# Rain water entering boiler flue. Problem? **URL:** \ **Category:** Factual Questions\ **Created:** [July 16, 2009, 7:15pm UTC](https://boards.straightdope.com/t/rain-water-entering-boiler-flue-problem/503252 "2009-07-16T19:15:16Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Busy\_Scissors](https://avatars.discourse-cdn.com/v4/letter/b/d78d45/32.png) [@Busy\_Scissors](https://boards.straightdope.com/u/Busy_Scissors)\ **Post date:** [July 16, 2009, 7:15pm UTC](https://boards.straightdope.com/t/rain-water-entering-boiler-flue-problem/503252/1 "2009-07-16T19:15:16Z")
It is tipping it down in Edinburgh at the moment. I can hear rain water hitting the inside of the flue pipe of my boiler. Is this a problem? It must be getting blown into the flue - my boiler is a modern combi one. Any central heating guys able to advise on this? Can’t think of much I can do about it, mind. It’s currently off and I can make sure it stays off. ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [July 16, 2009, 9:21pm UTC](https://boards.straightdope.com/t/rain-water-entering-boiler-flue-problem/503252/2 "2009-07-16T21:21:57Z")
> [@Busy\_Scissors](#): > > It is tipping it down in Edinburgh at the moment. I can hear rain water hitting the inside of the flue pipe of my boiler. Is this a problem? It must be getting blown into the flue - my boiler is a modern combi one. Any central heating guys able to advise on this? > > Can’t think of much I can do about it, mind. It’s currently off and I can make sure it stays off. Is it PVC or metal? If its PVC don’t worry about it. It’s a condensing boiler and it will run to a drain. Or, if it’s PVC you can put a 90 elbow on it, and a “street 45” on the 90. That will turn it slightly away from rain without turning it directly onto the roof. (flue gas is highly acidic) If it’s a metal flue, than the top of the flue should have a “storm cap” on top of the flue, with a “storm collar” below the cap and above the roof. The **storm cap** keeps water from getting **into** the flue, and then making it’s way into the burner chamber/ heat exchanger/ The **storm collar** keeps water from running down the **exterior** of the flue pipe and them into your attic through the roof penetration. If it’s raining right now and you have no storm cap don’t fret. It’s not a good thing but one rainstorm will do little or no damage. Over the longer term, however, a storm cap is needed, and you should get one soon. ---
**Author:** ![Busy\_Scissors](https://avatars.discourse-cdn.com/v4/letter/b/d78d45/32.png) [@Busy\_Scissors](https://boards.straightdope.com/u/Busy_Scissors)\ **Post date:** [July 16, 2009, 9:38pm UTC](https://boards.straightdope.com/t/rain-water-entering-boiler-flue-problem/503252/3 "2009-07-16T21:38:39Z")
thks **raindog** , it’s a pvc pipe straight out to the wall. I live in a flat, so the boiler is just right there against the outside wall - pipe can’t be more than 1m long. Anyhow, I’ll take yr advice and not worry about it 🙂 ---
**Author:** ![raindog](https://avatars.discourse-cdn.com/v4/letter/r/2bfe46/32.png) [@raindog](https://boards.straightdope.com/u/raindog)\ **Post date:** [July 17, 2009, 2:12pm UTC](https://boards.straightdope.com/t/rain-water-entering-boiler-flue-problem/503252/4 "2009-07-17T14:12:27Z")
> [@Busy\_Scissors](#): > > thks **raindog** , it’s a pvc pipe straight out to the wall. I live in a flat, so the boiler is just right there against the outside wall - pipe can’t be more than 1m long. Anyhow, I’ll take yr advice and not worry about it 🙂 One other thing… If there is only 1 PVC pipe than don’t worry. (because that one pipe is an exhaust) If there are _2_ pipes…than one is a fresh air intake, and it’s not a good thing to have water in it. The way to “test” this would be to fire the boiler and the one that is producing hot flue gases is the exhaust----and that is the one that won’t mind some rain water.