Table of Contents
Title Page
Copyright Page
About the Author
Chapter 1 - Radiant Heating
Types of Radiant Panel Heating Systems
Hydronic Radiant Floor Heating
Electric Radiant Floor Heating
Cooling for Hydronic Radiant Floor Systems
Chapter 2 - Radiators, Convectors, and Unit Heaters
Steam and Hot-Water Baseboard Heaters
Electric Baseboard Heaters
Kickspace Heaters
Floor and Window Recessed Heaters
Unit Heaters
Chapter 3 - Fireplaces, Stoves, and Chimneys
Modified Fireplaces
Freestanding Fireplaces
Rumford Fireplace
Chimney Draft
Chimney Construction Details
Chimney Flues and Chimney Liners
Smoke Pipe
Cleanout Trap
Chimney Downdraft
Prefabricated Metal Chimneys
Troubleshooting Fireplaces and Chimneys
Stoves, Ranges, and Heaters
Installation Instructions
Operating Instructions
Chapter 4 - Water Heaters
Types of Water Heaters
Water Heater Construction Details
Gas-Fired Water Heaters
Storage Capacity
Automatic Controls on Gas-Fired Water Heaters
Combination Gas Valve
Installation and Operation of Gas-Fired Water Heaters
Hot-Water Circulating Methods
Building and Safety Code Requirements
Lighting and Operating Instructions
Installation and Maintenance Checklist
Troubleshooting Gas-Fired Water Heaters
Oil-Fired Water Heaters
Electric Water Heaters
Troubleshooting Electric Water Heaters
Manual Water Heaters
Solar Water Heaters
Chapter 5 - Heating Swimming Pools
Classifying Pool Heaters
Gas-Fired Pool Heaters
Oil-Fired Pool Heaters
Electric Pool Heaters
Heat-Exchanger Pool Heaters
Solar Pool Heaters
Heat Pump Pool Heaters
Sizing Pool Heaters
Sizing Indoor Pool Heaters
Installing Pool Heaters
Pool Heater Repair and Maintenance
Troubleshooting Pool Heaters and Equipment
Chapter 6 - Ventilation Principles
The Motive Force
Inductive Action of the Wind
Induced Draft
Combined Force of Wind Effect and Thermal Effect
Mechanical Ventilation
Air Ventilation Requirements
Roof Ventilators
Types of Roof Ventilators
Components of a Roof Ventilator
Motive Force to Cause Air Circulation
Capacity of Ventilators
Design and Placement of Inlet Air Openings
Fresh Air Requirements
Ventilator Bases
Angle Rings
Stiffener Angles
Prefabricated Roof Curbs
Ventilator Dampers
Method of Calculating Number and Size of Ventilators Required
Ventilator Calculation Examples
Air Leakage
Garage Ventilation
Ventilation of Kitchens
General Ventilation Rules
Chapter 7 - Ventilation and Exhaust Fans
Codes and Standards
Types of Fans
Furnace Blowers
Basic Fan Laws
Series and Parallel Fan Operation
Fan Performance Curves
General Ventilation
Determining Air Intake
Screen Efficiency
Static Pressure
Local Ventilation
Exhaust-Hood Design Recommendations
Fan Motors
Troubleshooting Fans
Fan Selection
Fan Installation
Fan Installation Checklist
Air Volume Control
Noise Control
Fan Applications
Attic Ventilating Fans
Exhaust Fans
Whole-House Ventilation
Chapter 8 - Air-Conditioning
Properties of Air
Compression and Cooling
Measuring the Physical Properties of Air
Cleaning and Filtering the Air
Standards of Comfort
The Comfort Chart
Cooling Load Estimate Form
Indoor-Outdoor Design Conditions
Ventilation Requirements
Cooling a Structure
Calculating Infiltration and Ventilation Heat Gain
Rule-of-Thumb Methods for Sizing Air Conditioners
HVAC Contractor’s Cooling Load Estimate
Using the ACCA Design Manuals for Sizing Air-Conditioning Systems
Central Air-Conditioning
Room Air Conditioners
Chapter 9 - Air-Conditioning Equipment
Mechanical Refrigeration Equipment
Troubleshooting Compressors
Compressor Replacement
Electric Motors
Troubleshooting Electrical Motors
Gas Engines
Electrical Components
Troubleshooting Electrical Components
Liquid Refrigerant Control Devices
Automatic Expansion Valves
Thermostatic Expansion Valves
Float Valves
Capillary Tubes
Refrigerant Piping
Filters and Dryers
Pressure-Limiting Controls
Water-Regulating Valves
Automatic Controls
System Troubleshooting
General Servicing and Maintenance
Chapter 10 - Heat Pumps
Heat Pump Operating Principles
Types of Heat Pumps
Other Types of Heat Pumps
Heat Pump Performance and Efficiency Ratings
Heat Pump System Components
Sizing Heat Pumps
Heat Pump Installation Recommendations
Heat Pump Operating Instructions
Heat Pump Service and Maintenance
Troubleshooting Heat Pumps
Troubleshooting Heat Pump Compressors
Chapter 11 - Humidifiers and Dehumidifiers
Automatic Controls
Installation Instructions
Service and Maintenance Suggestions
Troubleshooting Humidifiers
Absorption Dehumidifiers
Spray Dehumidifiers
Refrigeration Dehumidifiers
Troubleshooting Dehumidifiers
Chapter 12 - Air Cleaners and Filters
Electronic Air Cleaners
Automatic Controls
Clogged-Filter Indicator
Performance Lights
Sail Switch
In-Place Water-Wash Controls
Cabinet-Model Control Panels
Installation Instructions
Electrical Wiring
Maintenance Instructions
Replacing Tungsten Ionizing Wires
Troubleshooting Electronic Air Cleaners
Air Washers
Air Filters
Dry Air Filters
Viscous Air Filters
Filter Installation and Maintenance
Appendix A - Professional and Trade Associations
Appendix B - Manufacturers
Appendix C - HVAC/R Education,Training, Certification, and Licensing
Appendix D - Data Tables
Appendix E - Psychrometric Charts


