Expert Tips for Properly Sealing and Insulating Ducts

Learn from an HVAC expert about the importance of properly sealing and insulating ducts for improved efficiency, comfort, and health.

Expert Tips for Properly Sealing and Insulating Ducts

As an expert in the field of HVAC systems, I have gained extensive knowledge and experience on the importance of properly sealing and insulating ducts. Not only does it improve the efficiency of the system, but it also ensures the comfort and health of the occupants. In this article, I will share my expertise on which ducts are not required to be sealed and insulated, and why it is still a good idea to do so.

Which Ducts Do Not Need to be Sealed and Insulated?

According to building codes, all ducts, air handlers, and filter boxes must be sealed. However, not all HVAC systems require insulation.

Ducts located in conditioned spaces do not need to be insulated, but they must still be sealed. This includes supply or return ducts located in the conditioned space and return ducts located in a ventilated attic. It may seem counterintuitive to not insulate ducts in conditioned spaces, but there is a reason for this exception. In order for a building to have adequate ventilation, windows must be open near the bottom and top of the walls to allow for warm air near the roof and cold air near the bottom. By not insulating these ducts, it allows for this natural ventilation to occur.

The Importance of Sealing Ducts

While insulation may not be necessary for some ducts, sealing is crucial for all ducts.

The heat transfer constant between zone A and the outside is 2 hours, while between zone B and the outside it is 4 hours. This means that any air leakage from unsealed ducts can significantly impact the efficiency of the system. Furthermore, unsealed ducts can also lead to health issues for the occupants. Air leakage can cause pollutants and allergens to enter the duct system, which can then be circulated throughout the building. This can lead to respiratory problems and other health concerns.

The Role of Duct Testing

In order to ensure that ducts are properly sealed, it is important to have them tested.

This is where a HERS (Home Energy Rating System) evaluator comes in. Before installing drywall, a HERS evaluator must visually inspect the duct system to ensure that all connections are properly closed and sealed. This is preferably done with putty, as it provides a more secure seal than tape or mastic. It is also important to coordinate the layout of ducts with the design of the structure and other systems. This ensures that there is enough space for adequate layout and that the ducts remain inside the conditioned space.

Alternative Options for Duct Placement

In some cases, it may not be possible to keep all ducts within the building envelope.

False ceilings and ceilings can hide ducts while still allowing them to remain inside the conditioned space. However, if any ducts are outside the thermal envelope, a duct testing must be performed to determine the total leak. Figure 1: Duct distribution systems located within the boundaries of the house's thermal and air barrier or in a location optimized for comparable performance.

The Importance of Proper Planning

As an expert, I cannot stress enough the importance of proper planning when it comes to duct placement. By requiring air to be isolated, sealed, and tested as they leave the house's conditioned space, building regulations discourage the placement of ducts in these areas. Unfortunately, this is still a common problem that I see during energy audits. C) Continuously welded and blockage-type longitudinal joints and joints in ducts that operate less than 2 inches away.

In fact, of all the new homes I've tried that haven't passed the ventilated door tests required by the code, all had ductwork in attics or tight spaces without air conditioning.

The Importance of Proper Maintenance

Repairing leaking ducts and duct insulation problems becomes much more difficult and costly once construction is complete. This is why it is crucial to properly seal and insulate ducts during the initial installation process. It is also important to regularly maintain and inspect ducts to ensure they remain in good condition.


While not all ducts need to be sealed and insulated, it is still a good idea to do so. By properly sealing and insulating ducts, it improves the efficiency of the system, ensures the comfort and health of occupants, and can even save on energy costs in the long run.

As an expert, I highly recommend following building codes and best practices when it comes to sealing and insulating ducts.

Candice Fedak
Candice Fedak

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