20
+
+
+
Condensing
Furnace
-
-
-
-
-
Evaporator Coil
+
+
+
< +
< +
< +
+
Blower
-
   + = Positive pressure
< + = Pressure lower than areas with +
 − = Negative pressure
Blower creates positive pressure.
Positive pressure extends into coil
condensate drain (no trap).
Furnace condensate does not flow
consistently when drain is at positive
pressure.
+
DIRECTION
 
OF
 
AIRFLOW
+
+
+
+
+
+
+
+
+
+
Condensing
Furnace
-
-
-
-
-
Evaporator Coil
+
+
+
< +
< +
< +
+
Blower
-
3/4”
 
PVC
1/2
 
3/4
1/2”
 
CPVC
 
or
 
larger*
   + = Positive pressure
< + = Pressure lower than areas with +
 − = Negative pressure
+
3/4”
 
PVC
DIRECTION
 
OF
 
AIRFLOW
+
+
+
+
1/2
 
3/4
 
3/4
 
3/4
Open
standpipe
+
+
 
3/4
+
+
+
+
Condensing
Furnace
-
-
-
-
-
Evaporator Coil
+
+
+
< +
< +
< +
+
Blower
-
3/4”
 
PVC
 
3/4
1/2”
 
CPVC
 
or
 
larger*
   + = Positive pressure
< + = Pressure lower than areas with +
 − = Negative pressure
+
3/4”
 
PVC
DIRECTION
 
OF
 
AIRFLOW
+
+
+
+
 
3/4
 
3/4
 
3/4
 
3/4
 
3/4
+
+
+
+
+
+
+
++
+
A14532
Fig. 17 -- Example of Field Drain Attachment (Not Allowed)