

Many times the enclosure of the furnace or boiler creates a problem of providing adequate air supply and ventilation for the room. 

Where codes and local authority permit, it may be more practical to place the furnace or boiler in an open area. The ceiling above 

the furnace should be fire protected to a distance of 3 feet beyond all furnace or boiler appurtenances and this area should be free 

of all storage material.

The furnace or boiler should be set on a firm foundation of concrete if located in the cellar or basement. If the codes permit 

furnace installations on the first floor, then the building code must be consulted for proper setting and location.

Figure 7-3. Minimum Clearance for Various Types of Central Heating Systems

B Heating Boilers

Boilers may be classified according to several kinds of characteristics. The material may be cast iron or steel. Their construction 

may be section, portable, fire-tube, water-tube; or special. Domestic heating boilers are generally of low-pressure type with a 

maximum working pressure of 15 pounds per square inch for steam and 30 pounds per square inch for hot water.

All boilers have a combustion chamber for burning fuel. Automatic fuel-firing devices help supply the fuel and control the 

combustion. Handfiring is accomplished by the provision of a grate, ash pit, and controllable drafts to admit air under the fuel bed 

and over it through slots in the firing door. A check draft is required at the smoke pipe connection to control chimney draft. The 

gas passes from the combustion chamber to the flue passages (smoke pipe) designed for maximum possible transfer of heat from 

the gas. Provisions must be made for cleaning flue passages.

The term boiler is applied to the single heat source that can supply either steam or hot-water (boiler is often called a heater).

Cast iron boilers are generally classified as:

1. Square or rectangular boilers with vertical sections. 

2. Round, square, or rectangular boilers with horizontal pancake sections.

Cast iron boilers are usually shipped in sections and assembled at the site.

C Steel Boilers

Most steel boilers are assembled units with welded steel construction and are called portable boilers. Larger boilers are installed in 

refractory brick settings built on the site. Above the combustion chamber a group of tubes is suspended, usually horizontally, 

between two headers. If flue gases pass through the tubes and water surrounds them, the boiler is designated as the fire-tube 

type. When water flows through the tubes, it is termed watertube. Fire-tube is the predominant type.
D Heating Furnaces

Heating furnaces are the heat sources used when air is the heat-carrying medium. When air circulates because of the different 

densities of the heated and cooled air, the furnace is a gravity type. A fan may be included for the air circulation; this type is called 

a mechanical warm-air furnace. Furnaces may be of cast iron or steel and burn various types of fuel.

V. Fuel-Burning Procedures and Automatic Firing Equipment

A Coal- Many localities throughout the nation still use coal as a heating fuel.

1. Hand Stoking - In many older furnaces, the coal is stoked or fed into the fire box by hand. 

2. Automatic Stokers - The single-retort, underfeed-type bituminous coal stoker is the most commonly used domestic-type 

steam or hot water boiler (see Figure 7-4). The stoker consists of a coal hopper, a screw for conveying coal from hopper to 

retort, a fan that supplies air for combustion, a transmission for driving coalfeed and fan, and an electric motor for supplying

power. The air for combustion is admitted to the fuel through tuyeres at the top of the retort. The stoker feeds coal to the 

furnace intermittently in accordance with the temperature or pressure demands. 

Figure 7-4. Typical Underfeed Coal Stoker Installation in Small Boiler

B Oil Burners-Oil burners are broadly designated as distillate, domestic, and commercial or industrial. Distillate burners are 

usually found in oil-fired space heaters. Domestic oil burners are usually power driven and are used in domestic heating plants.

Commercial or industrial burners are used in larger central-heating plants for steam or power generation.

1 Domestic Oil Burners - These vaporize and atomize the oil, and deliver a predetermined quantity of oil and air to the combustion 

chambers. Domestic oil burners operate automatically to maintain a desired temperature.

a Gun-type burners - These burners atomize the oil either by oil pressure or by low-pressure air forced through a nozzle.

The oil system pressure atomizing burner (see Figure 7-5) consists of a strainer, pump, pressure-regulating valve, shutoff valve, 

and atomizing nozzle. The air system consists of a power-drive fan and an air tube that surrounds the nozzle and electrode 

assembly. The fan and oil pump are generally connected directly to the motor. Oil pressures normally used are about 100 pounds 

per square inch, but pressures considerably in excess of this are sometimes used.