For Laura, my friend, my daughter.

The purpose of this series is to provide the layman with an introduction to the fundamentals of installing, servicing, troubleshooting, and repairing the various types of equipment used in residential and light-commercial heating, ventilating, and air conditioning (HVAC) systems. Consequently, it was written not only for the HVAC technician and others with the required experience and skills to do this type of work but also for the homeowner interested in maintaining an efficient and trouble-free HVAC system. A special effort was made to remain consistent with the terminology, definitions, and practices of the various professional and trade associations involved in the heating, ventilating, and air conditioning fields.
Volume 1 begins with a description of the principles of thermal dynamics and ventilation, and proceeds from there to a general description of the various heating systems used in residences and light-commercial structures. Volume 2 contains descriptions of the working principles of various types of equipment and other components used in these systems. Following a similar format, Volume 3 includes detailed instructions for installing, servicing, and repairing these different types of equipment and components.
The author wishes to acknowledge the cooperation of the many organizations and manufacturers for their assistance in supplying valuable data in the preparation of this series. Every effort was made to give appropriate credit and courtesy lines for materials and illustrations used in each volume.
Special thanks is due to Greg Gyorda and Paul Blanchard (Watts Industries, Inc.), Christi Drum (Lennox Industries, Inc.), Dave Cheswald and Keith Nelson (Yukon/Eagle), Bob Rathke (ITT Bell & Gossett), John Spuller (ITT Hoffman Specialty), Matt Kleszezynski (Hydrotherm), and Stephanie DePugh (Thermo Pride).
Last, but certainly not least, I would like to thank Katie Feltman, Kathryn Malm, Carol Long, Ken Brown, and Vincent Kunkemueller, my editors at John Wiley & Sons, whose constant support and encouragement made this project possible.
James E. Brumbaugh

About the Author
James E. Brumbaugh is a technical writer with many years of experience working in the HVAC and building construction industries. He is the author of the Welders Guide, The Complete Roofing Guide, and The Complete Siding Guide.

Chapter 1
Radiant Heating
Heat is lost from the human body through radiation, convection, and evaporation. Radiation heat loss represents the transfer of energy by means of electromagnetic waves. The convection loss is the heat carried away by the passage of air over the skin and clothing. The evaporation loss is the heat used up in converting moisture on the surface of the skin into vapor.
Heat transfer, whether by convection or radiation, follows the same physical laws in the radiant heating system as in any other; that is, heat flows from the warmer to the cooler exposure at a rate directly proportional to the existing temperature difference.
The natural tendency of warmed air to rise makes it apparent that this induced air current movement is greater at the cooler floor and exterior walls of the average heated enclosure than at its ceiling. It is through absorption by these air currents that the radiant panel releases the convection component of its heat transfer into the room air.
The average body heat loss is approximately 400 Btu per hour; total radiation and convection account for approximately 300 to 320 Btu of it. Because this is obviously the major portion, the problem of providing comfort is principally concerned with establishing the proper balance between radiation and convection losses.
It is important to understand that bodily comfort is obtained in radiant heating by maintaining a proper balance between radiation and convection. Thus, if the air becomes cooler and accordingly the amount of heat given off from the body by convection increases, then the body can still adjust itself to a sense of comfort if the heat given off from the body by radiation is decreased. The amount given off from the body by radiation can be decreased by raising the temperature of the surrounding surfaces, such as the walls, floor, and ceiling. For comfort, the body demands that if the amount of heat given off by convection increases, the heat given off by radiation must decrease, and vice versa.
The principles involved in radiant heating exist in such commonplace sources of heat as the open fireplace, outdoor campfires, electric spot heaters, and similar devices. In each of these examples, no attempt is made to heat the air or enclosing surfaces surrounding the individual. In fact, the temperature of the air and surrounding surfaces may be very low, but the radiant heat from the fireplace or campfire will still produce a sensation of comfort (or even discomfort from excess heat) to those persons within range. This situation can occur even though a conventional thermometer may indicate a temperature well below freezing. Radiant heat rays do not perceptibly heat the atmosphere through which they pass. They move from warm to colder surfaces where a portion of their heat is absorbed.
This chapter is primarily concerned with a description of radiant panel heating, which can be defined as a form of radiant heating in which large surfaces are used to radiate heat at relatively low temperatures. The principal emphasis will be on hydronic and electric radiant floor heating.

