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Cold North Wind Extinguishes Gas Insert

Q: I purchased two (2) direct vent fireplace inserts for my house during our renovation project. The installers have not been able to help me with this problem, and I would appreciate your assistance.

Whenever the wind is blowing hard (particularly, it seems, a cold north wind) one of the inserts simply does not work. With some difficulty I can light the pilot, but inevitably the flame (and the pilot) are soon extinguished. Last year I learned that if I removed the glass piece from the front of the fireplace, it was quite easy to light the pilot -- presumably because the flame then had access to room air. The fireplace is installed on the ground floor of a two-story-with-attic home with the appropriate liner and chimney cap. However, I get the sense that there is not sufficient air flow through the fireplace insert, and the flame extinguishes itself when the oxygen is exhausted. It is as if the wind might be blowing the exhaust air back down the chimney. When a good flame does get established, the unit works very well.

Last evening I was able to light the pilot, but as soon as the main flame ignited, it flared briefly and then extinguished itself and the pilot light as well. It appeared clear there was simply not enough oxygen to support the flame.

We put up with this most of last winter, and now the weather is getting cold, and we have the same problem. I can't believe that the problem has never happened before to other owners of this system. Please, can you give me some advice and/or send this to the manufacturer to see if something can be done. When the fireplace works well, it is quite beautiful and it is an important adjunct heating system for our home. But when the flame burns itself out, the fireplace is not of much use to us.

Thanks for any help you can provide. (BTW, please don't ask me to contact the installers again. They have not been able to help. What I need is somebody with some experience with the problem, and then perhaps I can suggest to them a solution.)

John W. Aldis, M.D.

Sweepy A: Hi Dr. John,

Thanks for the inquiry! First, let's look at how a safety pilot works. Whenever blockage, wind, or atmospheric conditions impede the flow of exhaust up the chimney, the exhaust gases build up in the fire chamber until the pilot flame is extinguished from lack of oxygen. As soon as the pilot goes out, the thermopile cools and stops generating the millivolt current that enables the flow of gas to the burner, and it goes out too. This is a safety precaution, to prevent the poisonous gases created by the fire from entering your breathing space whenever anything interferes with the flow of exhaust up your chimney. In other words, it sounds to me like your safety pilot is simply doing its job.

Your observation that the pilot and burner both stay lit when you remove the viewing window is evidence that the most likely cause of your problem is insufficient exhaust flow. When you remove the glass, the exhaust flows into the room instead of filling the fire chamber, and room air flows into the fire chamber to replace it, so the safety pilot and burner stay lit. Removing the glass is not a good solution, however, because odorless, colorless exhaust gases are poisoning your breathing space whenever the glass is not in place.

If a solution is to be found, it will involve trying to determine what is inhibiting the flow of exhaust gases up your chimney. For an overview and some background information, you might want to pause here and read the article titled "Draft problems; causes & solutions".

If this problem only occurs when you've just lit the pilot, it is most likely because the cold, high-density air in the exhaust liner is creating a "plug" which prevents the free flow of exhaust up the flue. This problem is often worse in taller chimneys, because the plug is very tall and very heavy. If this were a wood-burning fireplace, you could "prime" the flue by burning loose balls of newspaper in the fireplace until the rising heat pushed the cold air plug out of the chimney. In the case of a gas fireplace insert, priming the flue in this manner isn't practical, so the cold air plug situation should be avoided. Often, all it takes is to simply leave the pilot buring all the time, using the heat from the pilot exhaust to keep the flue warm and the airflow moving upward. Burning the pilot 24/7 costs just a few dollars per month.

If the safety pilot keeps going out even when the exhaust flue is hot, the problem could be downdrafting or crossdrafting. Some chimneys are more easily victimized by wind and atmospheric conditions than others, and in your case, it sounds like you might be getting extreme pressurization at the top of this particular chimney when the wind blows from the North, which forces the exhaust to back up into the fire chamber of the insert until it triggers the safety pilot. If this is the case, your problem will be how to stop the wind-induced pressurization.

Direct vent gas insert systems have two liners running side-by-side up the flue; one for combustion air intake, and one for exhaust. At the top of the chimney, a co-axial converter box is used to allow the installation of a single co-axial rain cap. Here's something you might try; replace the standard co-axial cap with a high-wind cap. These have shaped panels around the perimeter to break up the wind and minimize draft interference.

I've given you a couple of ideas to try, but can't guarantee they will work. The sad fact is, all chimneys cannot be made to function in all situations: if keeping the flue warm doesn't work, and the high-wind cap doesn't work either, you might have to resign yourself to the fact that there will be times when this particular insert cannot be used.

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