The form and parts of low-pressure air atomizing burners (see Figure 7-5), are similar to high-pressure atomizing burners except

for addition of a small air pump, and a different way of delivering air and oil to the nozzle or orifice.

b Vertical rotary burners - The atomizing type burner, sometimes known as a radiant or suspended-flame burner, atomizes oil by 

throwing it from the circumference of a rapidly rotating motor-driven cup. The burner is installed so that the driving parts are

protected from the heat of the flame by a hearth of refractory material at about the grate elevation. Oil is fed by pump or gravity, 

while the draft is mechanical or a combination of natural and mechanical.

c Horizontal rotary burners -These were originally designed for commercial and industrial use but are available in sizes suitable for 

domestic use. In this burner, oil is atomized by being thrown in a conical spray from a rapidly rotating cup. Horizontal rotary 

burners employ electric gas or gas-pilot ignition and operate with a wide range of fuels, primarily with Numbers 1 and 2 fuel oil. 

Primary safety controls for burner operation are necessary. An anti-flooding device must be a part of the system so that, if ignition 

in the burner should fail, the oil will not continue to flow. Likewise, a stack control is necessary to shut off the burner if the stack 

temperatures become excessive. A reset button on the older stack control units releases if excessive (predetermined) 

temperatures are exceeded and thus cuts off all power to the burner. This button must be reset before starting can be attempted.

The newer models now use electric eye type control on the burner itself.

Figure 7-5. Cut-Away of Typical High-Pressure Gun Burner
2 Ignition - On the basis of the method employed to ignite fuels, burners are divided into five groups as follows:

a Electric -A high-voltage electric spark is made in the path of an oil and air mixture and this causes ignition. This electric spark 

may be continuous or may be in operation only long enough to ignite the oil. Electric ignition is almost universally used. Electrodes 

are located near the nozzles (see Figure 7-5) but not in the path of the oil Spray.

b Gas pilot -A small gas pilot light that burns continuously is frequently used. Gas pilots usually have expanding gas valves that 

automatically increase flame size when motor circuit starts. After a fixed interval, the flame reverts to normal size.

c Electric gas -An electric spark ignites a gas jet, which in turn ignites the oil air mixture.

d Oil pilot -A small oil flame is used.

e Manual - A burning wick or torch is placed in the combustion space through peepholes and thus ignites the charge. Operator 

should stand to one side of the fire door to guard against injury from chance explosion.

VI. Refractory

The refractory lining or material should be an insulating fireproof brick-like substance. Never use ordinary firebrick. The insulating 

brick should be set on end so as to build a 2 inch-thick wall in the pot. Size and shape of the refractory pot vary from furnace to 

furnace (see Figure 7-6 for various shapes). The shape can be either round or square, whichever is more convenient to build. It is 

important to use a special cement having properties similar to that of the insulating refractory-type brick.

Figure 7-6. Refactory Pot Details

VII. Heating Systems

A Steam Heating Systems -Steam heating systems are classified according to the pipe arrangement, accessories used, method 

of returning the condensate to the boiler, method of expelling air from the system, or the type of control employed. The successful 

operation of a steam heating system consists of generating steam in sufficient quantity to equalize building heat loss at maximum 

efficiency, expelling entrapped air, and returning all condensate to the boiler rapidly. Steam cannot enter a space filled with air or 

water at pressure equal to the steam pressure. It is important, therefore, to eliminate air and to remove water from the 

distribution system. All hot pipe lines exposed to contact by residents must be properly insulated or guarded.

Steam heating systems are classified according to the method of returning the condensate to the boiler.

1 Gravity One-pipe Air-vent System - The gravity one-pipe air-vent system is one of the earliest types used. The condensate is

returned to the boiler by gravity. This system is generally found in one-building-type heating systems. The steam is supplied by

the boiler and carried through a single system or pipe to radiators as shown in Figure 7-7. Return of the condensate is dependent 

on hydrostatic head. Therefore, the end of the steam main, where it attaches to the boiler, must be full of water (termed a wet 

return) for a distance above the boiler line to create a pressure drop balance between the boiler and the steam main.

Radiators are equipped with an inlet valve and with an air valve (see Figure 7-8). The air valve permits venting of air from the

radiator and its displacement by steam. Condensate is drained from the radiator through the same pipe that supplies steam.

