3196 



Chapter 26 



BYPASS 

 DAMPER. 



EITHER 



SECONDARY 

 /AIR IS 

 /OFTEN 



INTRODUCED 

 HERE 



DIAGONAL 



ACROSS 



BYPASS 

 DAMPER 



EITHER 



SECONDARY 

 AIR IS 

 OFTEN 

 INTRODUCED 

 HERE 



EITHER 



DOWN 



"S 



Figure 26-22. — The five basic airflow patterns found in domestic stoves. Stoves with 

 both the across- and down-draft flow patterns usually require a bypass damper to 

 prevent smoke from entering the room when the stove door is opened. (Drawing after 

 Lew.7). 



be supplied above the burning wood for more efficient combustion. Examples of 

 this flow pattern include the Ashley 25HF, Fisher and drum stoves (Shelton 

 1976). 



In the across pattern, air enters the stove at the bottom front but moves 

 horizontally across the wood to exit at the lower back. Considerable turbulence 

 occurs above the burning wood and volatile gases are forced through the hot 

 coals or flames at the back of the combustion chamber. Secondary air is usually 

 provided at this point. Stoves with both the across and downdraft flow patterns 

 usually require a bypass damper to prevent smoke from entering the room when 

 the stove door is opened. Many stoves using the across flow are airtight and have 

 large fuel capacities so that refueling is not necessary for long periods (Shelton 

 1976). 



In downdraft stoves, air enters the stove above the grate and passes down 

 through the grate along with emerging volatiles produced from the burning 

 wood. Secondary air can be provided at a number of points, often at the bottom 

 of a baffle plate at the back of the stove. Combustion is then completed in a 

 secondary chamber. This design is one of the better ones for efficient burning of 

 wood. Downdraft stoves are usually airtight and can operate for long periods 

 between fueling (Shelton 1976). 



Wood usually rests directly on the firebox floor in the S-flow stoves. A 

 horizontal baffle extends from the back of the stove and prevents air flow and 

 volatile gases from leaving the combustion area directly. The S-flow provides 