Types of Radiant Panel Heating Systems

Radiant panel heating systems use water-filled tubing or electric heating mats or rolls installed in the floors, walls, and ceilings to distribute the heat. Radiant floor heating is by far the most popular installation method in residential and light-commercial construction.
The word panel is used to indicate a complete system of tubing loops in a single room or space in a structure. It may also be used to indicate a premanufactured radiant floor heating panel.

Floor Panel Systems

Floor panels are usually easier to install than either ceiling or wall panels. Using floor panels is the most effective method of eliminating cold floors in slab construction. Another advantage of heating with floor panels is that much of the radiated heat is delivered to the lower portions of the walls. The principal disadvantage of using floor panels is that furniture and other objects block portions of the heat emission.
Floor panels are recommended for living or working areas constructed directly on the ground, particularly one-story structures. Partial ceiling or wall treatment may be used as a supplement wherever large glass or door exposures are encountered. A typical floor installation is shown in Figure 1-1.

Ceiling Panel Systems

The advantage of a ceiling panel is that its heat emissions are not affected by drapes or furniture. As a result, the entire ceiling area can be used as a heating panel. Ceiling panels are recommended for rooms or space with 7-foot ceilings or higher. A ceiling panel should never be installed in a room with a low ceiling (under 7 feet) because it may produce an undesirable heating effect on the head.
Figure 1-1 Diagram of a typical radiant floor heating installation.
In multiple-story construction, the use of ceiling panels appears to be more desirable from both the standpoint of physical comfort and overall economy. The designed utilization of the upward heat transmission from ceiling panels to the floor of the area immediately above will generally produce moderately tempered floors. Supplementing this with automatically controlled ceiling panels will result in a very efficient radiant heating system. Except directly below roofs or other unheated areas, this design eliminates the need for the intermediate floor insulation sometimes used to restrict the heat transfer from a ceiling panel exclusively to the area immediately below. It must be remembered, however, that when intermediate floor insulations are omitted, the space above a heated ceiling will not be entirely independent with respect to temperature control but will necessarily be influenced by the conditions in the space below. A typical ceiling installation is shown in Figure 1-2.
Figure 1-2 Diagram of a typical radiant ceiling heating panel.
Apartment buildings and many office and commercial structures should find the ceiling panel method of radiant heating most desirable. In offices and stores, the highly variable and changeable furnishings, fixtures, and equipment favor the construction of ceiling panels, to say nothing of the advantage of being able to make as many partition alterations as desired without affecting the efficiency of the heating system.

Wall Panel Systems

Walls are not often used for radiant heating because large sections of the wall area are often interrupted by windows and doors. Furthermore, the heat radiation from heating coils placed in the lower sections of a wall will probably be blocked by furniture. As a result, a radiant wall installation is generally used to supplement ceiling or floor systems, not as a sole source of heat.
Wall heating coils are commonly used as supplementary heating in bathrooms and in rooms in which there are a number of large picture windows. In the latter case, the heating coils are installed in the walls opposite the windows. Wall heating coils will probably not be necessary if the room has good southern exposure. A typical wall installation is shown in Figure 1-3.
Figure 1-3 Typical wall installation. Panel is installed on wall as high as possible.

Hydronic Radiant Floor Heating

Hydronic radiant floor systems heat water in a boiler, heat pump, or water heater and force it through tubing arranged in a pattern of loops located beneath the floor surface. These systems can be classified as being either wet installations or dry installations depending on how the tubing is installed.
In wet installations, the tubing is commonly embedded in a concrete foundation slab or attached to a subfloor and covered with a lightweight concrete slab. Dry installations are so called because the tubing is not embedded in concrete.

System Components

The principal components of a typical hydronic radiant floor heating system can be divided into the following categories:
1. Boilers, water heaters, and heat pumps
2. Tubing and fittings
3. Valves and related controls
4. Circulator
5. Expansion tank
6. Air separator
7. Heat exchanger
8. Thermostat

Boilers, Water Heaters, and Heat Pumps

The boilers used in hot-water radiant heating systems are the same types of heating appliances as those used in hydronic heating systems. Information about the installation, maintenance, service, and repair of hydronic boilers is contained in Chapter 15 of Volume 1.
Gas-fired boilers are the most widely used heat source in hydronic radiant heating systems. Oil-fired boilers are second in popularity and are used most commonly in the northern United States and Canada. Coal-fired boilers are still found in some hydronic radiant heating systems, but their use has steadily declined over the years.
Hydronic radiant floor heating systems operate in an 85-140ºF (29-60ºC) temperature range.This is much lower than the 130- 160ºF (54-71ºC) temperature operating range required in other hydronic systems. As a result, the boilers used in floor systems operate at lower boiler temperatures, which results in a much longer service life for the appliance.
The electric boilers used in hydronic radiant floor systems are competitive with other fuels in those areas where electricity costs are low. Their principal advantage is that they are compact appliances that can be installed where space is limited.
Radiant floor systems can also be heated with a geothermal heat pump. In climates where the heating and cooling loads are equal or almost equal in size, a geothermal heat pump will be very cost effective.
Most standard water heaters produce a maximum of 40,000 to 50,000 Btu/h. This is sufficient Btu input to heat a small house or to separately heat a room addition, but it cannot provide the heat required for medium to large houses. As a result, some HVAC manufacturers have developed high-Btu-output dedicated water heaters for radiant heating systems. These water heaters are designed specifically as single heat sources for both the domestic hot water and the space-heating requirements. As is the case with boilers used in hydronic radiant heating systems, they operate in conjunction with a circulating pump and an expansion tank. See Chapter 4 (“Water Heaters”) for additional information about combination water heaters.

