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Furnace and water heater chimney leaking during heavy rain

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During heavy rains water somehow is getting into vent pipe from Water Heater/Furnace (not sure if it is both on the inside and outside of pipe) and follows the pipe down to basement and leaks.

How should I go about trying to get this fixed. Should I call a Mechanical or Roofing Company or a Handyman? I am trying to prevent getting price gouged since I am a single female who does not know too much about roofing/HVAC issues.
asked in Heating System by sheilaj (130 points)
edited by darekrudy
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1 Answer

+1 vote


Hi Sheilaj,
Unfortunately, without looking at the chimney / vent pipe it is difficult to determine what causes the leak exactly (besides the rain of course). I don’t know if you have a way of safely accessing your roof / chimney area or if you could take a picture of your chimney from the ground (zoom in on its top part while still keeping good quality of the image) and forward it to me. If taking a picture of your chimney is not possible I’ll describe a few probable scenarios. 
Another unknown variable for me is chimney’s type and location. Some of the causes of leaking chimney are closely related to it. 
Masonry chimney (brick, stone, and cinder block) located on the exterior wall of the house / three chimney walls exposed, lower part hidden underground. 
Most common sources of leakage from a masonry chimney associated with a rain fall: 
  • Missing rain cap, sometimes missing chimney liner – HVAC professional for both, handyman for rain cap only
  • Missing or damaged chimney crown – handyman, mason
  • Heavily deteriorated chimney walls that allow water penetration – mason / bricklayer
  • Cracked and leaking underground section of the chimney (whenever the surrounding grounds become saturated with rain water) – waterproofing specialist, mason / bricklayer
  • Damaged / deteriorated chimney flashing at the roof penetration - roofer
You can find more about masonry chimney here: chimney crown and chimney problems
Masonry chimney inside the house / only top section exposed above the roof
  • Everything the same as under the exterior chimney
  • If it sits on the basement’s concrete floor (of course there should be proper foundation underneath) and there’s a high water table in the area, heavy rain fall could elevate that water table even higher and penetrate concrete slab around the base of your chimney. You’d need a waterproofing company to fix this problem.
Leaking metal chimney located inside the house with section protruding from the roof
  • Missing rain cap – HVAC professional or handyman
  • Corroded metal walls / holes in walls above the roof surface penetration – HVAC professional to replace corroded section
  • Damaged / deteriorated roof flashing – roofer of handyman

Leaking furnace and water heater PVC vent pipes

  • Faulty roof flashing is usually responsible for leaks – roofer / HVAC professional / handyman would be able to take care of it
Let me know if you have more questions, click “comment” or “ask related question” links underneath. For pictures click image icon in the question form field and “upload” tab or image URL to link to it if it’s already somewhere on the web.
answered by darekrudy (21,730 points)
It is a Leaking Metal Vent Pipe (no masonry chimney) inside house with section penetrating from roof. Water follows the pipe downward 2 stories through the house until it makes a turn toward Heater. House is approximately 15 years old. I believe the water is just on outside of pipe and not getting inside of the pipe. Already has a rain cap.

If the rain water penetrates on the outside of the vent pipe it would be most likely chimney  / vent pipe flashing (picture below). This could be easily verified if you have accessible attic which this vent pipe runs through. Any gaps between the vent pipe and its flashing as well as leakage stains are very easy to spot from underneath.

Double wall / B-Vent type metal chimney - flashing is a common area of water penetration

If it's a flashing problem and if it requires replacement, the top section of the chimney / vent pipe would have to be disconnected (connection is made below the roof surface) in order to perform repalcement. You might need an HVAC and a roofing contractor to perform the repair and either one of them should be able to determine what's causing this leak.