Figure 7-7 Typical Gravity One-Pipe Steam Heating System & Figure 7-8. Safety Air Valve

2 Two-pipe Steam Vapor System with Return Trap -The two-pipe vapor system with boiler return trap and air eliminator is an 

improvement of the one-pipe system. The return connection of the radiator has a thermostatic trap that permits flow of 

condensate and air only from the radiator and prevents steam from leaving the radiator. Since the return main is at atmospheric 

pressure or less, a boiler return trap is installed to equalize condensate return pressure with boiler pressure. B Hot Water Heating 

Systems - All hot water heating systems are similar in design and operating principle.
1 One-pipe Gravity System - The one-pipe gravity hot water heating system is the most elementary of the gravity systems and 

is shown in Figure 7-9. Water is heated at the lowest point in the system. It rises through a single main because of a difference in 

density between hot and cold water. The supply rise or radiator branch takes off from the top of the main to supply water to the

radiators. After the water gives up heat in the radiator it goes back to the same main through return piping from the radiator. This 

cooler return water mixes with water in the supply main and causes the water to cool a little. As a result, the next radiator on the 

system has a lower emission rate and must be larger.

Note in Figure 7-9 that the high points of the hot water system are vented and the low points are drained. In this case, the 

radiators are the high points and the heater is the low point.

2 One-pipe Forced-feed System -If a pump or circulator is introduced in the main near the heater of the one-pipe system, we 

have a forced system that can be used for much larger applications than the gravity type. This system can operate at higher water 

temperatures than the gravity system. The faster moving higher temperature water makes a more responsive system with a 

smaller temperature drop through each radiator. Higher operating temperatures and lower temperature drops permit the use of 

smaller radiators for the same heating load.

Figure 7-9. One Pipe Gravity Hot Water Heating System

3 Two-Pipe Gravity Systems -One-pipe gravity systems may become a two-pipe system if the return radiator branch connects to 

a second main that returns water to the heater (see Figure 7-10). Water temperature is practically the same in all the radiators.

Figure 7-10. Two-Pipe Gravity Hot-Water System

4 Two-pipe Forced-circulation System - This system is similiar to a one-pipe forced-circulation system except that the same 

piping arrangement is found in the two-pipe gravity flow system.

5 Expansion Tanks -When water is heated it tends to expand. Therefore, in a hot water system an expansion tank is necessary. 

The expansion tank, either of open or closed type, must be of sufficient size to permit a change in water volume within the heating 

sv m. If the expansion tank is of the open type it must be placed at least 3 feet above the highest point of the system. It will

require a vent and an overflow. The open tank is usually in an attic, where it needs protection from freezing.

The enclosed expansion tank is found in modern installations. An air cushion in the tank compresses and expands according to the

change of volume and pressure in the system. Closed tanks are usually at the low point in the system and close to the heater. 

They can, however, be placed at almost any location within the heating system. C Hot Air Heating Systems

1 Gravity-Warm-Air Heating Systems - These operate because of the difference in specific gravity of warm air and cold air. Warm

air is lighter than cold air and rises if cold air is available to replace it (see Figure 7-11).

Figure 7-11. Hot Air Furnance

1. Approximately 12 pounds of air is required for complete combustion of 1 pound of hard coal.

2. Approximately 5 pounds of hard coal is consumed per hour for each square foot of grate area 3. Approximately 12 inches 

of fire bed will heat most efficiently.

4. Anthracite coal burns more slowly than soft coal, is cleaner to handle-hence more widely used.

5. Large-size coal does not compact-hence the air spaces are too great and allows gases to escape into the flue unburned. 

Small size coal compacts too much and inhibits airflow through the coal to allow for good combustion. Mixing of coal size is 

recommended, i.e., stove and chestnut.

6. Fires burn best when the weather is clear and cold, because of reduced atmospheric pressure on the air in the flue-hence 

greater draft velocity. During periods of heavy atmosphere or rainy weather the temperature of flue gases must exceed 
normal temperatures to overcome the heavier atmospheric weight.

7. During extreme cold weather, coal should be added to a fire once in approximately 8 hours: moderate weather-12 hours.

a Operation - Satisfactory operation of a gravity-warm-air heating system depends on three factors. They are: ( 1 ) size of warm

air and cold ducts, (2) heat loss of the building, (3) heat available from the furnace.

b Heat distribution - The most common source of trouble in these systems is insufficient pipe area usually in the return or cold air 

duct. The total cross-section area of the cold duct or ducts must be at least equal to the total cross-section area of all warm ducts.

c Pipeless furnaces- The pipeless hot-air furnace is the simplest type of hot-air furnace and is suitable for small homes where all 

rooms can be grouped about a single large register (see Figure 7-3). Other pipeless gravity furnaces are often installed at floor 

level. These are really oversized jacketed space heaters. The most common difficulty experienced with this type of furnace is 

supplying a return air opening of sufficient size on the floor.

