Why venting changes with tankless
A typical garage tank in Fullerton vents through a metal flue that rises through the roof and relies on hot exhaust to draft upward. Most gas tankless units use a fan to push exhaust out instead, and their venting has to match that design. Reusing an old tank flue is generally not allowed unless the manufacturer specifically permits it.
Condensing tankless units pull extra heat out of the exhaust, which cools it enough to form condensate. That cooler exhaust can often run in plastic vent pipe specified by the manufacturer. Non-condensing units send hotter exhaust out and generally need a vent material rated for that heat, again as the manual specifies.
Condensing and non-condensing at a glance
Condensing unit
- Cooler exhaust; vent material per manual, often a plastic type
- Produces acidic condensate that needs a drain
- May require a condensate neutralizer
- Often allows longer or more flexible vent runs
Non-condensing unit
- Hotter exhaust; vent material rated for heat per manual
- No condensate drain needed in most cases
- Vent pipe may be harder to route through tight spaces
- Shorter allowable runs in some designs
What a plumber should check on the vent route
- Total vent length and number of elbows are within the manufacturer's limits
- Termination clearances from windows, doors, air intakes and property lines
- The vent slopes the way the manual requires so condensate drains correctly
- Supports and wall penetrations are sealed and secured
- Intake air, if the unit is direct-vent, is piped as specified
- The old tank flue is capped or removed properly if no longer used
Common Fullerton vent locations
| Install spot | Typical vent approach | Things to watch |
|---|---|---|
| Garage wall | Horizontal vent through the side wall | Clearance to windows, doors and the driveway |
| Old tank closet indoors | Vent through wall or roof per manual | Combustion air, length limits and condensate drain access |
| Exterior wall (outdoor model) | Built-in vent cover, no vent pipe | Clearances to openings and weather exposure |
Ask about the vent
- Is this unit condensing or non-condensing, and what vent material does it require?
- Where will the vent terminate, and does it meet the listed clearances?
- What happens to the old flue through the roof?
- Will the vent work be covered by the permit and inspection?
Common questions
Can I reuse my old water heater flue?
Generally not for a fan-assisted tankless unit unless the manufacturer allows it. Ask your plumber to show you the manual's venting section.
Is an outdoor tankless model an option?
Some models are made for exterior walls and need no vent pipe. Clearances to openings still apply, and the plumber should confirm the spot.
Why does a condensing unit need a drain?
Cooling the exhaust produces acidic water that must be drained as the manufacturer and code require, sometimes through a neutralizer.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.