Does a Condensate Drain Need Ap Trap

A P-trap is needed to block air and allow condensate to drain properly.

Do you need condensate trap?

All condensate drains go into a trap. The condensate trap is absolutely mandatory for a high-efficiency gas furnace. Since the drain taps into the exhaust system, leaving it open to the air would allow for a potential exhaust/flue gas leak in the living space, which is a big no-no.

How deep should the condensate drain trap be?

If a unit were to be operating at minus 6 inches WC maximum negative plenum pressure then the trap height, per the guidelines shown in Figure 1a, requires 7 + 3½ + 1½ + 1 inches of height from under the floor or about 13 inches below the floor level.