What is HVAC Piping? Types and Materials for HVAC Piping (PDF)

HVAC piping or heating ventilation and air-conditioning piping deliver hot water, cool water, refrigerant, condensate, steam, and gas to and from the HVAC components. HVAC systems provide thermal comfort for the occupants accompanied by indoor air quality. They are used in industrial, commercial, residential, and institutional buildings for different purposes like

  • To add or remove heat from the air inside the building. 
  • Control the humidity. 
  • Filter the air in the building. 
  • Bring fresh air into the building.

So, for this process HVAC Piping systems use chilled water, hot water, condensate water, condensate drainage, refrigerant, steam, and gas to deliver from HVAC equipment using piping networks. Using HVAC piping in HVAC systems is highly efficient and affordable.

The cooling system consists of chilled water and condensate water. Chilled water systems pump water in a closed-loop and never get mixed with other condensate water. Heat is absorbed and passed off at three main points in the chilled water systems. The first point is the fan coil unit which is located throughout the buildings. The next one is the chiller which uses a refrigerator to cool the chilled water and acts as a heat exchange and the next one is the condensate water system acting as an open loop. Which exposes the water to the atmosphere at the cooling towers.

The heating system, which is capable of adding heat to the occupied space adds up both the steam system and the hot water system. Which uses a boiler to produce the steam usually fired up by natural gas or fuel oil. Boiler pressure is used to force the steam through the piping system to a heat exchanger. Inside the heat exchanger, the heat is transferred into the hot water and is carried to the occupied space. Steam traps are used to collect the condensate after the steam has given off its heat and allowed it to condensate back to a liquid state. condensate pumps are used to pump the condensed water back to the boiler to proceed again. The next one is the hot water system which is also a closed-loop system. Which gets its heat from the heat exchanger and is pumped into the spaces within the buildings which are to be heated. These cooling and heating piping networks are collectively called HVAC piping systems.

Types of HVAC Piping System

HVAC Piping system can be classified into two parts; the piping in the central plant equipment room and the delivery piping. The central plant equipment room consists of the pipe networks connected to the rotating equipment and tanks. They are connected to different types of equipment like heat exchangers and pumps over the pump room from these regions the piping network transports the process liquid to the other parts of the building using the delivery piping. 

HVAC Piping Materials

The effectiveness of the piping gets influenced by the materials used to make it. Copper and steel are the two major types of metals used for HVAC piping.  Copper is used mostly for smaller piping, transporting water in ac unit with a maximum commercial size of about 12 “as the use of copper is very expensive than that of other materials available. So that the piping used in HVAC is 3 “and smaller. 

Steel on the other hand is much cheaper and is used for large sizes. It can also withstand higher pressure than copper and is ideal for both hot and cold water. It usually allows for a range of temperature and pressure. Sch 40 and Sch 80 pipes of the same are acceptable for several HVAC applications.

For chilled and heating water services 8” and above, ASTM A53 or A135 (light wall black steel pipe) are used.

ASTM A120 and A53 (black steel pipe Sch. 40) are used up for services like

  1. Chilled and heated water piping
  2. Miscellaneous drains and overflows
  3. Emergency generator exhaust
  4. Safety and relief valve discharge
  5. Chemical treatments
  6. High- and low-pressure steam
  7. Steam vent

ASTM 120 and A53 Sch. 80 (black steel pipe) get used for pumped and gravity steam condensate return.

ASTM A120 Sch. 40 (galvanized steel pipe) can be used up for miscellaneous indirect wastewater pipes.

ASTM B88 (copper pipe) used for,

  1. Industrial cold water (above grade-type L) for piping 4 “and smaller.
  2. Refrigerant piping (type L, hand-drawn) below 6“
  3. Chilled and heating water (type L and hand-drawn) below 3”.

Underground pipes need to go cathodic protection to prevent corrosion from dirt. Which is coating it in a thin layer of some other metal such as zinc to absorb the corrosion. Flanges used are per ANSI B16.1. Cast iron or steel are used for screwed pipe and forged steel welding necks are used for welded line sizes.

Plastic piping, which is much cheaper than copper and steel is another common material used for HVAC applications. They are thinner and weaker and won’t be able to withstand much pressure. It doesn’t get corrode which makes it suitable for underground uses. PVC and CPVC are the two types of plastic piping commonly used. They won’t be able to withstand a wide range of temperatures as metal.