Tubing and Fittings

The tubing in a radiant heating system is divided into the supply and return lines. The supply line extends from the discharge opening of a boiler to the manifold. It carries the heated fluid to the loops (circuits) in the floors, walls, or ceilings. A return line extends from the return side of a manifold to the boiler. It carries the water from the heating panels back to the boiler where it is reheated.
Hydronic radiant floor heating systems use copper, plastic (PEX or polybutylene tubing), or synthetic-rubber tubing to form the loops. Because of space limitations, only the two most commonly used types are described in this chapter: copper tubing and PEX (plastic) tubing. Information about the other types of tubing used in hydronic heating systems can be found in Chapter 8 (“Pipes, Pipe Fittings, and Piping Details”) of Volume 2.
Loops or Circuits
The words loop and circuit are synonyms for the length of tubing within a zone. Sometimes both are used in the same technical publication. At other times, one or the other is used exclusively. Many loops or circuits of the same length will form a zone. Circuits also refer to the electrical circuit required to operate the heating system.

Copper Tubing

In most modern radiant floor heating systems, the water is circulated through copper or cross-linked polyethylene (PEX) tubing (see Figure 1-4). The metal coils used in hydronic radiant heating systems commonly are made of copper tubing (both the hard and soft varieties). Steel and wrought-iron pipe also have been used in hydronic floor heating systems, but it is rare to find them in modern residential radiant floor heating systems.
Figure 1-4 Copper tubing.
The soft tempered Type L copper tubing is recommended for hydronic radiant heating panels. Because of the relative ease with which soft copper tubes can be bent and shaped, they are especially well adapted for making connections around furnaces, boilers, oilburning equipment, and other obstructions. This high workability characteristic of copper tubing also results in reduced installation time and lower installation costs. Copper tubing is produced in diameters ranging from 1/8 inch to 10 inches and in a variety of different wall thicknesses. Both copper and brass fittings are available. Hydronic heating systems use small tube sizes joined by soldering.
The size of the pipes or tubing used in these systems depends on the flow rate of the water and the friction loss in the tubing. The flow rate of the water is measured in gallons per minute (gpm), and constant friction loss is expressed in thousandths of an inch for each foot of pipe length. For a description of the various types of tubing used in hydronic heating systems, see the appropriate sections of Chapter 8 (“Pipes, Pipe Fittings, and Piping Details”) in Volume 2.
Most of the fittings used in hydronic radiant heating systems are typical plumbing fittings. They include couplings (standard, slip, and reducing couplings), elbows (both 45° and 90° elbows), male and female adapters, unions, and tees (full size and reducing tees) (see Figure 1-5).
Three special fittings used in hydronic radiant heating systems are the brass adapters, the brass couplings, and the repair couplings. A brass adapter is a fitting used to join the end of a length of ¾-inch diameter copper tubing to the end of a length of plastic polyethylene tubing. A brass coupling, on the other hand, is a fitting used to join two pieces of plastic heat exchanger tubing. A repair coupling is a brass fitting enclosed in clear vinyl protective sheath to prevent concrete from corroding the metal fitting. The fitting is strengthened by double-clamping it with stainless steel hose clamps.
A decoiler bending device or jig should be used to bend metal tubing into the desired coil pattern. Only soft copper tubing can be easily bent by hand. It is recommended that a tube bender of this type be made for each of the different center-to-center spacing needed for the various panel coils in the installation.
Soft copper tubing is commonly available in coil lengths of 40 feet, 60 feet, and 100 feet. When the tubing is uncoiled, it should be straightened in the trough of a straightener jig. For convenience of handling, the straightener should not be more than 10 feet long.
Most copper tubing leaks will occur at bends or U-turns in the floor loops.These leaks are caused by water or fluids under high pressure flowing through the weakened sections of tubing. The weakened metal is commonly caused by improper bending techniques.
Whenever possible, continuous lengths of tubing should be used with as few fitting connections as possible. Coils of 60 feet or 100 feet are best for this purpose and are generally preferred for floor panels. The spacing between the tubing should be uniform and restricted to 12 inches or less. Use soldered joints to make connections between sections of tubing or pipe.
Figure 1-5 Some examples of copper tubing fittings.