2 Forced - Warm-Air Heating Systems - The mechanical warm-air furnace is the most modem type of warm-air equipment (see 

Figure 7-12). It is the safest type because it operates at low temperatures. The principle of a forced warm air heating system is 

very similar to that of the gravity system, except that a fan or blower is added to increase air movement. Because of the 

assistance of the fan or blower, the pitch of the ducts or leaders can be disregarded and it is therefore practical to deliver heated 

air in the most convenient places.

a Operation -In a forced-air system, operation of the fan or blower must be controlled by air temperature in a bonnet or by a 

blower control furnacestat. The blower control starts the fan or blower when the temperature reaches a certain point and turns the 

fan or blower off when the temperature drops to a predetermined point.

b Heat distribution - Dampers in the various warm-air ducts control distribution of warm air either at the branch takeoff or at the 

warm-air outlet.

Humidifiers are often mounted in the supply bonnet in order to regulate the humidity within the residence.

D Space Heaters - Space unit heaters are the least desirable from the viewpoint of fire safety and housing inspection. All space

unit heaters must be vented to the flue.

Figure 7-12. Cross Sectional View of Building Showing Forced-Warm-Air Heating System

l Coal-Fired Space Heaters (Cannon stove) - This is illustrated in Figure 7-13 and is made entirely of cast iron. In operation, coal 

on the grates receives primary air for combustion through the grates from the ash-door draft intake. Combustible gases driven 

from the coal by heat burn in the barrel of the stove, where they received additional or secondary air through the feed door. Side 

and top of the stove absorb the heat of combustion and radiate it to the surrounding space.

2 Oil-Fired Space Heaters - Oil-fired space heaters have atmospheric vaporizing-type burners. The burners require a light grade 

of fuel oil that vaporizes easily and is comparatively low in temperature. In addition, the oil must be such that it leaves only a 

small amount of carbon residue and ash within the heater.

Oil-fired space heaters are basically of two types:

a Perforated-sleeve burner -The perforated sleeve burner (see Figure 7-14) consists essentially of a metal base formed of two or 

more angular fuel-vaporizing bowl burners (see Figure 7-15) and is widely used in space heaters and some water heaters.

Figure 7-13. Cannon Stove

Figure 7-14. Perforated-Sleeve Burner.
Figure 7-15. Natural-Draft Pot Burner

The burner consists essentially of a bowl, 8 to 13 inches in diameter, with perforations in the side that admit air for combustion. 

The upper part of the bowl has a flame ring or collar. When several space heaters are installed in a building, an oil supply from an 

outside tank to all heaters is often desirable. Figure 7-16 shows the condition of a burner flame with different rates of fuel flow and 

indicates the ideal flame height .

Figure 7-16. Condition of Burner Flame with Different Rates of Fuel Flow

3 Gas-Fired Space Heaters - There are three types of gas-fired space heaters: natural, manufactured, and liquefied petroleum 

gas. Space heaters using natural, manufactured, or liquefied petroleum gases have a similar construction. All gas-fired space 

heaters must be vented to prevent a dangerous buildup of poisonous gases.

Each unit console consists of an enamel steel cabinet with top and bottom circulating grilles or openings, gas burners, heating 

element, gas pilot, and gas valve (see Figure 7-17). The heating element or combustion chamber is usually cast iron.

Figure 7-17. Typical Gas-Fired Space Heater

CAUTION: All gas-fired space heaters and their connections must be of the type approved by the American Gas Association 

(AGA). They must be installed in accordance with the recommendations of that organization or the local code.

a Venting - Use of proper venting materials and correct installation of venting for gas-fired space heaters is necessary to minimize 

harmful effects of condensation and to ensure that combustion products are carried off. (Approximately 12 gallons of water are 

produced in the burning of 1,000 cubic feet of natural gas. The inner surface of the vent must therefore be heated above the dew

point of the combustion products to prevent water from forming in the flue.) A horizontal vent must be given an upward pitch of at 

least 1 inch per foot of horizontal distance.

