# Is it a problem if rain gets into your furnace?

**URL:** <https://boards.straightdope.com/t/is-it-a-problem-if-rain-gets-into-your-furnace/38494>\
**Category:** Factual Questions\
**Created:** [October 26, 2000, 9:12pm UTC](https://boards.straightdope.com/t/is-it-a-problem-if-rain-gets-into-your-furnace/38494 "2000-10-26T21:12:29Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![annalamerino](https://avatars.discourse-cdn.com/v4/letter/a/b3f665/32.png) [@annalamerino](https://boards.straightdope.com/u/annalamerino)\
**Post date:** [October 26, 2000, 9:12pm UTC](https://boards.straightdope.com/t/is-it-a-problem-if-rain-gets-into-your-furnace/38494/1 "2000-10-26T21:12:29Z")

</div>

It’s raining right now and I can hear the metalic pings inside the furnace. I know there’s some sort of exhaust pipe for the gas residue to escape, and it has a mesh on top, but doesn’t it seem wrong to have water come in?  
Or is that just what happens.

---

<div class="post-metadata">

**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\
**Post date:** [October 26, 2000, 9:49pm UTC](https://boards.straightdope.com/t/is-it-a-problem-if-rain-gets-into-your-furnace/38494/2 "2000-10-26T21:49:25Z")

</div>

probally isn’t the best for it as it will help corrode the furnace esp. if it is not running. most chimey’s have a cap on top that will prevent this.

---

<div class="post-metadata">

**Author:** ![Skelji](https://avatars.discourse-cdn.com/v4/letter/s/b38774/32.png) [@Skelji](https://boards.straightdope.com/u/Skelji)\
**Post date:** [October 26, 2000, 10:13pm UTC](https://boards.straightdope.com/t/is-it-a-problem-if-rain-gets-into-your-furnace/38494/3 "2000-10-26T22:13:03Z")

</div>

**Any** chimney top or flue vent should have a raised cap over it to prevent water from entering. There’s usually about a 3 inch or more clearance between the top of the vent, and the pitched cap over it, with mesh around the opening to keep animals out.

Water entering a chimney is very bad - over time, either mortar will work it’s way loose, or a metal chimney stack will corrode. In both cases, flue gases and carbon monoxide can enter your living space.

Water entering the flue stack for a gas furnace or water heater will corrode the unit itself, specifically the heat exchanger.

Better get it checked out.

---

<div class="post-metadata">

**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\
**Post date:** [October 27, 2000, 2:18am UTC](https://boards.straightdope.com/t/is-it-a-problem-if-rain-gets-into-your-furnace/38494/4 "2000-10-27T02:18:47Z")

</div>

Are you certain that you are not hearing the sound of water hitting the flue pipe? Sometimes it sounds pretty loud, esp. during hail.

---

<div class="post-metadata">

**Author:** ![system\_hoser](https://avatars.discourse-cdn.com/v4/letter/s/a9adbd/32.png) [@system\_hoser](https://boards.straightdope.com/u/system_hoser)\
**Post date:** [October 27, 2000, 2:23am UTC](https://boards.straightdope.com/t/is-it-a-problem-if-rain-gets-into-your-furnace/38494/5 "2000-10-27T02:23:53Z")

</div>

A friend of mine was hearing a lot of loud noise coming from her furnace about a month ago. She had it serviced, and the cause of the noise and malfunction turned out to be a bat!