A wood stove radiates less heat when the doors are closed because of the way heat transfer works in a closed versus an open system.
When the doors of a wood stove are closed:
Limited Air Supply: Closing the doors restricts the airflow into the stove, reducing the amount of oxygen available for combustion. A proper air supply is necessary for efficient burning of the wood and the release of a significant amount of heat.
Incomplete Combustion: With limited airflow, the wood may not burn as efficiently as it would with the doors open. Incomplete combustion means that not all the wood is converted into heat energy, and some of it is wasted as unburned particles or smoke.
Heat Absorption: The closed doors can absorb and trap some of the heat that would otherwise radiate outwards into the room. The doors act as a barrier, and the heat energy transfers to the metal of the stove, which can then conduct the heat away from the combustion chamber.
Reduced Air Circulation: With the doors closed, there may be less natural convection inside the stove. Convection is the process where the hot air rises, and cooler air replaces it, creating a continuous cycle of airflow that helps distribute the heat. When the doors are closed, this convection process can be inhibited.
On the other hand, when the doors are open:
Increased Airflow: With the doors open, more oxygen can enter the stove, promoting better combustion and a hotter fire.
Better Heat Radiation: The open doors allow the heat to radiate directly from the flames and hot surfaces inside the stove, maximizing the heat output into the room.
Improved Air Circulation: Open doors promote better natural convection inside the stove, ensuring that the heat is distributed more effectively.
It's important to note that while an open door allows more heat to radiate into the room, it also increases the risk of sparks or embers escaping, which can be hazardous. For safety reasons, wood stoves are designed to be operated with the doors closed. However, many wood stoves have a window or vents that allow you to see the flames and enjoy the comforting ambiance of a wood fire while keeping the doors closed for safety and efficiency.