You probably perform furnace maintenance. You can keep your furnace running efficiently by keeping it clean and replacing the filter. Furnace maintenance goes beyond the actual furnace unit in your home and includes the ducts and venting systems.
Sealing your outdoor furnace vent is necessary maintenance. Though not related to your furnace, a properly sealed vent can boost its furnace. Check your furnace vent annually.
In our guide, we explain why you should seal your outside furnace exhaust pipe. By the end, you’ll learn how easy it is to seal a vent at home to keep heat in and draughts and even insects out. (Learn How To Kill Roots In Pipes)
How Do You Seal A Furnace Vent Pipe?
Here you can learn why sealing your furnace vent is essential.
It is essential to seal your exterior furnace vent joints as doing this can help prevent air drafts, water leaks, and insects from gaining access to your home. Besides this, you can prevent any combustion gases from blowing back through the gaps as these contain carbon monoxide.
In addition, by blocking as many gaps as you can, your home remains more energy efficient.
Sealing your furnace vent piping outside is a simple task that requires minimal equipment and time.
To make sure your vent is sealed correctly, follow the steps below. When sealing your vent, keep in mind that the exhaust pipe sealant must be completely dry before using your furnace as it could lead to cracks and other gaps.
Overview of how to seal vent pipe:
Make sure the area is clean
Clean the area around the vent of any dirt or debris. To apply the sealant, you’ll need a clear, clean surface.
Apply sealant to the area
You can use caulking or a foam sealant to seal your vent pipe. Apply the sealant to the area according to the manufacturer’s instructions. Make sure that all gaps are filled in.
If you’re using caulking, smooth it out while wet after you apply it. If using foam sealant, trim it level to give it a more professional appearance.
Sealing your exterior furnace vent is, as you can see, a simple task many people can complete on their own.
Although this task should be long-lasting, it is always good to regularly inspect the seal for damage.
What Do You Seal A Furnace Flue Pipe With?
An exhaust pipe flue leading to an attic chimney is often used with older, less-efficient furnaces.
Because modern furnaces are so energy-efficient, much of the heat that used to be vented up a chimney is now retained and used to heat the house.
As a result, all modern energy-efficient furnaces now vent through a PVC or metal pipe that runs directly out of the side of the foundations.
These vents must be sealed to prevent air drafts, water leaks, and even insects from entering your home. (Learn How To Dissolve Wipes In Pipes)
Seal gaps up to 1/4 inch with silicone caulk; anything more extensive than that will require foam sealant.
How to Use Silicone Caulk
- With a stiff bristle brush, remove any dirt or dust from the area around the furnace vent that you will be sealing.
- Using a utility knife, cut the tip of a silicone caulk tube. Some caulk guns include built-in tube cutters on the grip that works like scissors.
- Fill the caulk gun with the caulk tube.
- As you move the tip around the seam on the furnace flue, squeeze the trigger firmly and evenly. Ensure an even, consistent bead of heat resistant RTV caulk is applied around the seam.
- Fill the gap, then smooth the silicone around the vent with your finger for aesthetic purposes.
- On your flue pipe, caulk, and tool each extra seam. Then, before turning on your furnace, let the high-temperature RTV silicone caulk cure completely.
If your furnace is older, it vents through a hard metal conduit into a chimney.
The flue slip connections slide into one other and are secured with screws. You’ll likely notice gaps around the wood blocking and insulation used to make these connections.
If these cracks are left unsealed, combustion gases could leak into your home and build up to unhealthy levels.
Because these pipes can get so hot, building codes often demand spaces left to any combustible material such as attic insulation:
- One inch of space from a metal flue.
- Two inches from masonry chimneys.
How Do You Seal A PVC Vent Pipe?
You may ask, can you duct tape a furnace exhaust flue PVC pipe to stop a leak? It would be best if you didn’t seal a furnace vent pipe with cloth duct tape; instead, you can find foil tape from manufacturers such as 3M, who make a high-temperature tape rated to 600 degrees.
How do I keep cold air from coming into my exhaust fan?
The flue fan should have an internal flapper damper to restrict cold air, but it frequently fits poorly and air leaks through. If you wish to halt cold air, you need a fantastic damper or double damper at the exhaust hood where air leaves your home.
How do you seal a flexible air duct?
Mastic is used to seal flexible ducts, and you should use UL-181–rated duct mastic and tie all junctions in place with tie wraps. (Read Replace Rubber Seal Around Shower Glass Guide)
Can you duct tape a dryer vent?
Foil tape should seal dryer vents since it can withstand the high temperatures seen during machine use.
Other tapes, like duct tape, are susceptible to breakdown in intense heat, and non-foil tape can also catch fire.
Can I Spray Foam Around Furnace Vent?
Depending on gap size, you may need to use spray foam insulation rather than silicone to seal around large gaps around any hole around the wood frame holding the flue or exhaust in position.
Using Foam Sealant
- Using a stiff bristle brush, brush the area to be sealed. This will remove any dirt or other loose particles that may be preventing the foam from adhering to the vent.
- The cap of a can of spray foam sealant should be removed. A plastic zip tie is commonly used to keep the cap in place. When the cap is removed, a dispensing trigger appears.
- As you move around the sides of the vent, pull the trigger, and let the foam sealant completely cover the gap. As the foam plugs the area, it will spread out of the gap.
- When the foam sealant has completely cured, use a utility knife to trim it. Cut the foam as near the edge of the vent as possible, then sand it smooth with 220-grit sandpaper once it has cured.