Cross-Linked Polyethylene (PEX) Tubing

Cross-linked polyethylene (PEX) tubing is commonly used indoors in hydronic radiant heating panels or outdoors embedded beneath the surface of driveways, sidewalks, and patios to melt snow and ice. It is made of a high-density polyethylene plastic that has been subjected to a cross-linking process (see Figures 1-6, 1-7, and 1-8). It is flexible, durable, and easy to install. There are two types of PEX tubing:
• Oxygen barrier tubing
• Nonbarrier tubing
Figure 1-6 PEX tubing. (Courtesy Watts Radiant, Inc.)
Oxygen barrier tubing (BPEX) is treated with an oxygen barrier coating to prevent oxygen from passing through the tubing wall and contaminating the water in the system. It is designed specifically to prevent corrosion to any ferrous fittings or valves in the piping system. BPEX tubing is recommended for use in a hydronic radiant heating system.
Nonbarrier tubing should be used in a hydronic radiant heating system only if it can be isolated from the ferrous components by a corrosion-resistant heat exchanger, or if only corrosion-resistant system components (boiler, valves, and fittings) are used.
PEX tubing is easy to install. Its flexibility allows the installer to bend it around obstructions and into narrow spaces. A rigid plastic cutter tool, or a copper tubing cutter equipped with a plastic cutting wheel, should be used to cut and install PEX tubing. Both tools produce a square cut without burrs.
PEX tubing can be returned to its original shape after accidental crimping or kinking by heating it to about 250-275°F. This attribute of PEX tubing makes it possible to perform field repairs without removing the damaged tubing section. This is not the case with polybutylene tubing, which is not cross-linked. Synthetic rubber tubing is also not cross-linked, but its material composition and its flexibility make it very resistant to crimping or kinking damage.
Figure 1-7 PEX tubing markings.(Courtesy Vanguard Piping Systems, Inc)
Figure 1-8 PEX tubing fittings. (Courtesy Watts Radiant, Inc.)


A manifold is a device used to connect multiple tubing lines to a single supply or return line in a hydronic radiant floor heating system (see Figures 1-9 and 1-10). Each heating system has at least two types of manifolds: a supply manifold and a return manifold. A supply manifold receives water from the heating appliance (that is, the boiler, water heater, or heat pump) through a single supply pipe and then distributes it through a number of different tubing lines to the room or space being heated (see Figure 1-11). A return manifold provides the opposite function. It receives the return water from the room or space through as many tubing lines and sends it back to the boiler by a single return pipe. A supply manifold and a return manifold are sometimes referred to jointly as a manifold station.
Figure 1-9 Weil-McLain hydronic radiant heating manifold.
(Courtesy Weil-McLain)
Figure 1-10 Monifold combinations.(Courtesy Weil-McLain)
Figure 1-11 Typical manifold location.
Preassembled manifolds are available from manufacturers for installation in most types of heating systems. Customized manifolds can also be ordered, but they are more expensive than the standard, preassembled types.
A supply manifold, when operating in conjunction with zone valves, can be used to control the hot water flow to the distribution lines in the radiant heating system. The zone valves, which are usually ball valves, can be manually adjusted or automatically opened and closed with a zone valve actuator. Some zone valves are designed as fully open or fully closed valves. Others are operated by a modulating actuator that can adjust the opening to the heat required by the zoned space.
A supply manifold with zoning capabilities is sometimes called a zone manifold or distribution manifold. In addition to zone valves, these manifolds also can be ordered to include supply and return water sensors, the circulator, and a control panel with indoor and outdoor sensors.
Depending on the heating system requirements, a manifold may also include inline thermometers or a temperature gauge to measure the temperature of the water flowing through the tubing; check valves or isolation valves to isolate the manifold so that it can be serviced or repaired; drain valves to remove water from the manifold; an air vent to purge air from the system; and pump flanges (for the circulator) plus all the required plumbing connections and hardware.
Manifold balancing valves regulate each zone (loop) to ensure efficient heat distribution and eliminate those annoying cold and hot spots on the floor. These valves can be adjusted to deliver the design flow rate of water in gallons per minute (gpm). Some manifolds are designed to electronically read the flow and temperature of the water in individual tubing loops. This function results in rapid and accurate data feedback for balancing. It also makes troubleshooting problems easier.
Manifolds are available for mounting on walls or installation in concrete slabs. The latter type, sometimes called a slab manifold, is made of copper and is available with up to six supply and six return loop connections. Slab manifolds also should be equipped with a pressure-testing feature so that they can be tested for leaks before the slab is poured.
Slab manifolds are installed with a box or form that shields the device from the concrete when it is poured. All connections remain below the level of the floor except for the tops of the supply and return tubing.

Valves and Related Control Devices

Valves and similar control devices are used for a variety of different purposes in a hydronic radiant floor heating system. Some are used as high-limit controls to prevent excessively hot water from flowing through the floor loops. Some are used to isolate system components, such as the circulating pump, so that it can be serviced or removed without having to shut down the entire system. Others are used to regulate the pressure or temperature of the water, to reduce the pressure of the water before it enters the boiler, or to regulate the flow of water.
Many of the different types of valves and control devices used in hydraulic radiant floor heating systems are listed in the sidebar. A brief description of the more commonly used ones is provided in this section. For a fuller, more detailed description of their operation, maintenance, service, and repair, read the appropriate sections of Chapter 9 (“Valves and Valve Installation”) of Volume 2. Not all the valves listed in the sidebar or the ones described in this chapter will necessarily be used in the same heating system. The valves chosen will fit the requirements of a specific application (see Figures 1-12, 1-13, and 1-14).
Hydraulic Heating System Valves and Related Control Devices
• Air vent
• Aquastat
• Backflow preventers
• Ball valves
• Boiler drain valve
• Check valves
• Feed water pressure regulator
• Flow control valve
• Gate valve
• Globe valve
• Isolation valve
• Mixing valve
• Motorized zone valve
• Pressure-reducing valve
• Pressure relief valve
• Purge and balancing valves
• Solenoid valve

Air Vent

An air vent is a device used to manually or automatically expel air from a closed hydronic heating system. An automatic air vent valve provides automatic and continuous venting of air from the system. The function of both types is to prevent air from collecting in the piping loops.
Figure 1-12 Typical locations of valves and related control devices in a hydronic heating system. (Courtesy Watts Regulator Co.)


