Condensate Drain Trap Depth from Fan Static
The dimension condensate-drain only mentions in prose. Manufacturer trapping geometry: draw-through H = 1 in per 1 in of negative static plus 1 in, outlet leg J = half of H, and total clearance L = H + J + pipe + insulation; blow-through H = static plus 1/2 in. A 2-in w.c. draw-through unit needs a 3-in trap, 1.5-in outlet leg, and 6 in of room under the pan. Both errors bite: too short loses the seal at start-up and pulls drain air into the airstream, too tall will not drain against the negative pressure.
Formula and source
Draw-through: H = (1 in per 1 in of maximum negative static) + 1 in; J = H/2; L = H + J + pipe diameter + insulation. Blow-through: H = 0.5 in + maximum total static; K = 0.5 in minimum.
Manufacturer condensate-trapping engineering guidance (Trane condensate-trapping bulletin), by name - the named dimensions H, J, K, and L are taken from its figures.
Audience
This tile is built for hvac and the adjacent professions in the HVAC group. The interactive calculator runs entirely in your browser. No account, no fee, no advertising, no tracking.
Related tools
Posture
Rough Logic answers the math question the working professional asks on the job. The site is a calm, fast, ad-free, account-free, ever-free reference. It does not interpret code. It does not replace the licensed professional. It does not store your inputs. The Authority Having Jurisdiction governs all installations and inspections.