Water Heater Vent Sizing Calculator
Vent pipe diameter for a gas water heater.
Enter your values
ⓘ Live results
Results
- Minimum vent diameter
- 3 in Type B
- Vertical height entered
- 15 ft
- Lateral length check
- Within typical limit
- Note
- Always confirm against the manufacturer's specific vent capacity table
Quick answer
Most standard gas water heaters (30,000-75,000 BTU/hr) vent through a 3 or 4 inch Type B vent depending on total vent height and lateral length, per vent tables.
Vent size selected from BTU/hr, vent height and lateral length capacity tables
How to use the Water Heater Vent Sizing Calculator
- 1Enter the water heater's BTU/hr input rating.
- 2Enter the vertical vent height and any lateral run.
- 3Cross-check the result against the manufacturer's vent sizing table, since actual limits vary by model.
Worked example
Using the values the calculator loads with:
Inputs
- Water heater input40000 BTU/hr
- Vertical vent height15 ft
- Lateral vent length2 ft
Results
- Minimum vent diameter3 in Type B
- Vertical height entered15 ft
- Lateral length checkWithin typical limit
- NoteAlways confirm against the manufacturer's specific vent capacity table
Frequently asked questions
Can I always use 3 inch vent?
Only for smaller water heaters and adequate vent height — larger inputs or long laterals need 4 inch or bigger.
What about power-vented models?
Power vent and direct vent water heaters use PVC/CPVC per the manufacturer's specific sizing, not standard B-vent tables.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.