PVC pipe is one of the most common materials used in construction. While it's mostly used for plumbing purposes, PVC is also a valuable component in the heating and cooling industry. While HVAC ducts are typically made of sheet metal, PVC ducts also come in handy in certain situations. However, in order to use PVC duct effectively, you must use the proper materials and methods to join the individual sections together.
Joining and installing PVC duct isn't like joining other types of duct. Rather than tape and special pieces of sheet metal, you need primer, cement glue, screws, and other tools and materials. It's essential that you complete the process properly, otherwise, you will have inefficiencies, unclean air, and other issues.
If you're interested in using PVC duct but don't know the first thing about how to install it or when to use it, you've come to the right place. This article will provide detailed instructions about how to join PVC ducts together when to use them, and alternatives when PVC isn't the right material.
What is PVC Duct?
A PVC duct is a special type of heating and cooling duct made of PVC. Like PVC pipes used in plumbing, PVC ducts are round and consist of polyvinyl chloride. However, PVC ducts are typically much larger, usually between 6" and 12" in circumference, since their job is to disperse air rather than liquid or waste.
Different Types of PVC Ducts
As with all other forms of heating and cooling equipment, there are several different types of PVC ducts you can use. This includes standard PVC pipe, PVC mixed with other plastics, and potentially even incorporating metal and rubber components into the mix.
Standard PVC Pipe
Standard PVC (polyvinyl chloride) is the most common material used with PVC HVAC ducts. However, as with plumbing pipes, there are different levels of wall thickness with PVC ducts. The thicker the PVC, the more durable and efficient it will be. However, thick PVC ducts are also heavier, which makes them more expensive and difficult to install.
Incorporating Metal Fittings
Some HVAC installers also incorporate metal and rubber fittings with PVC pipe during installation. In most cases, this will mean using metal and rubber elbows, 45s, couplers, and other fitting joints to join pieces of PVC pipe together. The main reason to do this is because metal and rubber fittings are cheaper than PVC, but you could be compromising quality for affordability.
Common Applications For PVC Duct
PVC duct gets used with traditional split systems where you have a furnace and/or air conditioner that distributes air through a home or business. The PVC pipe gets attached to the top or side of the furnace, and there is a main trunk line with smaller individual "runs" coming off of it. You can use PVC duct in the following ways:
Underground Applications
The main place that PVC duct is used is in underground applications, where the ductwork is located in the slab of a house. In these instances, the PVC duct is one of the first things installed on the home, and it then gets sealed inside the poured concrete slab.
Crawl Spaces
You can also use PVC duct in crawl spaces where traditional duct could create condensation. Some crawl spaces are also tight enough that traditional sheet metal ducts aren't a good fit.
Attics
Finally, PVC ducts are a great option for attics for the same reasons why they are a good option for crawl spaces. Most forms of PVC don't require insulation, and they don't "sweat," which cuts down on installation time.
How to Join PVC Duct Sections: A Step-by-Step Process
Now that you know more about what PVC duct is and where you can use it, let's look at how to join and install it!
1. Measure Before Cutting
Depending on what type of PVC duct you use, it can be fairly pricey. As such, it's important to always measure precisely before cutting your pipes so that nothing goes to waste. Most of the time, you'll be able to install full sections of pipe.
However, there will be instances when cutting is necessary, so be prepared. It's also a good idea to dry fit the pieces together to ensure they fit.
2. Clean the Edges
If you're installing a full section of pipe with factory ends, you don't need to worry about this step. However, if you had to cut the pipe using a Sawzall or another tool, use your hand or a piece of sandpaper to rub around the edges of the pipe and clear away any burrs.
3. Apply Primer
With the edges clean, smear PVC primer or solvent around the outside of the pipe to clean the area. Do the same to the female end of whatever fitting you're inserting the pipe into.
4. Apply PVC Cement or Glue
After applying primer, immediately apply PVC cement that's specifically meant for PVC duct. Standard PVC glue and primer might be too corrosive and eat through the pipes. Be generous with the amount of PVC cement you apply to ensure a strong bond so that your pipes stay together permanently.
5. Join the Sections
With the male end of the pipe and the female end of the fitting primed and cemented, join the sections together. Push the pipe into the fitting as far as it will go and give it a quarter turn as you're inserting the pipe. This will help to ensure a strong connection.
6. Have a Backstop or Helper
It takes more pushing and pressure to connect PVC pipes and fittings together than it does with standard plumbing pipes. Therefore, you'll likely need a backstop or a helper for assistance.
7. Hold the Pieces Together
After fully inserting the pipe and giving it a quarter turn, hold both the pipe and fitting in place for 30 seconds to give the glue time to set.
8. Use Screws For Good Measure
As an insurance policy, you can insert three or four screws through the pipe and fitting to ensure they stay together forever.
9. Tape When Necessary
If local building code requires it, you can also tape around any connected joints. This is especially important for any PVC duct used above ground, as duct sealed in concrete is less likely to have airflow inefficiencies.
Is This Process Always the Same Regardless of Duct Type?
In general, the process of attaching PVC pipes and fittings is the same for all types of PVC duct. The only exception is if you use metal fittings with plastic pipes. In this case, you will use a special adhesive sealing caulk around joints instead of PVC cleaner and cement. It's also more important to screw the joints together when you use metal fittings.