An aquastat is a control device consisting of a sensing bulb, a diaphragm, and a switch (see Figure 1-14). As the temperature surrounding the sensing bulb increases, the gas inside the bulb expands and flows into the diaphragm. This action causes the diaphragm to expand and activate the switch controlling the connected device. When temperatures exceed the high-limit setting on the aquastat, it shuts off the circulator or circulators until the problem can be corrected.
Fig 1-13 Piping if a zoned radiant heating system suppling hot water to both floor panels and daseborards.
Figure 1-14 Piping diagram of a radiant heating system with circulator controlled by aquastat.
The switching contacts of some aquastats can be manually adjusted for temperature settings. In other systems, the switching contacts of an aquastat may be preset at a predetermined temperature setting.

Backflow Preventer

A backflow preventer is a valve used to prevent the mixing of boiler hot water with domestic (potable) water (see Figure 1-15). Most systems use an inline backflow preventer. It must be installed with the arrow on the side of the valve facing the direction of water flow. Sometimes a backflow preventer and boiler fill valve are combined in the same unit.

Ball Valve, Gate, and Globe Valves

A ball valve can be used to isolate components or lines, or to regulate flow. A gate valve is often used to isolate components for service, repair, or replacement. They are not designed to regulate the flow of water. A globe valve is used to regulate the flow of water in a radiant heating system.
Use a fully closing ball or gate valve on the supply and return line so that the manifold can be isolated and serviced without interrupting the pressure in the rest of the system.
Figure 1-15 Feed water pressure regulator. (Courtesy Watts Regulator Co.)

Boiler Drain Valve

A boiler drain valve is a quarter-turn ball valve used to drain water from a boiler. As shown in Figure 1-12, it is located near the bottom of the boiler close to a floor drain.

Check Valves

A check valve (also called a shutoff valve) is used to ensure that water is flowing in the correct direction by providing positive shutoff to the flow. Typical locations of check (shutoff) valves are shown in Figures 1-12, 1-13, and 1-14.
A swing check valve is designed to prevent the backflow of water. A flow-control valve is a check valve used to prevent circulation of the hot water through the heating system when the thermostat has not called for circulation. The flow-control check valve must be used when the radiant panels are located below the boiler.
Flow-control valves should not be used when the radiant floor panel is below the level of the boiler.
Another type of check valve used in a radiant floor heating system is the isolation valve (also sometimes called a service valve).
The isolation valve is used to isolate a hydronic system component for servicing and/or removal so that it can be repaired or replaced. Isolating the component eliminates the need to drain and refill the system with water.
Reduce the system pressure to a safe level before attempting to remove system components.
An isolation valve is not designed to isolate a pressure (safety) relief valve or other safety or flow-sensitive components.

Feed Water Pressure Regulators

A feed water pressure regulator is used to fill both the boiler and system piping (including the floor panel loops) with water. A typical location of a feed water pressure regulator in the cold-water return line is illustrated in Figure 1-15. These valves also maintain the water pressure at the required level in the system at all times. If a leak should occur in the system, the feed water pressure regulator is designed to provide the required amount of makeup water. Using the feed water pressure regulator speeds filling and purging of air from the piping during the initial fill procedure.

Disconnect Switch

Two principal types of on-off switches are used to open or close an electrical circuit: the disconnect switch and the thermostat (see Thermostat in this section).
The disconnect switch is a manually operated on-off switch used to shut down the entire heating system when a problem is beginning to develop. When the switch is in the off position, the circuit opens and the electricity operating the boiler, heat pump, or water heater is shut off. When it is in the on position, the circuit closes (that is, completes itself) and electricity bypasses the boiler, heat pump, or space-heating water heater.

Inline Thermometer

An inline thermometer is a device that is used to monitor the water temperature as it circulates through the system. Two inline thermometers are installed in the heating system. One monitors the temperature of the water as it enters the supply line. The other monitors the temperature of the water as it leaves. The difference between these two measurements provides clues to the operating efficiency of the system.

Mixing Valve

A thermostatic mixing valve is used in a radiant heating system to recirculate a variable portion of the return water and at the same time add a sufficient quantity of hot boiler water to maintain the required water temperature in the loops. These valves are also called thermostatic mixing valves, water blending valves, water blenders, water tempering valves, or tempering valves. Typical locations of mixing valves are shown in Figures 1-12, 1-13, and 1-14.
Both manual and automatic modulating mixing valves are used in hydronic heating systems. The manual mixing valve is often used to control the water temperature in a high-mass concrete slab. It is not as accurate as an automatic valve (for example, a thermostatic valve), but the high-mass concrete slab stores it and releases it slowly over a long period of time, making exact temperature control unnecessary.
The three-way and four-way thermostatic mixing valves provide automatic control of the mixed water temperatures. The valve varies the flow of hot water between its hot port and its cold port so that it can deliver through its mixed port a steady flow of water at a constant temperature.
Mixing valves are often used with high-temperature boilers designed to provide water at temperatures of more than 160°F.

