Lennox DAVE SIGNATURE SL297UHNV Installation Instructions Manual page 26

IMPORTANT
When combining the furnace and evaporator coil
drains together, the A/C condensate drain outlet must
be vented to relieve pressure in order for the furnace
pressure switch to operate properly.
Condensate Trap With Optional Overflow Switch
From Evaporator Coil
HorizontalFurnace4" Min. to 5" Max.above
Optional
FIGURE 38
(Trap at coil is optional)
Drain Pan
condensatedrain connection)
FurnaceCondensate
DrainConnection
Furnace with Evaporator Coil Using a Common Drain
(Unit shown in horizontal left−hand discharge position)
Evaporator
Coil
Condensat e Drai n
Connection
Piping from furnace and evaporator coil must slope
down a minimum 1/4" per ft. toward trap
Furnace with Evaporator
Coil Using a Common Drain
(Trap at coil is optional)
(1" min. to 2" Max.above
condensatedrain connection)
Condensate
Drain Connection
4"min
5"max
5' max.
PVC Pipe Only
Figure 40
Page 26
Evaporator drain
line required
FIGURE 39
(4" min. to 5" Max.above
condensatedrain connection)