| 165 / | HD | HEAT EXCHANGE |
| DIG 92 | DD | WITH VALVE OR MOVABLE DEFLECTOR FOR HEAT EXCHANGE FLUID FLOW {6} |
| DIG 109 | DD | .~ With by-pass of heat exchanger or heat exchanger section {2} |
| DIG 110 | DD | .~.~ Bypass within or surrounds heat exchanger {4} |
| DIG 111 | DD | .~.~.~ Heat exchanger enclosing a fluid conduit confining second heat exchange fluid {1} |
| DIG 112 | | .~.~.~.~ Stove pipe drum having air draft passage for heating ambient air |