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AmargosaJim, Handyman
Category: Home Improvement
Satisfied Customers: 16
Experience:  25 years carpentry and electrical, 23 year appliance repair, 18 years schooled Refrigeration, MORE
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I am getting a gas smell from furnace when it is running

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My gas furnace emits a gas smell. It's a Carrier, six years old. A technician found no CO problems. The smell is unpleasant though. Any suggestions? It's mostly when the furnace is running.

The furnace is suppose to have the burner that is burning the gas isolated from the living area. There should be a flue pipe out through the roof or in some cases a wall to the outside. The gas, prior to being burnt is piped in to the mostly sealed area where your control unit and the burner is. You are either getting gas from a leak prior to the burner (which is a fire or explosion hazard) or unburned gas from the heating chamber is escaping into your living area (which can cause carbon monoxide inhalation which displaces oxygen in your blood and can cause head aches up to death). This is a serious problem and you need to correct it or quit using the furnace.

I have seen leaks in the pilot supply cause a pretty bad smell. If you use a water and dish soap solution, something at about 8 to 1 to 4 to 1, water to soap, and use a paper towel or paint brush to apply it to all the piping on and to the furnace. Look for a leak to be blowing bubbles. It is low pressure so it won't be like a leak in a car tire with a long bubble stream, it will be a slow inflating bubble so you have to move slow and look carefully.

Another cause of the gas smell is a plenum that has a leak into it from the fire chamber. The fire burns and as the heat rises up and out the flue it goes through a baffle system. The inside is the fire and the outside the fan pulls air from your house over it and then pushes it through to the duct where it is sent throughout your house. If there is hole or crack in that baffle or the area where the burner is, it will pick up some of the exhaust from the flame and send it into your house. There could also be a leak in your flue pipe as it leaves the furnace, you can check this by looking at the exhaust piping. On top of the roof there should be a cap on the pipe like a hat. If this has been removed there could be a back breeze caused by wind outside.

As you can see there are many causes that are possible. They may be even more if I knew more of the facts. If you can't find the problem it is well worth finding a technician that knows what they are doing to fix it. You could tell me if you have natural gas or propane, in a mobile home or stick built home or any information about if it was a professional install etc.. I might be able to narrow it down.

Hope I have helped.. Feel free to ask for more details or give me information so that I can narrow it down. Remember!!! This could be a dangerous situation.

Customer: replied 9 years ago.

Thanks. Here's some additional information. Natural gas furnace located inside the house. Six years old, professionally installed. Regular 2500 sq ft house. Also, central AC.

Is the furnace behind a door or panel in one of your rooms and is the A/C using the same space and the same blower? Check for leaks with the soap and look at the flue outside to see if it is covered with the storm cap and make sure it is not plugged or covered with tree limbs or a bag or something that blew over it. If you can see the flame on the burner, what color is it burning? If the flame is not visible, like you have to open a door to see it, open the door and put a piece of transparent glass or plastic over the hole so that air can't get in through the hole and observe the flame color.. if it is red to orange, how close to the burner does the color go before it turns blue or yellow? Be careful to test for the leaks before you open any access to the flame.

Ok.. I will wait for your reply.

Customer: replied 9 years ago.

Furnace is in a closet next to family room and A/C condenser is using same space. A/C compressor is outside. Using the same blower in the closet. Furnace is electronic ignition (no pilot). Flame color is blue. No leaks I can find. Smell is more of combusted gas as opposed to unburned, or so it seems. Thanks in advance.

So that narrows it down to a leak in the plenum to burned gas, or your flue is backing up. A carbon monoxide meter should be used to check the vents to see if the recycled air is being contaminated. If your flue is backing up it could be sucked into your return air, the air inlet of the furnace. Since the flame is blue the smell is not unburned fuel. The flue is the only one you can check without special equipment. Did the problem start this winter?

Did you have any other work done to your house any time before this problem started?

Have you had windy weather that is not normal for where you live? (grabbing at straws a little)

Sounds like exhaust, just have to figure out where it is coming from. Are there places in the house where it smells the strongest or not at all?

And as I forget since I live in the middle of nowhere out here, the gas company and sometimes the fire department will check out these dangerous leaks for free.

Customer: replied 9 years ago.

This is the first winter I can remember the smell. The gas company is coming Monday. Do they check exhaust? Weather normal but there were some high winds in the winter. Vent pipes seem OK on the roof. No home improvement projects recently.


They do check out the exhaust. It is good that they are coming and can check it for you. It could be that we will never find the cause without actually doing some tests and inspecting the flue pipe above the furnace etc. One more thing is the furnace cover. Is it on tight and all the pieces there? It is important to isolate the return air from the top of the furnace where the flue pipe is. Sometimes the return air can have a leak in the furnace area an draw exhaust from the flue.

Good luck Monday if you don't find it this weekend.

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