In chilly weather, using a furnace to keep warm is a smart move. There is more to what meets the eye when it comes to this toasty appliance. Understanding all the ins and outs of furnace exhaust pipes—also called exhaust flues—is important to keep your furnace functioning, and ultimately, to keep you warm during the cold months.
How Furnace Exhaust Flues Work
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A furnace burns natural gas in your home to keep you warm. A byproduct of this is carbon monoxide, which is highly toxic. Due to its toxicity, it needs to be let out of the house in a safe manner, which is what the furnace exhaust flue does. Below are the steps to a working exhaust flue:
- A furnace burns natural gas through combustion, creating heat and toxic byproducts like carbon monoxide.
- Inside the flue, which is a metal tube, is something called a damper. The damper regulates air pressure from inside the furnace and outside the house.
- The damper, or a natural draft, then helps create the draft that pulls the toxic gases through the flue and out of the house (and keeps it out of the house).
What is a Natural Draft
Most furnace systems use natural drafts to function. A natural draft is the ability of flue gases to rise up and out of the furnace exhaust flue on their own. A natural draft is created because of pressure differences in the air from outside your house and the air in the furnace system. Since the air in the furnace is way hotter than the outside air due to the combustion process, it has lower pressure. This difference in pressure, also known as the negative pressure differential, helps the exhaust fumes get pushed out of the furnace flue. If there is insufficient pressure differential, the exhaust fumes might not be pushed out of the house effectively. This along with too many elbows in the pipe, too many horizontal sections, and inadequately wide pipes can also cause exhaust flues to struggle to exit the flue.
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What Are Draft Inducers?
Typically, older furnaces use natural drafts, and newer ones feature draft inducers. Furnaces using natural drafts are less cost-efficient than those with draft inducers, the reason being that the draft speed is not enough to get exhaust gas out efficiently.
Furnaces without draft inducers cost more to run because of their low efficiency, which is why many homeowners are choosing furnaces with draft inducers. A draft inducer is a high-powered fan that is located near the heat exchanger in a furnace and helps with the faster exit of exhaust gas. It also helps clear out any leftover toxic fumes in the combustion chamber.
Where Should an Exhaust Flue Go?
The two places that exhaust flues go are either out of the roof of a house or out of the side. The answer to where they should go lies in the type of furnace you have: high efficiency or standard efficiency.
A standard-efficiency furnace has an energy efficiency level of below 90%. These types of furnaces usually have a flue pipe that goes up through the roof of your house, since the combustion byproducts are gases. They easily float up through the flue and out of the house.
A high-efficiency furnace has an energy efficiency level of 90% or above and has a exhaust flue pipe that sticks out the side of your house. The horizontal flue pipe drains the liquid byproducts of combustion out.
Process of Installing a Furnace Exhaust Flue (Steps 1 – 4)
Properly installing a furnace exhaust flue properly is the key to warming up your home safely. Here are the four main steps of installing one:
1.) Taking Measurements
Measure the distance from your furnace to your chimney. There should already be a connection on the chimney where the pre-existing flue pipe used to be attached to the previous furnace.
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2.) Purchasing Supplies
Purchase some single-wall galvanized pipe and elbows—as well as a 1-inch, galvanized hangar strap—from your local home improvement store. Make sure they match the size of your furnace’s flue pipe outlet. This is what will make up your flue pipe. You might also require a pipe crimper if you need to cut the flue to fit.
3.) Making Your Furnace Exhaust Flue
Connect the pieces of galvanized pipe by inserting the “crimped end” of each piece into the “non-crimped” end of the pipe. These pieces will be held together by at least four sheet metal screws. Starting at the furnace, install your new flue pipe to the chimney connection. Cut the flue pipe to fit, and crimp the end of the piece you cut with a pipe crimper.
4.) Secure the Furnace Exhaust Flue
Using a 1-inch galvanized hangar strap, hang the flue pipe from the ceiling joists. Next, screw one end up the hanger strap to the ceiling joist and loop it around the flue pipe. Move the other end of the strap up to the ceiling joist to where you want to fasten it. Cut any excess strap off. Screw that end to the ceiling joist. The flue pipe should sit in the middle of the hanger, which will look like the letter U.
Furnace Repair & Installation Services
If you’re having problems with the gas ventilation in your furnace, immediately give our team of technicians a call by phone at (302) 367-7915 to schedule an appointment. We offer trustworthy furnace repair and installation services to households in Delaware, Maryland, and Pennsylvania. Furnace exhaust pipes are important to keep you breathing safe, clean air. ServiceMark’s team of certified contractors provide oil and gas furnace repairs, replacements, and installations. Trust ServiceMark to take care of all of your furnace needs. Call today to get started.
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