08/04/2013
How do you know if you do have a crack in the heat exchanger of you gas furnace? Can you get carbon dioxide into your home from your furnace?
If you have a 80+ or 90+ gas furnace you can not get carbon Dioxide from a cracked heat exchanger!!
To tell if you have a 80+ or 90+ gas furnace you have to check the following. Have someone turn your thermostat to heat and turn it above the room temp. With you standing next to the gas furnace if you hear a small motor turn on before the main blower you have a 80+ or 90+ furnace. If you have a flue pipe coming out of the furnace which is metal, you have a 80+ furnace. If there are one or two plastic pipes coming out of your furnace, you have a 90+ furnace.
If you have a serviceman in your home and he puts a camera into your furnace and shows you a crack, in all most every case he is wrong. Many companies use this to scare people into get a new furnace. The area inside of your furnace has a lot of area, for him to find a crack, it doesn't happen
So how can you know if there is a crack? A tester is put into the flue pipe which test the carbon dioxide in the flue gas. The little motor that sucks the flue gas out of your furnace and puts it outside does not change speed if there is a crack. It pulls air though the burners along with the lite gas. If air is being pulled in though a crack in the heat exchanger, it is not pulled though the burners.
This will cause the burners not to have enough air for the gas to burn right. The flame will start to turn yellow and carbon dioxide will be produced. This is what the tester will pick up and measure. If it is too high the furnace needs replacement.
If the furnace is still working there is no hurray to replace it. If the crack becomes big enough, the heat from the flames will not be pulled into the heat exchanger. Above your burners there are senors which have a manual reset that will open. This will turn your burners off and the furnace will not heat. On some models the blower in the furnace will run all the time and there will be not heat. Other models do not.
So don't be taken by the type of serviceman with a camera and no tester in the flue. Call another company.
The best way to get a good company is to check with the Better Business Bureau. You can find them on line at bbb.org and it is free.
Also report to them anyone who just uses a camera.