When the smoke pipe extends through floors or walls the metal pipe must be insulated from the floor or wall system by an air 

space (see Figure 7-18). Avoid sharp bends. A 90? vent elbow has a resistance to flow equivalent to a straight section of pipe 

having a length of 10 times the elbow diameter. Be sure vent is of a rigid construction and resistant to corrosion by flue gas 

products. Several types of venting material are available such as B-vent and several other ceramic -type materials. A chimney 

lined with fire-brick type of terra cotta must be relined with an acceptable vent material if it is to be used for venting gas-fired 

appliances.

Use the same size vent pipe throughout its length. Never make a vent smaller than heater outlet except when two or more vents 

converge from separate heaters. To determine the size of vents beyond the point of convergence, add one-half the area of each 

vent to the area of the largest heater's vent.

Figure 7-18. Wall and Ceiling Clearance Reduction

Install vents with male ends of inner liner down to ensure condensate is kept within pipes on a cold start. The vertical length of 

each vent or stack should be at least 2 feet greater than the length between horizontal connection and stack.

Run vent at least 3 feet above any projection of the building within 20 feet to place it above a possible pressure zone due to wind 

currents (see Figure 7-19). End it with a weather cap designed to prevent en entrance of rain and snow.

Gas-fired space heaters as well as gas furnaces and hot water heaters must be equipped with a backdraft diverter (see Figure 7-

20) designed to protect heaters against downdrafts and excessive updrafts. Use only draft diverters of the type approved by the 

AGA.

Figure 7-19. Draft Relation to Height of Chimney.

Figure 7-20. Location and Operation of Typical Backdraft Diverter
The combustion chamber or firebox must be insulated from the floor, usually with an airspace of 15 to 18 inches, or the firebox is 

sometimes insulated within the unit and thus allows for lesser clearance for combustibles.

Where coal space heaters are located, a floor protection should be provided. This would be a metal-covered asbestos board or a 

similar durable insulation material. One reason for the floor protection would be to allow cooling off of hot coals and ashes if they 

drop out while ashes are being removed from the ash chamber. Walls and ceilings of a non-combustible construction exposed to 

furnace radiation should be installed, and the following clearances are recommended:

Space heaters-A top or ceiling clearance of 36 inches, a wall clearance of 18 inches, and a smoke pipe clearance of 18 inches, (see 

Figure 7-18).

VIII. Domestic Hot Water Jack Stoves (Coal Stoves)

Domestic hot water jack stoves (coal stoves) equipped with water jackets to supply hot water for domestic use are to be treated as 

coal-fired furnaces or boilers previously discussed. Note that flue connections should not exceed two to the same flue unless the 

draft and size are sufficient to accommodate both exhausting requirements. One flue with one smoke pipe is the rule; however, 

housing inspectors may find a jack stove and main furnace connected to the same flue. Where these conditions are encountered 

and no complaint about malfunctioning of this system is found, it can be assumed that the system is operating satisfactorily. 

Where more than two units, other than gas, are attached to a single flue, the building agency should be notified, since this can be 

considered an improper installation. Gas, oil, and electric hot water heating units for domestic hot water should be treated the

same as previously discussed for central heating units.

IX. Hazardous Installations

A Generalities - The housing inspector should be on the alert for unvented open burning flame heaters, such as manually 

operated gas logs. Coil-type wall-mounted hot-water heaters that do not have safety relief valves are not permitted. Kerosene 

(portable) units for cooking or heating should be prohibited. Generally, open-flame portable units are not allowed under; fire safety 

regulations.

In oil heating units, other than integral tank units, the oil filling and vent must be located on the exterior of the building. Filling of 

oil within buildings is prohibited.

Electric wiring to heating units must be installed as indicated in the electrical section. Cutoff switches should be close to the entry 

but outside of the boiler room. The inspector should be able to appraise the heating installation and determine its adequacy. Any 

installation that indicates haphazard location, workmanship, or operation, whether it be building, zoning, plumbing, electrical, or 

housing, will dictate further inspection.

B Chimneys (see Figure 7-21 and 7-22) - Chimneys, as all inspectors know, are an integral part of the building. The chimney 

is a point of building safety and should be understood by the housing inspector. The chimney, if of masonry, must be tight and 

sound; flues should be terra cotta lined, and where no linings are installed, the brick should be tight to permit proper draft and 

elimination of combustion gases.

Chimneys that act as. flues for gas-fired equipment must be lined with either B-vent or terra cotta.

