Sheet Metal Duct
Galvanized steel or aluminum air ducts can be round, oval, or rectangular like the one Bruce Willis crawls through in Die Hard. Sheet metal HVAC ductwork is the most durable and least likely to harbor mold. Metal air ducts are practically rustproof, especially galvanized steel with its zinc coating.

Flex Duct
Simply put, flex ducts are made from a steel wire spiral, wrapped with a polymer (a bendable plastic), and surrounded by insulation. This kind of ductwork is inexpensive, lightweight, and easy to install. Flex ducts work wonders in tricky spaces where more rigid ductwork will not do.

Fiberboard Duct
This type of duct has two layers: compressed resin-bonded inorganic fiberglass is encased in foil to prevent air and water vapor from penetrating. Typically, this air duct is the least expensive, prevents noise, and is already well insulated. The downside? The rough fiberglass surface inhibits airflow.

Beware – old fiberboard ducts aren’t treated to prevent mold or mildew and should be replaced immediately. If you suspect you have old fiberboard ductwork, do not attempt to clean it. The surface damage will release fiberglass into the air and throughout your home.

1. Install the ductwork starting with the unit. Use the sheet metal kind and duct tape to wrap around every joint. It will seal it tightly.
2. If you can, run some ductwork among the floor joists. Hold it in place using galvanized hanging straps.
3. Add the pieces that approach every vent or that register in your home.
4. It’s time to add the return ductwork. Start at the main unit once more. Work your way out just like you did the first time.
5. Turn the thermostat as high as it can go to test the ductwork you’ve just installed.

• Not installing a support for the flex ducts every four feet. That could cause the ductwork to sag, which might mean that the air flow is a lot lower while the friction could be higher.
• Not insulating the supply lines in their entirety. It’s not enough for the spaces the ductwork goes through to be insulated, the ducts have to be so as well.
• Not fastening two pieces of ductwork together with a rigid connector. Don’t just flex them inside each other.
• Don’t forget to insulate the butt joints. If you do, then the supply air could leak out.
• Not testing the ductwork after installing it. This could lead to serious issues not being discovered until it’s too late.

checkout our Homeowner’s Guide to Ductwork to learn more.

Check this out – there are 4 common air duct designs.

The first is the plenum or radial duct system. Radial systems have the HVAC unit and return grill at the center of the home with the supply ducts extending out around the plenum like the legs of a spider.

The second is the reducing extended plenum system. As the name implies, the plenum reduces in size as it extends across with the air ducts coming out from either side.

The third is the extended plenum system. This time the plenum, which does the distribution or removal of air for the HVAC unit, does not reduce in size as it extends across.

The last is the perimeter loop system – a radial system, not as many spider legs, with a supply duct that encircles the building.

Learn about Duct Design Problems here

1. Think about the type of equipment and supporting systems
There are some kinds of units, such as heat pumps that might need you to install larger ducts. Or, if the system you want has air purifiers that have filters with activated charcoal, you will also need larger ducts as well as more air returns.

2. Calculate the load in detail
This becomes especially important if you have more than one room that will need to be heated or cooled differently at the same time. In this scenario, you should calculate the load for each of those rooms and not for the whole house at once.

3. What’s the best place to put your unit and ducts?
If you have planned this out properly, than the HVAC unit should have a somewhat centralized position. This will minimize the length of the ducts. Speaking of which, they need to sit in the ceiling and internal walls so that no air will be lost. If possible, avoid installing your ducts in crawl spaces or in the attic so that you don’t waste any conditioned air.

4. Find the proper materials
This of course, includes the supports and fittings. It will depend greatly on the budget you have as well as your needs, but even so you should always make sure your technician uses only the top quality ducts.

5. Make sure everything is perfectly sealed
If the joints have not been sealed correctly, then up to 20% of the air may be lost in transition. Therefore, you need to use mastic gum or even metal-backed tape as an alternative.

In HVAC systems, your air goes through a cycle. A negative pressure in the ducts sucks the air in, passing it through a filter. The cleaned air is heated or cooled and sent back to the areas of your house where it stays until it’s cycled again. Return and Supply Ducts are critical in the movement of airflow.

Return Ducts
Contrary to popular belief, HVAC systems get their air from inside the building. Return ducts extract air from the living spaces back to the HVAC unit, feeding either your furnace or air handler. Return vents are usually larger than supply vents and are called grills. A filter is often installed either deep inside a return duct or right at the return grill to protect your HVAC unit from impurities.

Supply Ducts
Supply ducts blow warm or cool air to an area inside a home. Supply vents often have dampers to control the flow, called registers. Supply registers will often be installed near windows or doors to better counteract the loss of heat or cold, and two supply registers may be installed in larger rooms to evenly distribute the HVAC air.