If you’ve installed a new chimney flue liner, the next step is to connect it securely at the top to either your existing chimney pot or a rain cowl. Properly joining the liner to the pot or cowl is crucial to prevent leaks and ensure proper draught. 

In this guide, we’ll go through the steps for three standard methods DIYers use to connect their chimney liner at the termination point:

  1. Hanging cowl
  2. Mortar inside chimney pot
  3. Direct connection to existing pot 

Choosing which approach depends on whether you’ll install insulation around the liner, like vermiculite, or leave an air gap. Let’s examine how each method works. 

Method 1: Hanging cowl

The hanging cowl method suspends the flue liner from the cowl itself. It’s best suited for situations where insulation around the liner will not be installed. 

A hanging cowl kit typically contains:

  • Rain cowl
  • Two jubilee clamps of different sizes
  • Hanger straps

Here’s how it works:

The cowl has a tapered male end that inserts into the female end of the liner. If you’re using our DURAFLUE liner, either end will work. The smaller jubilee clamp fits around this joint, clamping the liner to the cowl’s outlet tube. The larger jubilee clamp then wraps around the straps encircling the chimney pot, suspending the liner and cowl down from the pot. 

The hanging cowl approach has several advantages:

  • It’s speedy and straightforward to install—no need to remove and refit the pot or mix mortar. 
  • You can often use your existing chimney pot as long as the liner fits through it. 

However, it may not be suitable if your chimney pot has an ornamental shape or a very narrow opening. It’s also not ideal for large-diameter liners – additional support may be needed. 

Tips for assessing if your existing chimney pot will work:

  • Check that the outlet opening is large enough for the liner to pass through. 
  • Consider aesthetics – a tall or decorative pot may look strange with the cowl suspended underneath. 

You can cut down an unsuitable pot to simplify installation. But take safety precautions—chimney pots are extremely heavy! Use proper equipment, like an angle grinder with a diamond-tipped disc, and work from a supported platform rather than a ladder. 

Attaching the hanging cowl:

  1. Fit the smaller jubilee clamp around the joint where the liner inserts into the cowl outlet tube. 
  2. Tighten it firmly with a screwdriver. To tighten correctly, the “bolt” part must be flat against the liner. 
  3. Position the cowl and liner in place, lowering into the pot opening. 
  4. Fit the larger jubilee clamp around the strap encircling the pot. 
  5. Tighten securely. This suspends the liner and cowl from the pot rim. 

In some cases, it's best to fit the cowl last. For example, if the bottom of the liner is already fixed with a register plate, Here’s how:

  1. Leave enough liner protruding from the top to fit the small clamp over the cowl outlet. 
  2. Press down firmly on the cowl so the liner compresses. This allows the cowl to reach the pot rim. 
  3. Fit the more oversized clamp around the pot straps while maintaining downward pressure. 
  4. Carefully release pressure while ensuring the cowl remains in position. 

The liner will be well-supported in most chimneys – tight bends and the walls provide friction. But for substantial diameter liners in wide flues, use roofing screws with washers instead of the clamp for added support. 

Method 2: Mortar inside chimney pot 

This method involves using mortar to seal the gap between the liner and the inside of the chimney pot. It’s the preferred approach when installing insulation like vermiculite granules. 

You’ll need:

  • Top plate – circular plate with a hole for the liner to pass through 
  • Top clamp – seals liner to the top plate 
  • Top sleeve (optional but recommended) – inserts inside the liner for the clamp to grip
  • Mortar mix 

Steps:

  1. Remove existing chimney pot using care – they are cumbersome! 
  2. Lower the liner through the top plate’s opening. 
  3. Position the top plate on the chimney crown. 
  4. Slide the top sleeve inside the liner if using one. 
  5. Fit the top clamp over the liner and sleeve (or liner alone) and tighten firmly. This seals the liner to the top plate. 
  6. If insulating with vermiculite, pour granules into the gap between the liner and chimney walls and let them cascade to the bottom. 
  7. Fill the gap between the liner and pot with mortar. Angle it at 45 degrees, allowing soot to run into the liner rather than build up. 
  8. Allow the mortar to cure fully as per the manufacturer’s instructions. 
  9. Refit the chimney pot. 
  10. Flaunch the gaps between the pot and bricks with new mortar. 
  11. Install a rain cowl to prevent water ingress. 

If using vermiculite insulation, budget around one bag per metre of chimney depth. Purchase a bit extra to ensure the gap is filled completely. 

Method 3: Direct connection to existing pot 

If you won’t be installing insulation, a simple mortar seal between the liner and pot is all that’s needed:

  1. Using an angle grinder, hacksaw, or snips, cut the liner 1-2cm above the top of the chimney pot. This provides an overlap for the mortar to adhere to the pot rim. 
  2. Pack the gap between the liner and pot with scrunched-up chicken wire, around 15cm down. This prevents mortar from dropping. 
  3. Mix the mortar. Begin with a dryish consistency, then add water gradually until you achieve an easily trowelable texture. 
  4. Generously fill the gap around the liner with mortar. 
  5. Smooth and slope at 45 degrees. 
  6. Allow a total 24–48 hours to cure completely before using your stove. 
  7. Fit a rain cowl. 

Take your time fitting the liner and cowl or pot connection. Rushing can lead to leaks or other issues. If you are uncertain about your DIY skills, consider hiring a professional installer. But when done correctly, you can achieve a secure, weathertight seal that will last for years! 

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