Retrotec USACE - Manual (Page 257)

Appendix D D127
D.7.8.14 Furnaces with Continuously Lit Pilot (Waste)
Figure D205. Furnace with electronic pilot
ignition. Figure D204. Use of continuously lit pilots.
Older ovens and furnaces may have pilots that are continuously lit when the
unit is not fi ring (Figure D204). They are used to light the main burner when
the furnace or oven is brought back online. These pilots can be replaced by
those that have spark ignition (Figure D205), saving fuel when the oven or
furnace is not being used.
D.7.8.15 No Automatic Stack Damper (Ineffi ciency)
Figure D206. Combustion air exhaust ducts on
heat treat ovens having no stack damper.
A stack damper is used to isolate a furnace or oven when not in use. Closing
these dampers when the unit shuts down prevents the loss of the retained
heat inside the furnace or oven after fi ring. Without a closed stack damper, air
would continue to fl ow through the furnace and up the stack, taking heat from
the system (Figure D206). Also, cold air could enter the furnace down from
the stack, posing a freezing problem during below-freezing weather.