To the inspector, on exterior inspection, "banana peel" on the portion of the chimney above the roof will indicate trouble and a

need for rebuilding. Exterior deterioration of the chimney will, if let go too long, gradually permit erosion from within the flues and 

eventually block the flue opening.

Rusted flashing at the roof level will also contribute to the chimney's deterioration. Effervescence on the inside wall of the chimney 

below the roof and on the outside of the chimney, if exposed, will show salt accumulations - a tell-tale sign of water penetration 

and flue gas escape and a sign of chimney deterioration. In the spring and fall, during rain seasons, if terra cotta chimneys leak, 

the joint will be indicated by dark areas permitting actual counting of the number of flues inside the masonry chimney. When this 

condition occurs, it usually requires 2 or 3 months to dry out. Upon drying out, the mortar joints are discolored (brown), and so 
after a few years of this type of deterioration the joints can be distinguished wet or dry. The above listed conditions usually 

develop during coal operation and become more pronounced usually 2 to 5 years after conversion to oil or gas.

An unlined chimney can be checked for deterioration below the roof line by checking the residue deposited at the base of the 

chimney, usually accessible through a cleanout (door or plug) or breaching. Red granular or fine powder showing through coal soot 

or oil soot will generally indicate, if in quantity (a handful), that deterioration is excessive and repairs are needed.

Gas units attached to unlined chimneys will be devoid of soot, but will usually show similar tell-tale brick powder and deterioration 

as previously mentioned. Manufactured gas has a greater tendency to dehydrate and decompose brick in chimney flues than 

natural gas. For gas installations in older homes, utility companies usually specify chimney requirements before installation, and so 

older chimneys may require the installation of terra cotta liners, lead-lined copper liners, or transite pipe. Oil burner operation 

using a low air ratio and high oil consumption is usually indicated by black carbon deposits around the top of the chimney. 

Prolonged operation in this burner setting results in long carbon water deposits down the chimney for 4 to 6 feet or more and 

should indicate to the inspector a possibility of poor burner maintenance. This will accent his need to be more thorough on the 

ensuing inspection. This type of condition can result from other related causes, such as improper chimney height or exterior 

obstructions such as trees or buildings that will cause downdrafts or insufficient draft or contribute to a faulty heating operation.

Rust spots and soot-mold usually occur on galvanized smoke pipe deterioration.

Figure 7-21. Chimney Plan

C Fireplace - Careful attention should be given to the construction of the fireplace. Improperly built fireplaces are a serious 

safety and fire hazard (see Figure 7-22). The most common causes of fireplace fires are thin walls, combustible materials such as 

studding or trim against sides and back of the fireplace, wood mantels, and unsafe hearths.

Fireplace walls should be not less than 8 inches thick, and if built of stone or hollow masonry units, not less than 12 inches thick. 

The faces of all walls exposed to fire should be lined with firebrick or other suitable fire-resistive material. When the lining consists 

of 4 inches of firebrick, such lining thickness may be included in the required minimum thickness of the wall.

The fireplace hearth should be constructed of brick, stone, tile, or similar incombustible material and should be supported on a

fireproof slab or on a brick arch. The hearth should extend at least 20 inches beyond the chimney breast and not less than 12 

inches beyond each side of the fireplace opening along the chimney breast. The combined thickness of the hearth and its 

supporting construction should be not less than 6 inches at any point.

It is important that all wooden beams, joists, and studs are set off from the fireplace and chimney so that there is not less. than 2 

inches of clearance between the wood members and the sidewalls of the fireplace or chimney and not less than 4 inches of 

clearance between wood members and the back wall of the fireplace.

The housing inspector is a very important person in maintaining sound, safe, and healthful community growth. This should be a 

challenge to every inspector to provide himself with the necessary tools for better and more efficient housing inspection. He must 

develop the extra senses so necessary in spotting and correcting faults. He must know when to refer and to whom the referral is to 

be made; he must be continually seeking knowledge, which may be found by consulting with technicians, tradesmen, and 

professionals. No finer satisfaction can be realized than to know and feel that the security, safety, and comfort of each and every 

family within your community has a better and more healthful life because of that extra bit of knowledge you have imparted. "An 

inspector who stops learning today is uneducated tomorrow."

Table of Contents | Acknowledgements | Foreword | Chapter1 | Chapter 2

Chapter 3 | Chapter 4 | Chapter 5 | Chapter 6 | Chapter 7

Chapter 8 | Chapter 9 | Chapter 10 | Chapter 11

 
 

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