Blocking Off Ductwork: A Bedroom Renovation Guide

Blocking ductwork in a bedroom can be done for a variety of reasons, such as reducing airflow to the room, preventing drafts, odours, or noise, or improving the room's aesthetics. However, it's important to note that blocking HVAC vents can have adverse effects on the system, including increased pressure, reduced efficiency, moisture buildup, and reduced lifespan of critical components. Here are some ways to block off ductwork in a bedroom:

- Using a Sheet Magnet: Measure the height and length of the vent and purchase a sheet magnet that is at least as big. Cut the sheet magnet to size and place it over the vent.

- Blocking a Vent with Wood: Unscrew the vent plate and measure the height and length of the grates. Cut a piece of plywood to size and tape it over the grates on the backside of the vent plate. Screw the vent plate back over the vent opening.

- Manually Closing the Vent Grille Covers: Adjust the angle of the metal fins on the vent grille covers to reduce airflow.

- Sealing Grille Perimeters: Apply silicone caulk around the edges of the grille to seal any gaps.

- Using Dropped Ceilings: Install a secondary ceiling below the main ceiling to cover ductwork while still allowing access for maintenance.

- Decorative Coverings: Use decorative panels, mouldings, or false beams to cover exposed ducts and turn them into design features.

How to Block Off Ductwork from a Bedroom

Use sheet metal and mastic to seal ductwork

Sheet metal and mastic are two of the most effective ways to seal ductwork. Here is a step-by-step guide on how to use them:

Step 1: Clean the Ductwork

Before applying any sealing products, it is important to ensure that the ductwork is clean and dry. Use a dry cloth to wipe down the ducts, paying special attention to the seams and joints. This will help ensure that the mastic adheres properly to the surface.

Step 2: Secure Connections with Screws

Sheet metal ducts should be properly secured before sealing. Fit the pieces together by sliding the wider pipe over the narrower connecting collars. Use screws to secure the connections and ensure that all joints are tight and secure.

Step 3: Seal with Mastic

Mastic is a thick, gooey, non-hardening substance used to seal duct seams. It can be applied with a paintbrush, putty knife, or even your fingers (if wearing gloves). Spread the mastic over all seams and joints, including those in the elbows and where the elbow and straight pieces meet. For added strength, cover any gaps wider than 1/8 inch with fiberglass mesh tape before applying the mastic.

Step 4: Allow Mastic to Dry

Follow the manufacturer's instructions for drying time. Mastic typically takes several hours to dry, and it is important to ensure it is fully dry before handling or covering the ducts.

Step 5: Inspect and Maintain

Once the mastic is dry, inspect the ductwork to ensure that all seams and joints are properly sealed. Over time, it may be necessary to reapply mastic to maintain an airtight seal. Regularly inspect and maintain your ductwork to ensure optimal performance.

Using sheet metal and mastic to seal ductwork is a straightforward process, but it requires careful preparation and attention to detail. By following these steps, you can effectively seal your ductwork, improving energy efficiency and reducing the risk of air leaks.

Seal ductwork with duct tape

While duct tape is great for many purposes, sealing ductwork is not one of them. The name is misleading, and although it is a strong binding agent, it is not suitable for sealing ducts.

If you want to seal ductwork with tape, you should use HVAC duct sealing tape, also known as aluminium foil tape. This can be found in hardware stores and comes on a roll. However, this method is less effective than other duct-sealing methods and may not be long-lasting. If you do use this type of tape, opt for foil tape, butyl tape, or duct sealing tape marked with the UL logo, which indicates it is suitable for residential use.

If you are sealing ducts that often get dirty or oily, duct sealing tape is likely to fail. In this case, you could use duct mastic sealant, a gooey substance that hardens after application. Water-based duct mastic sealant is the best option for easy cleanup, and it will last a long time. You can apply it with a paintbrush or a caulk gun.

If you want to seal ductwork in your bedroom, it is important to consider the size of the gaps you are trying to seal. For large gaps, you may need to combine duct tape or duct mastic with another product, such as fiberglass mesh tape.

Block the vent with a piece of furniture

If you want to block off ductwork from your bedroom, one option is to block the vent with a piece of furniture. This method is simple and doesn't require any tools or modifications to your ductwork. However, it's important to note that blocking HVAC vents can have adverse effects on your system. It can increase airflow pressure elsewhere, reduce system efficiency, cause moisture buildup and mould, and shorten the lifespan of critical components. Therefore, it is recommended to not block more than a quarter to a third of your HVAC vents at once.

To block a vent with furniture, simply place a piece of furniture in front of the vent opening. Make sure the furniture is large enough to completely cover the vent and prevent airflow into the room. You can use any type of furniture that fits the space and your aesthetic preferences, such as a bookshelf, cabinet, or dresser. If you don't have a suitable piece of furniture, you may need to purchase or build something that fits the space.

When placing the furniture, be careful not to damage the vent or any surrounding structures. Ensure that the furniture is stable and secure, especially if it's in an area where it could be knocked over or bumped into. Additionally, keep in mind that blocking the vent will reduce airflow to the room, so make sure there is adequate ventilation from other sources to maintain a comfortable environment.

If you decide to unblock the vent in the future, simply move the piece of furniture away from the vent opening. This method provides a quick and easy solution to blocking off ductwork without making any permanent modifications to your home. However, keep in mind the potential impact on your HVAC system and consider consulting with a professional HVAC contractor if you have any concerns.

Seal grille perimeters with silicone caulk

Sealing the grille perimeter with silicone caulk is a great way to block off ductwork from a bedroom. This method ensures that the vent is properly sealed, reducing airflow to a more suitable level. Here is a step-by-step guide to help you seal the grille perimeter effectively:

Firstly, turn off the HVAC system. This is an important safety precaution as it prevents any potential hazards while you work near the ductwork. Once the system is off, carefully feel around the vent grille for any cold drafts. This step is crucial as it helps identify any air leaks that may be present.

If you detect drafts, it's time to unscrew the cover of the vent grille. Use the appropriate tools to remove the screws and lift the cover from its mounting. With the cover removed, take a close look at the edges of the grille. This is where you will apply the silicone caulk to create an effective seal.

For the next step, you'll need a tube of silicone caulk. Ensure you have enough caulk to cover the entire perimeter of the grille. Apply a bead of caulk that is approximately 1/8-inch thick along the edges of the grille. Work carefully to ensure the caulk forms a continuous seal around the grille.

Once you've applied the caulk, it's time to screw the cover back in place. Make sure it is secure and fits snugly. After this, all you need to do is wait for the sealant to dry. Depending on the type of caulk used, it may take around 12 hours or more for it to completely cure.

By following these steps, you can effectively seal grille perimeters with silicone caulk, reducing airflow into the bedroom. Remember, it is important not to block more than a quarter to a third of your HVAC vents at once, as it can have adverse effects on the system and reduce its efficiency.

Partially close vents to control airflow

While it is not recommended to close vents completely, you can increase energy savings by partially closing one or two outlets in your home that are farthest away from your furnace. Partially closing vents still allows air to flow properly through the HVAC system, preventing overheating and added pressure to the ductwork.

You can also use dampers to "tune" a slightly unbalanced system by blocking 10-20% of the airflow in one or two vents. If you don't have dampers, you can cut blocks of insulation and place them in the vents. Cut the blocks in half and place them in the registers, then cut them in half again if that is still too warm.

If you want to control airflow, you can also take round dampers and put them in the supply lines. You will need to isolate them to figure out which go upstairs and downstairs. The more zoning you want to do, the more dampers you will need.

Frequently asked questions