I have a (LP) gas fireplace which I never used before for I have not lived here for long. Occasionally, a loud “bang” is heard from the fireplace or chimney. I WAG the chimney is an aluminum duct inside, and the duct is expanding and contracting thus making the noise. Anyone else experience this? And, is this the culprit?
My (not gas) chimney does this, and it’s because of the wind. I’m not sure what the offending part is, but it can get really annoying… and it’s been really windy recently.
When the weather was warmer, I swear there was an owl living in there too.
My wood burning fireplace also makes an occasional “bang”. I just attributed it to heat expansion of the fire box or flue. I’ve never noticed a trend.
One question … are these center-mount chimneys, mid-house, up through roof, or external side-mounted chimneys?
Mine is a center-mount.
I have heard flue dampers getting sucked up by high winds over the top of the flue and then suddenly dropped. Can make an amazing bang. So, next time see if the wind is blowing.
A center mount is obviously better insulated from the outside air than a side-mount. Even if you have a gas or oil appliance running for heat or hot water, they are more often than not escaping through a seperate flu and not adding much warmth to the adjoining flu…
So … whether your flu is tile. or metal, it tends to be a lot colder on an ouside mount, and the initial burst of heat when you light your fire, (usually with newspaper right?) can have a differential of a few hundred degrees between the surface of the flu and the warm gas you’ve just introduced. For some reason, probably chemicals in the ink, Xmas wrapping paper burns very hot and many people have had tiles crack, or even chimney fires when starting their fireplace on a cold day.
Even if you have a center mount, insulated by the house interior, save but the top few feet, you can still have a lot of cold air sitting in the flu, especially if you live in a very cold climate. Most fireplaces have a bottom damper, that is the one you reach into the fireplace to open, and these can allow the colder outside air to settle into the flu.
A possible solution for that is a top mount damper. It sits atop the flu at the top of the chimney. It is connected by a pull chain and is easily opened/closed from within. This allows the warmer house air to rise up the flu, but not escape, and so long as you are not using a lot of hot burning fuel to get the fire started you should hear no more banging.
As for the outside mount, there is not too much you can do to prevent the banging other than to be a bit more conservative when starting your fire. Introduce the heat as slowly as practicible.
The banging can mean problems, especially with tiled flues. Too much banging (expansion) and they easily crack and break. Then your troubles can involve anything from a house fire to carbon monoxide poisoning, pretty deadly and difficult to detect without a sensor. Also, a re-line for a chimney can easily cost a couple of grand that you probably don’t feel like spending.
If you know what to look for shine a strong light up from below and then down fron the roof to see how the flu looks. Be advised, few of them are straight up and down and the soot can often make cracks and breaks hard to spot.
There is probably a CERTIFIED chimney sweep in your area who will do an inspection for a decent price, usually free if it needs sweeping.
And, no, I am not a chimney sweep!
Is it on a thermostat?
Do you use if for heat?
If so, you might be hearing the initial start up. The pilot light lites the incoming gas. Usually more of a WHOOMFFF. But the extra pressure may wang your flue enough to get a bang.