Does a flue have to be straight?

Author: Elizabeth Rosenbaum  |  Last update: Saturday, April 5, 2025

Does a boiler flue have to be straight? Best practice is to install boiler flues that are as short and straight as possible to maximise efficiency. Nevertheless, some boiler models allow for longer boiler flues which sometimes require bends. The number of bends allowed depends on the length of flue allowed.

Can a chimney flue be angled?

If a flue must be angled or offset, the angle can be no more than 30 degrees from vertical. In an offset situation, the joints of the flue liners must be neat and flush forming a smooth interior surface free of excess mortar, ledges and other obstructions.

Does a flue pipe have to go straight up?

First of all, the chimney pipes should be positioned so that they are as vertical as possible. It is important to go through walls or partitions with 45° bends. In addition, horizontal runs and 90° bends should be avoided at all costs, as they cause flue gases and clog the flues.

Does a chimney flue have to be straight?

The entire route from fire to chimney terminal needs to be smooth, straight and vertical wherever possible. Where bends absolutely cannot be avoided, they should be very gentle, a maximum of 2x 45º and the chimney height increased by at least a metre to compensate.

Can you have a bend in a flue?

usually Stove installations will use a 45 degree angle and you should not exceed 4 bends in the overall flue system. The offset measurement should not exceed 20 % of the total chimney length. For example a standard flue height is 4500mm or 4.5 metres therefore the offset should not exceed 900mm.

Do you need a chimney liner?

Can a flue have a 90 degree angle?

Yes, 90-degree bends can be fitted with our condensing boilers if the correct allowance is made on the maximum flue length.

Can you put a bend in a vent pipe?

In conclusion, while plumbing vents are traditionally designed as straight pipes, bends are permissible under certain conditions. Proper planning, adherence to local building codes, and maintaining the required slope are crucial factors when considering bends in plumbing vents.

Do flues have to be straight?

Does a boiler flue have to be straight? Best practice is to install boiler flues that are as short and straight as possible to maximise efficiency. Nevertheless, some boiler models allow for longer boiler flues which sometimes require bends. The number of bends allowed depends on the length of flue allowed.

Can a flue run horizontally?

A horizontal flue, coming out of an external wall, is most commonly used in the UK as it is usually the most direct route from the boiler to the outside.

Can you angle a fireplace flue?

So back to the question at hand: Can we install an angle, or offset, a chimney? The answer is “yes”! It's done every day and is perfectly safe to do so, provided codes are followed and equipment is properly maintained.

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.

Does a vent pipe have to be straight?

Vent pipes must be installed so they stay dry. This means that they should emerge from the top of the drainpipe, either straight vertically or at no less than a 45-degree angle from horizontal, so that water cannot back up into them.

Does a flue need to be vertical?

Most flues are fitted horizontally, although it may be appropriate for flues to be placed vertically on some properties. If the boiler is not fitted to an external wall, for example, a vertical may be used to channel waste gases through and out of the roof space.

Can you offset a chimney flue?

Yes, offsets are available in 15°, 30° and 45° angles. 45° elbows cannot be used for wood burning fireplaces in the USA, Canadian installs can use them. 30° elbows are most common, an easy rule for offsetting is: it takes twice the vertical space to equal the offset distance.

Why are old chimneys slanted?

Masonry Degradation

Your chimney is exposed to the elements 24/7, which take their toll over time. Constant exposure to rain, snow, ice, freezing, and thawing, cause mortar joints to decay and bricks to become loose, which can unbalance the structure, causing it to lean.

Can a balanced flue go up a chimney?

A balanced flue pipe can only work with a balanced flue fire - it cannot be used with a traditional or flueless gas fire. Similarly, if you have a balanced flue fire, you can't use it with a traditional chimney.

Does a chimney flue have to go straight up?

The ideal flue pipe assembly is one that rises straight up from the appliance flue collar and directly into the chimney with no elbows.

Can you have an angled flue?

If bends are unavoidable, then there must be no more than four bends in the length of the chimney. A bend should be no more than 45 degrees from the vertical, with the exception that 90-degree factory-made bends or tees may be treated as two 45-degree bends.

What is the difference between a vertical and horizontal flue?

To find out for sure, nip outside and take a look at the outside wall where your boiler is located, if a pipe pops out then you have a horizontal flue. A vertical boiler flue on the other-hand tends to be found in homes where the boiler isn't on an outside wall, or when the property is a more unusual shape.

Can a chimney flue run horizontally?

There should be no horizontal runs in a flue system and no 90 degree turns. Both of these are hinderences to the draw which is resulting in your poor burning, fumes leaking into the room and blackening glass.

Can a chimney not be straight?

Chimneys should stand tall and straight, not pitch to one side. However, be aware that some builders design chimneys to “tilt” if the fireplace is not centered inside the house. Offset brick courses allow the chimney to exit at the roof ridge, giving the house a symmetrical appearance from the outside.

Can a flue pipe be horizontal?

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.

Can you put a bend in a fireplace flue?

Yes, offset bends are available for the flue systems.

What happens if you bend your exhaust pipe?

Can Improve Engine Performance. A bent exhaust pipe can help maintain your vehicle's exhaust back pressure, which can significantly improve your engine performance.

Can you run a vent pipe horizontal?

While you can indeed run a horizontal vent pipe, you can't do it indefinitely; this is designed to provide your pipes with the ability to drain into the sewer system. The typical rule of thumb according to code requires you to run a horizontal pipe for no more than one-third of the total length.

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