Water-Heater T&P Relief and Discharge
Checks a water heater's T&P valve against its input and sizes the discharge pipe.
Example
You enter
- Heater input rating (BTU/hr) 50000
- T&P valve marked relief capacity (BTU/hr) 150000
- Valve discharge-outlet size 0.75
You get
- Minimum discharge pipe 0.75
- Rating margin (Btu/h) 100000
Checked against published worked examples from: IPC 2021 Section 504 / ANSI Z21.22.
Details, formula, and sources
ScopeChecks the T&P relief valve's rating against the heater input and reports the IPC 504.6 discharge-pipe size and requirements.
Formula or tablerating_ok = valve_rating >= heater_input; discharge_in = valve outlet (never reduced). Output is a pass/fail and the IPC 504.6 discharge checklist, not a continuous quantity.
Source and editionIPC 2027 Section 504 (504.5 valve relieving capacity vs heater input, 504.6 discharge piping) and ANSI Z21.22 / CSA 4.4 by name; first-principles comparison.
Free accessIPC 2027 and 2021 free read-only at codes.iccsafe.org. The discharge requirements are public code text.
What governsEstimate. AHJ and licensed professional govern.
API field namesheater_input, valve_rating, outlet_size, discharge_in, rating_margin_btuh
- Discharge size the full valve outlet (typ. 3/4 in), never reducedIPC 2027 Section 504.6 (unchanged from 2021)
- Rating rule valve marked relief capacity >= heater input ratingIPC 2027 Section 504.5 (unchanged from 2021) / ANSI Z21.22