HVAC Piping Insulation

Depending upon the existing code conditions they may or may not be insulated. Usually, they are insulated with closed-cell elastomeric foam pipe insulations due to their closed cell structure and built-in vapor barrier. They range from -297°F to +220°F HVAC pipe services.

They are also different type of insulations like mineral fiber insulation (glass fibers bonded with thermosetting resin) which includes

  • Preformed pipe insulation (comply with ASTM C547)
  • Blanket insulation (ASTM C553)
  • Fire-resistant adhesive
  • Vapour retarder mastics
  • Mineral fiber insulating cement (ASTM C195)

Prefabricated thermal insulating fitting covers (ASTM C450) and elastomeric cellular thermal insulations (ASTM C 534).

Buried HVAC piping parts are wrapped in accordance with AWWA C209 and C214.

Analyzing HVAC Piping Systems

Analysis of the system includes checking the piping system for its compliance with code requirements in stresses under different loading conditions. Operating conditions will be design temperature, ambient temperature, operating temperature, design pressure, and hydro test pressure. Materials required are selected accordingly as per the process parameters. Sometimes, expansion compensators are used to accommodate the expansion and contraction of the HVAC piping network.

In these cases, mostly ASME B31.9 (utility service piping) is used, sometimes B31.3 and B31.4 for underground piping. 

Verifying the displacement and loads on supports in the overall systems. usually, the plastic piping will have more displacements due to its elastic properties. Quality assurance must also be made sure. The piping material and installation shall meet the requirements of the local building codes and service utility requirements.

Support Spacing of HVAC Piping System

The usual support span for horizontal HVAC piping systems are provided in the table below:

Pipe SizeMaximum Support SpacingCommon Hanger Diameter if supported using Rigid hangers
1/2 to 1-1/4 inches (12.7 to 31.75 mm)6 feet 6 inches (2 m)3/8 inch (9.5 mm)
1-1/2 to 2 inches (38.1 to 50.8 mm)10 feet (3 m)3/8 inch (9.5 mm)
2-1/2 to 3 inches  (63.5 to 76.2 mm)10 feet (3 m)1/2 inch (12.7 mm)
4 to 6 inches (101.6 to 152.4 mm)10 feet (3 m)5/8 inch (15.9 mm)
8 to 12 inches (203.2 to 304.8 mm)14 feet (4.25 m)7/8 inch (22.2 mm)
14 inch (355.6 mm) and over20 feet (6 m)1 inch (25 mm)
PVC (All sizes)6 feet (1.8 m)3/8 inch (9.5 mm)
C.I. Bell and Spigot (or No-Hub)5 feet (1.5 m) at joints3/8 inch (9.5 mm)
Table 1: Support Span for HVAC piping systems

Horizontal Cast iron HVAC pipes are supported adjacent to each hub, with 5 feet (1.5 m) maximum spacing between supports/hangers. Vertical HVAC pipes are generally supported on every floor. Vertical cast iron pipes are supported at each hub.

Joining HVAC Piping

Usually, the following guidelines are followed for joining HVAC piping during installation:

  • HVAC piping systems are joined using the method suggested by the manufacturer in accordance with applicable codes and standards.
  • For copper HVAC piping Soldered joints are used.
  • For steel HVAC piping, Screwed, Flanged, or Welded joints are used.

HVAC Piping Frequently Asked Questions with Answers

What is HVAC piping made of?

HVAC piping is usually made of Steel, Copper, or PVC. For smaller pipes, Copper is used. In general, copper as an HVAC piping material is selected for lines below 3 inches.

What type of pipe tubing is most common in the HVAC industry?

The most widely used HVAC pipe tubing is made up of copper. They are widely used in both refrigerant and heating systems. However, recently, PEX tubing is replacing copper tubing in cold and hot water applications.

What is a two-pipe HVAC system?

Two pipe HVAC system is a cost-effective HVAC piping solution that uses the same piping system alternately for chilled water cooling and hot water heating.

What type of pipe is used for chilled water?

For chilled water piping systems, Steel pipe is the most widely used material.

What type of copper pipe is used for HVAC?

Type L Copper pipe that is available in rigid as well as flexible forms are used in HVAC piping systems.

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Adarsh

Myself a mechanical engineering graduate. I am so much passionate about blogging and engineering which brought me over here. Currently working as a pipe stress analysis engineer for a reputed firm.

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