# Why is the furnace howling? **URL:** \ **Category:** Factual Questions\ **Created:** [February 10, 2021, 6:29pm UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623 "2021-02-10T18:29:34Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [February 10, 2021, 6:29pm UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/1 "2021-02-10T18:29:34Z")
Our propane tank was filled yesterday. Since then, the furnace occasionally howls when it starts up. I called the propane company, but they don’t know why. My hypothesis is that there was moisture in the fuel that was added. Since it’s in the twenties outside, I hypothesise that the moisture is freezing in the line and causing a restriction as it enters the furnace causing the furnace to howl. Once the furnace has kicked on and the contaminated fuel is pushed through, the noise stops. The woman at the propane company said that if that was the case, all of their customers would be affected. (Maybe they are, but no one else has called?) 1. Is my hypothesis reasonable? 2. Does anyone have a factual answer as to why the furnace is howling? ---
**Author:** ![Folly](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/folly/32/3219_2.png) [@Folly](https://boards.straightdope.com/u/Folly)\ **Post date:** [February 10, 2021, 7:18pm UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/2 "2021-02-10T19:18:40Z")
Coming from the propane tank regulator by any chance? ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [February 10, 2021, 7:27pm UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/3 "2021-02-10T19:27:52Z")
It’s coming from the furnace, inside the house. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [February 10, 2021, 7:35pm UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/4 "2021-02-10T19:35:09Z")
Perhaps in this temperature range the chimney is creating the sound in one of several pyrophonic modes. A [Rijke tube](https://en.wikipedia.org/wiki/Rijke_tube) is an example of this. There are a variety of other [pyrophone](https://en.wikipedia.org/wiki/Pyrophone) sound pipes. They can be as simple as an open flame in a pipe with the proper configuration. **Usually this would require some kind of additional air inlet, and that might be an indication of a leak in the chimney.** ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [February 10, 2021, 7:44pm UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/5 "2021-02-10T19:44:10Z")
When howling pour a pot of warm water over the tank. If it goes away then it most likely is water/moisture. If so they can add (I think) methanol to the tank to help, even if it’s something else there is a dryer chemical they can use. ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [February 11, 2021, 1:03am UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/6 "2021-02-11T01:03:16Z")
Sometimes a clogged air filter will cause a furnace to whistle or howl. Yours might have coincidentally gotten dirty enough to howl when your tank was filled. Or, it could be, you know, a werewolf in the flue. ---
**Author:** ![TriPolar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripolar/32/3008_2.png) [@TriPolar](https://boards.straightdope.com/u/TriPolar)\ **Post date:** [February 11, 2021, 1:09am UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/7 "2021-02-11T01:09:12Z")
> [@AskNott](#): > > Or, it could be, you know, a werewolf in the flue. If that was the case it would only howl during a full moon. ---
**Author:** ![abcdefghij](https://avatars.discourse-cdn.com/v4/letter/a/43a26b/32.png) [@abcdefghij](https://boards.straightdope.com/u/abcdefghij)\ **Post date:** [February 11, 2021, 1:19am UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/8 "2021-02-11T01:19:05Z")
How is a werewolf stuck in the flue supposed to see the moon? ---
**Author:** ![Dag\_Otto](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@Dag\_Otto](https://boards.straightdope.com/u/Dag_Otto)\ **Post date:** [February 11, 2021, 1:56am UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/9 "2021-02-11T01:56:51Z")
It can happen on the solstice, but only if a Druid installed the flue. ---
**Author:** ![Dag\_Otto](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@Dag\_Otto](https://boards.straightdope.com/u/Dag_Otto)\ **Post date:** [February 11, 2021, 2:03am UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/10 "2021-02-11T02:03:07Z")
Back to the problem at hand. Does the howling start when the burner comes on, or when the fan comes on? And does the furnace have just the main fan that blows air in the house, or does it also have an induced draft fan on the flue? ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [February 11, 2021, 2:09am UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/11 "2021-02-11T02:09:39Z")
It starts when the burner comes on, not when the fan comes on. The fan only blows in the house. ---
**Author:** ![Dag\_Otto](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@Dag\_Otto](https://boards.straightdope.com/u/Dag_Otto)\ **Post date:** [February 11, 2021, 2:17am UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/12 "2021-02-11T02:17:17Z")
Any other propane appliances in the house like a water heater or rangetop? If so, can you tell if the flames on those look or sound any different? Probably won’t be able to tell on a water heater, but it may be noticable on a stove burner. First thing a technician might check is the pressure of the propane line. Regulators are usually hassle free, but maybe something caused yours to change a little bit. ---
**Author:** ![Dag\_Otto](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@Dag\_Otto](https://boards.straightdope.com/u/Dag_Otto)\ **Post date:** [February 11, 2021, 2:25am UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/13 "2021-02-11T02:25:12Z")
Oh, and liquid propane is lighter than water, so any water in the propane tank would be at the bottom. I don’t think it would cause problems even if there was water in the tank. ---
**Author:** ![Dag\_Otto](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@Dag\_Otto](https://boards.straightdope.com/u/Dag_Otto)\ **Post date:** [February 11, 2021, 2:34am UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/14 "2021-02-11T02:34:59Z")
Speaking of density, gaseous propane is heavier than air, so it will accumulate in low places. Be careful if you suspect a propane leak. As in, get the hell out of the house careful. ---
**Author:** ![Snipe70e](https://avatars.discourse-cdn.com/v4/letter/s/51bf81/32.png) [@Snipe70e](https://boards.straightdope.com/u/Snipe70e)\ **Post date:** [February 14, 2021, 10:00pm UTC](https://boards.straightdope.com/t/why-is-the-furnace-howling/932623/15 "2021-02-14T22:00:52Z")
Low 20s, I would think any water in the propane would freeze.