Can a flue pipe be too long?

Author: Demetris Bogan  |  Last update: Tuesday, April 29, 2025

However, when it comes to sizing a flue, bigger isn't always better. Oversized flues can contribute to at least three problems: poor draft, chim- ney corrosion, and freeze/thaw damage to the chimney.

How long can a flue pipe be?

A flue should be 10 to 20 metres long, depending on the type of your boiler, the shape of the flue, and the location where you want to place it.

Can a flue pipe be too large?

Improper flue sizes are a leading cause of poorly drafting fires. A flue that is too small won't allow the fireplace gases to exhaust properly, and a flue that is too large will be cool down too quickly, causing condensation and creosote buildup within the flue.

Does a longer flue draw better?

As you extend your flue you are extending the pressure difference which can only improve the draw and performance of the chimney and stove. This also ensures the draw is not impeded in any way by adjacent buildings and trees which will affect the direction of air across the top of your flue.

What is the 3 2 10 rule for chimneys?

This rule means that your chimney's shortest side needs to be at least 3 feet above the roof penetration, and its top has to be 2 feet higher than any part of the building that's within 10 feet.

What can I do if my fire is too hot, but turning down the airflow causes a smoky chimney?

How far can a chimney pipe run horizontal?

If you plan to use an existing chimney, both its location and the length of its flue will be determining factors. Note these guidelines: The horizontal section of the uninsulated stove pipe should not be more than three-quarters as long as that section of the flue above the point at which the pipe and the flue connect.

What is the 7 times rule for chimneys?

The flow area of the largest common vent or chimney shall not exceed seven times the area of the smallest draft hood outlet. Typically: many water heaters use a 3" flue, the largest area to connect the water heater should be 49" in area or an 8" x 8" chimney tile or 7" round chimney.

How long can a horizontal flue be?

As a general rule, a flue should work effectively when it's up to 10 metres in length. This is usually based on a standard thickness of 60/100mm. For flues that need to be longer than this, it's a good idea to increase the thickness to 80/125mm to ensure that the gases are able to escape easily.

Can a chimney have too much draw?

If the pull is too strong, the heat can quickly be sucked into the chimney. A draft that is too strong can be adjusted with valves, draft regulators (insert pipe or chimney), or restrictors.

How to get more draft from a chimney?

Take a look at some ways to improve the draft in your chimney here:
  1. Check your chimney damper is fully open. ...
  2. Try opening a window. ...
  3. Get your chimney swept. ...
  4. Warm up your chimney. ...
  5. Consider chimney insulation.

What happens if pipe is oversized?

What if a Pipe is too Big? If the pipe is too big, the velocity will be very low. Aside from the excessive materials and their associated cost, the main issue is that a self-cleansing velocity is not reached within the pipe.

Can flue pipe touch wood?

Flues should be at least 25mm from any combustible material (measured from the outer surface of the flue wall, or the outer surface of the inner wall in the case of multi-walled products).

What is the proper flue size?

The Federal Hous- ing Administration (FHA) requires flue liners 1⁄8 the area of the fire- place opening if the chimney is less than 15 feet tall, 1⁄10 for chim- neys 15 feet and taller.

What happens if a flue is too big?

Oversized flues can contribute to at least three problems: poor draft, chim- ney corrosion, and freeze/thaw damage to the chimney. When a gas water heater fires up, it may not have enough heat in its flue gases to push through the large volume of cold air in an oversized flue.

What are the rules for flue pipes?

What are the regulations around boiler flue?
  • 300 mm away from an opening window or air vent.
  • 25 mm below guttering, drain pipes or soil pipes.
  • 300 mm above the ground, roof or balcony level.
  • 2,000 mm below a Velux window.
  • 1,200 mm from an opening, such as a door or window, into the home.

What is the maximum length of chimney pipe?

For the Indian style of cooking, the suction power of the chimney should range between 400 and 1000 cubic metres per hour, depending on the size of your kitchen. The chimney duct should not be more than 12 feet long.

Does a longer chimney draw better?

Generally, the more distance you have between the hot fire and the outside cold air will create a stronger draft. Wood stove manufacturers generally state that the minimum chimney height should be no less than 15'. Based on their tests, 15' is the height where you will start to have an optimal draft.

Why are my logs burning too quickly?

A fire will burn too quickly if there is an excessive air supply. If you find that this is the case please check that the door is closed properly, and that all vents and seals on the stove. Door seals on stoves do need to be replaced on stoves due to wear.

How many bends can a chimney flue have?

Use no more than two right-angle bends in the stovepipe installation. Additional bends cause soot and creosote to collect in the stovepipe or chimney, block flue gas flow, and increase the danger of fire.

What is the maximum length of a flue?

Depending on the boiler model and the type of flue, the maximum length could be between 8m and 14m total, less any deductions for use of bends. The specific allowance for bends is 1.3 metres of flue length for each 90-degree bend and 0.9 metres of flue length for each 45-degree bend.

How long can a horizontal vent pipe be?

It depends on the size. a 1.5 inch vent can run 20 feet in the horizontal. A 2″ vent can run 40 feet in the horizontal. However you can increase it by 1 pipe size over what is required and run indefinitely.

Can a flue pipe run horizontally?

While the allure of horizontally venting a wood-burning fireplace might seem appealing for its simplicity and potential for unique installation locations, it is not feasible due to safety and efficiency concerns.

How many Btus can a 4 inch flue pipe handle?

The 4- inch common vent has a capacity of 138,000 Btu per hour. Reducing the maximum capacity by 20 percent (Section 504.3. 19) results in a maximum capacity for a 4-inch corrugated liner of 110,000 Btu per hour, less than the total input of 135,000 Btu per hour. So a larger liner is needed.

What is the 2 10 rule for chimneys?

This is a pretty basic rule for chimney construction. A chimney must project at least 3 feet above the roof on its shortest side and also be at least 2 feet above any roof structure that is within a 10 foot radius of the chimney. That's it.

How do most chimney fires start?

"Flue fires are perennial". They happen every winter when creosote deposits on the smoke chamber and flue walls are set ablaze by high heat or by flames licking up the chimney. A chimney fire can be exciting and light up the night, but it is NEVER a laughing matter.

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