An open flue can allow significant heat loss, especially in cold weather. It is recommended to close the flue when the appliance is not in use to prevent heat loss. The smallest flue pipe size used for residential appliances is typically 2 inches in diameter. However, larger sizes are more common for water heaters and heating appliances. The number of bends allowed in a flue pipe depends on the appliance’s BTU output, the height of the flue, and the manufacturer’s guidelines. Each bend adds resistance and can affect draft performance. The 2-10 rule for chimneys is similar to the 3-2-10 rule and refers to clearance distances required between a chimney and nearby structures. The chimney should be at least 2 feet higher than any roof within 10 feet horizontally. Twin wall flues will heat up when in use as they transport the hot stove gases away from the appliance, the outer part of the flue can be over 90o C or 194o F. The temperature of the twin wall flue will vary depending on:

A flue pipe can be too large if it exceeds the manufacturer’s recommendations for the appliance’s BTU output and flue height. An oversized flue can cause draft problems and reduce efficiency. The appropriate flue size for a water heater depends on the water heater’s BTU output and the manufacturer’s recommendations. Common sizes are 3 inches and 4 inches in diameter.Flue installation should be done by a qualified professional to ensure proper sizing, venting, and compliance with building codes for safety and efficiency. Credit subject to status and affordability. Terms & Conditions Apply. Credit is provided by Novuna Personal Finance, a trading style of Mitsubishi HC Capital UK PLC, authorised and regulated by the Financial Conduct Authority. Financial Services Register no. 704348. The register can be accessed through www.fca.org.uk The size of the flue you need depends on the type of appliance you are venting, the fuel used, and the manufacturer’s recommendations. Generally, flue size is determined by the BTU output of the appliance and the length of the flue run.

A larger flue can provide better draft and improve the appliance’s efficiency, but it must be proportionate to the appliance’s BTU output and follow the manufacturer’s recommendations. Twin Wall Flue by Flue Direct, the leading UK supplier of HETAS approved flues; twin wall flue pipe, flexible flue liner, flue for wood burners and all flue supplies for log burners, multi fuel stoves, wood burning stoves, fires, commercial and biomass boilers.The angle of a flue pipe should have a minimum upward slope of 1/4 inch per foot to promote proper venting. For a water heater, the size of the chimney liner depends on the BTU rating of the water heater and the height of the chimney. It is essential to follow the manufacturer’s guidelines or consult a professional to determine the appropriate size. What size flue do i need? HETAS regulations state that there is a minimum flue size of 150mm / 6 inch for any stove (on which wood could be burnt) unless it is Defra Exempt. Therefore, you may need to increase your flue size from your stove outlet using an increaser e.g 5 – 6 inches. Please talk to us for further information if required.