Motorized Zone Valve

A motorized zone valve is used to control the flow of water through a single zone (see Figure 1-16). It consists of a valve body combined with an electric actuator. A radiant panel heating system will often use a number of motorized zoning valves to maintain a uniform temperature throughout the rooms and spaces in the structure. As shown in Figure 1-17, a motorized zone valve is used to control each zone. Motorized zone valves are controlled by an aquastat, individual thermostats at each loop, or a room thermostat.
Figure 1-16 Honeywell V4043 motorized zone valve.
(Courtesy Honeywell, Inc.)
Figure 1-17 A typical control system for a multiple-zone radiant heating system. (Courtesy Honeywell Tradeline)
A zone valve simplifies the piping required for a hydronic heating system because it eliminates the need for a flow check valve and relays.

Pressure-Reducing Valve

A pressure-reducing valve is designed to reduce the pressure of the water entering the system and to maintain the pressure at a specific minimum setting (usually about 12 lbs). A typical location of a pressure relief valve is shown in Figure 1-12.

Pressure Relief Valve

A pressure relief valve (also sometimes called a safety relief valve) is used to prevent excessive and dangerous pressure from entering the system. It is located on top of the boiler or very close to it (see Figures 1-12, 1-13, and 1-14).

Purge and Balancing Valves

Purge and balancing valves are used on either the supply or return side of the manifold in systems where multiple manifolds are served by only one circulator. Among its varied functions is (1) to allow adjustments of proper water flow for each loop; (2) to function as a shutoff valve and a drain valve for each zone or loop; (3) to control (balance) water flow through the circulation loop; and (4) to provide a means of expelling air from heating zones during initial loop fill (valve is located on the boiler return piping). If the heating system contains individual loops of unequal length, each should be equipped with a balancing valve.


The circulator (circulating pump) provides the motive force to circulate the water through the radiant heating system. Sometimes a variable-speed pump is used to maintain a supply water temperature between 90°F and 150°F.
In some zoned systems, a circulator operates in conjunction with a zone thermostat instead of a zoning valve to maintain a uniform floor temperature in each room or space of the structure. The zone thermostat controls the temperature in the zone by turning the circulator on and off. The size of the circulating pump selected for a radiant panel heating system will depend on the pressure drop in the system and the rate at which water must circulate. The circulation rate of the water is determined by the heating load and the design temperature drop of the system and is expressed in gallons per minute (gpm). This can be calculated by using the following formula:
The total heating load is calculated for the structure and is expressed in Btu per hour. A value of 20°F is generally used for the design temperature drop (T) in most hot-water radiant panel heating systems. The other two values in the formula are the minutes per hour (60) and the weight (in pounds) of a gallon of water (8).
By way of example, the rate of water circulation for a structure with a total heating load of 30,000 Btu per hour may be calculated as follows:

Expansion Tank

An expansion tank (also called a compression tank) is required for use in all closed hydronic radiant heating systems (see Figure 1-18). Water and other fluids expand when they are heated. The expansion tank provides space to store the increased volume to prevent stress on the system.

Air Separator

An air separator (also called an air scoop or an air eliminator) is a device used in a closed radiant heating system to capture and remove air trapped in the water (see Figure 1-18). Some of these devices are equipped with tappings for the installation of an expansion tank and air vent.
Figure 1-18 Air separator and expansion tank.

Heat Exchanger

A heat exchanger is a device used in some radiant heating systems to separate dissimilar fluids such as water mixed with antifreeze (in snow- and ice-melting applications) and water (for radiant floor heating tubing and domestic hot water). Its function is to allow the transfer of heat between the fluids without allowing them to mix and thereby contaminate one another.

Automatic Controls

While any thermostatic method of control will function with a radiant floor heating system, the most desirable method is one based on continuously circulating hot water. The temperature of the water should be automatically adjusted to meet outdoor conditions, but the circulation itself is controlled by interior limiting thermostats instead of the simple off-on method of circulating hot water at a fixed temperature (see Figure 1-19).
Some radiant floor heating systems are designed with a thermostat for each zone (see Figure 1-17). A more common method is to group several rooms or spaces together and control them by a single thermostat. In this approach, the kitchen and dining room may be included in one thermostat-controlled loop, the bedrooms in another, the bathrooms in still another, and so on.
Figure 1-19 Examples of thermostat controls used in hydronic radiant heating systems.
Many HVAC control manufacturers are now producing control consoles such as the one shown in Figure 1-20.

