Understanding The Importance Of Anti-Downdraft Cowls On Flues For Marine Diesel Stoves


In recent years, stricter regulations for solid fuel stoves have led many boat owners to consider alternative options, such as marine diesel stoves. As a result, we are witnessing an increasing number of diesel stove installations that utilize existing flue parts from the previous solid fuel setups. However, it’s essential to understand that solid fuel flue chimneys and cowls are not necessarily suitable for diesel stoves. In this article, we will explore the reasons behind this incompatibility and the importance of anti-downdraft cowls for marine diesel stoves.

For more general information on flues for boat stove installations, please read our blog post on The Benefits Of Stainless Steel Twin Wall Insulated Flues.

A traditional solid fuel stove chimney and cowl.
  1. Regulatory Changes and the Shift to Diesel Stoves:

Due to environmental concerns and new regulations, the use of solid fuel stoves is becoming more restricted in many regions. Aside from the now very common smoke-controlled zones, which still allow DEFRA approved solid fuel boat stoves, we are also already hearing of some London boroughs attempting to prohibit all solid fuel boat stoves and the emitting of any smoke from a boat stove flue.

One of the alternatives that boat owners often turn to are diesel stoves. These offer an efficient and reliable heating solution while being less polluting and not emitting any visible smoke. However, when installing a diesel stove using the existing solid fuel flue, certain considerations must be taken into account.

  1. The Differences Between Solid Fuel and Diesel Stoves:

Solid fuel boat stoves typically require a simple flue cowl with a simple hat to keep out rainwater. Such cowls are non-restrictive and encourage the upward flow of combustion gases. Downdraft protection is not necessary for solid fuel boat stoves, as they burn much hotter with an amber bed. Downdraft is therefore less likely to occur, and when it does it does not extinguish the fire.

On the other hand, marine diesel stoves function differently, requiring downdraft cowls to protect against strong crosswinds. Diesel vapourising burners work with a thin layer of fuel in the bottom of the burner pot. Because the burner pot is hot, it vapourises the fuel. It is this vapour that burns. Without an anti-downdraft cowl fitted, strong crosswinds can enter the flue and easily extinguish the flame. Many marine diesel stoves are not fitted with thermocouples that stop the fuel flow if the flame goes out. If a downdraft extinguishes the flame, fuel will keep flowing into the burner pot, which will eventually overflow and fuel will enter the cabin, the bilges, etc.

  1. Understanding Downdraft Cowls for Marine Diesel Stoves:

Downdraft cowls are usually part of a flue system specifically designed by the manufacturer for the stove that is being fitted. Though retrofitting is possible, it may not be as effective. We recommend boat owners always use qualified installers who utilise flue parts specifically recommended by the manufacturer. Often there will be different anti-downdraft cowls available depending on the type and location of the boat. For example, an inland waterway vessel will be exposed to less extreme conditions than a boat going to sea.

Anti-Downdraft Flue Cowls


As boat owners seek alternative heating solutions, marine diesel stoves have gained popularity due to their efficiency, reliability, and compliance with stricter regulations. However, when retrofitting a diesel boat stove into the space of an existing solid fuel boat stove, it is of utmost importance to install manufacturer-recommended flue parts with the appropriate anti-downdraft cowl. By understanding these differences, boat owners can ensure the safe and efficient operation of their marine diesel stove, while complying with regulations and reducing environmental impact.