Metal HVAC Pipes
Do It Yourself Roof Repair: HVAC Pipes

Another fairly common pipe leak is around metal HVAC flues.  These pipes are usually 4 to 6 inches in diameter and they exhaust fumes from heating systems or hot water heaters to the outside of your home (fig. 1) There are two metal parts to consider besides the pipe itself and the cap.  As the pipe exits the roof there will be a shroud that surrounds the pipe and attaches to the roof to secure it.  Shingles are then woven around it to make a water tight fit (fig. 2)

Roof Repair HVAC Pipe figure 1

Do It Yourself Roof Repair HVAC Pipes: Figure 1

 

Roof Repair HVAC Pipe figure 2

Do It Yourself Roof Repair HVAC Pipes: Figure 2

 

Next, there is a ring that looks like a small Frisbee with a hole in the middle that slides down over the pipe and rests on top of the shroud. The topside of this ring should always be caulked to the pipe so that water cannot enter here and then through the top of the shroud beneath it eventually entering the structure itself (fig. 3).

 Roof Repair HVAC Pipe figure 3

Do It Yourself Roof Repair HVAC Pipes: Figure 3

 

Then the cap is secured on top of the pipe. I have never known this part to be a cause of concern.  HVAC leaks are usually because defective or no caulking was used to seal the joint between the pipe and the Frisbee looking metal ring (fig.4) . I use a commercial grade tripolymer clear caulk for this that you may purchase from me for $8.00 a tube. 

Roof Repair HVAC Pipe figure 4

Do It Yourself Roof Repair HVAC Pipes: Figure 4

 

If the base of the shroud has caulking around it water may be able to penetrate it also. It should be removed if possible and recaulked as well (figs. 5 and 6).  If the vent continues to leak it may be because the water is traveling off the side of the shroud instead of flowing down and off of it onto the shingles beneath. This may be remedied by lifting up the shingles a little on each side and sealing vertically between the metal and the underside of the shingles as high as can be reached with the caulking gun. It would be good to put a dab of caulking on any exposed nail heads as well.

Roof Repair HVAC Pipe figure 5

Do It Yourself Roof Repair HVAC Pipes: Figure 5

Roof Repair HVAC Pipe figure 6

Do It Yourself Roof Repair HVAC Pipes: Figure 6


Occasionally, the shroud will be installed incorrectly and should be redone (fig. 7). 

Roof Repair HVAC Pipe figure 7

Do It Yourself Roof Repair HVAC Pipes: Figure 7

 

The flat part of the metal that lays on the roof should be covered with shingles across the upper half and exposed across the lower portion to allow water to run off properly (fig. 8).

 

 Roof Repair HVAC Pipe figure 8

Do It Yourself Roof Repair HVAC Pipes: Figure 8