How to Seal Double Wall Flue Pipe on Metal Roofing

A double wall flue pipe or also known as a double walled structure of a type B gas vent is an extra safety precaution for the ventilation of gas appliances such as boilers, water heaters and furnace in your home. It require the minimum clearance of the combustibles by serving insulation which will avoid the double wall flue pipe to experience condensation that will obviously lead towards rusting and may cause serious leakage. Although a double wall flue pipe does not require high degree of clearance, it still necessitates a careful planning and expert installation.

Metal roofing does not pose the problems shingles roofing does especially when there is a chance of leakage due to the shingles left un-arranged. In order to seal a double wall flue pipe on metal roofing, firstly you would need to review the venting chart that will be provided together with the appliance by the manufacturer. It is vital to study the chart as to plan the layout of the flue pipe. Based on the specifications of the model appliances, there will be specifications with special instructions to be followed about the necessary length allowable for the flue pipe.

Next, you will be required to measure the vent connection from the appliance to the vent section that will actually penetrate the roof. You will need to actually need to take the measurement of the route that the pipe will literally be fixed upon.  Do make sure the measurement are checked and is accurate with separate measurement with each change of direction.

After that, draw a diagram of the route taken by the vent pipe in comparing your measurement and considering the standard section lengths of the double wall flue pipe vent. There are a few standard lengths when you are working with type B vent which are 18 inches, 2 ft. 3 ft. and 5 ft. it is inadvisable to cut the pipe length in the field based on the fitting of the vent. The diagram can be used as assistance to fit the sections of pipe together with one end sliding into another pipe and the other end of the same pipe piece having another pipe to slid into it.

Attach the appliance with a sheet metal screw and then lock the flue pipe together with a twist-lock system or a locking band. Check on the horizontal runs before installing the hangers onto the roof and make sure water proof sealant is used to cover up the additional hole where the double wall flue pipe runs to avoid leakage. Plastic sheets or thick tarp can be measured to fully cover the hole and surround the vent. Then, metal sheets should be nailed on the covering to secure the sealant in place.

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