What efficiency of furnace do you need?
If you are you unsure of the efficiency of your furnace go take a quick look at it. If the flue pipe coming out of it is metal, it is standard efficiency. If the flue pipe is PVC, you have a high efficient furnace.
Metal or PVC Flue Pipe?
This is the most important question that you can be asked when selecting your next furnace. The flue pipe is an important part of your furnace system and is the exhaust pipe that extends from the top of your furnace and moves dangerous exhaust out of your home.
Metal flue pipes are used on standard efficiency furnaces, sometimes referred to as type B furnaces. These flue pipes will release exhaust gases through your roof. Due to the higher temperatures of your exhaust in standard efficiency furnaces (around 500 degrees Fahrenheit) a PVC flue pipe will melt and release carbon monoxide into your home. A PVC pipe should never be used on a standard efficiency unit.
PVC flue pipes are used with high efficiency units with a rating of 92% or higher. An electric fan within your furnace forces your exhaust and through the flue pipe and out the side of your home. High efficiency furnaces create condensate that contains water. This can rust a metal pipe resulting in cracks and holes in your flue pipe where exhaust can leak out, creating an extremely dangerous environment. A metal flue pipe should never be used on a high efficiency unit.
We cannot stress enough how dangerous it can be to select the incorrect flue pipe. After conducting an internal test, a PVC pipe heated to the temperature of a standard furnace completely melted and disconnected from the furnace in less than 7 minutes. With no flue pipe and nowhere for the exhaust to go, this would fill your house with carbon monoxide. Carbon monoxide is an undetectable gas. It is odorless, colorless, tasteless, and lethal. Attaching the wrong flue pipe to your furnace will create a life-or-death situation.
If you are still unsure which is correct for any reason, it is imperative that you consult a professional before proceeding to ensure the health of your family.