Designing a Hydronic Radiant Floor Heating System

Design of a hydronic radiant floor heating system should be attempted only by those with the qualifications, training, and experience to do it right. It is very important that the design of a radiant panel heating system be correct at the outset. The fact that the coils or cables are permanently embedded in concrete, or located beneath other materials, makes corrections or adjustments very difficult and expensive.
Many manufacturers of radiant panel heating system equipment have devised simplified and dependable methods for designing this type of heating system. In most cases, the manufacturer will provide any available materials to assist in calculating the requirements of a particular radiant floor heating system. Various design manuals, manufacturer-specific installation guides, and software tools are available for use in designing and sizing radiant floor heating systems.
A radiant floor heating system in which there is a constant (uninterrupted) circulation of water is the preferred design. The benefits of constant water circulation through the circuits are as follows:
• It maintains an even floor temperature.
• It prevents hot spots from forming when there is no call for heat.
• It prevents air from entering the system.
• It reduces the risk of the water freezing in systems where antifreeze cannot be used (that is, systems in which the water heater heats both the water for space heating and the water for cooking and bathing purposes).
Figure 1-20 Watts Boiler Energy Saver and wiring diagrams. (Courtesy Watts Regulator Company)
The flow of water in some radiant heating systems is controlled by the circulator (pump). When the room thermostat calls for heat, the pump starts and rapidly circulates heated water through the radiant panels until the heat requirement is satisfied. The pump is then shut off by the thermostat. In some systems, a flow-control valve is forced open by the flow of water through the pipes as long as the pump is running, permitting free circulation of heated water through the system. When the pump stops, the control valve closes, preventing circulation by gravity, which might cause overheating. The principal disadvantage of a system with this off-on control is that it results in temperature lag and causes the panels to intermittently heat and cool.
The continuous circulation of water through radiant heating panels is made possible by means of an outdoor-indoor control.
In this arrangement, hot water from the boiler is admitted to the system in modulated quantities when the temperature of the circulating water drops below the heat requirement of the panels. This modulated bleeding of water into the panel is accomplished through a bypass valve. When no additional heat is required, the valve is closed. When more heat is required, the valve is gradually opened by the combined action of the outdoor temperature bulb and a temperature bulb in the supply main. This system gives control by the method of varying the temperature of the water.

Air Venting Requirements

A common defect encountered in hot-water system design is improper venting. The flow of water should be automatically kept free of air binding throughout the system. Air in the pipes or pipe coils almost always results in a reduction of heat.
A practical method of venting is shown in Figure 1-21. The key to this method is the use of automatic air vents. Each air vent should be located in an area readily accessible for repair. The air trap test cock should be placed where it can be easily operated. Both the air trap and the air trap test cock must be located where they are not subject to freeze-up, as both are noncirculating except during venting operation (automatic or manual).

Sizing Calculations

The successful operation of any hot-water heating system requires the incorporation of design provisions that ensure an even and balanced flow of water through the pipes or coils of the installation.
The procedure for designing a hydronic radiant floor heating system may be outlined as follows:
1. Determine the total rate of heat loss per room in the structure.
2. Determine the available area for panels (loops) in each room.
3. Determine the output required by each panel to replace the heat loss.
4. Determine the required surface temperature for each panel.
5. Determine the required heat input to the panel (should equal heat output).
6. Determine the most efficient and economical means of supplying heat to the panel.
7. Install adequate insulation on the reverse side and edges of the panel to prevent undesirable heat loss.
8. Install the panels opposite room areas where the greater heat loss occurs.
Figure 1-21 An automatic vent radiant heating system.
Always keep floor temperatures at or slightly below recommended high limits.

Radiant Floor Construction Details

Radiant floor construction can be divided into two broad categories based on the installation method used: (1) wet installation and (2) dry installation. The wet installation method involves completely embedding the tubing in a concrete slab or covering it with a thin layer of concrete (commonly a gypsum-based lightweight pour).
The dry installation method is so-called because the tubing is installed without embedding it in concrete.
The examples of radiant floor construction described in this section represent the most commonly used forms. They are offered here only as examples, not as planning guides for contractors. The actual construction plans will depend on the design of the hydronic radiant floor heating system, the impact of local building codes and regulations, and other variables.

Slab-on-grade construction

In slab-on-grade construction, the tubing is attached to a wire mesh or special holding fixtures to keep it in place until the concrete is poured around it. The tubing loops are embedded in the middle of the concrete slab and are located approximately 2 inches below the slab surface (see Figure 1-22). A brief summary of the steps involved in slab-on-grade construction is as follows:
1. Compact the soil base to prevent uneven settling of the slab.
2. Cover the compacted soil with a lapped 6-mil vapor barrier.
3. Cover the vapor barrier with 2-inch-thick extruded polystyrene insulation.
4. Install rigid polystyrene insulation vertically on the inside surface of the exterior foundation walls to prevent edgewise (horizontal) heat loss.
5. Lay concrete reinforcing mesh over the insulation.
6. Position the tubing on top of the reinforcement mesh according to the tubing layout plan.
7. Tie the tubing to the reinforcement mesh with tie straps or wire.
8. Cover the tubing with a minimum of 9 inches of concrete.

Thin-Slab Construction

In this type of wet installation, a layer of lightweight concrete or lightweight gypsum is poured over the tubing to form a thin slab (see Figure 1-23). Thin-slab construction is used over a wood subfloor supported by wood framing.
A summary of the steps involved in forming a thin-slab floor system using poured concrete to form the slab may be outlined as follows:
1. Apply a lapped 6-mil polyethylene vapor barrier to the wood subfloor.
2. Position the tubing on the subfloor according to the tubing layout plan.
4. Pour concrete over the tubing and subfloor.