Tankless Venting Upgrade Cost in 2026
The exhaust system is the second-most expensive line item on a tankless install, after the gas line. Most homeowners assume the old chimney flue can be reused. It cannot. Modern condensing tankless units exhaust cool, acidic flue gas that destroys the type B-vent your old tank heater used. This page walks the cost of each vent option in 2026 and explains when each is the right choice.
Why the old flue cannot be reused
A standard 40-gallon tank water heater uses what is called atmospheric venting. The burner heats water in the tank, hot exhaust gas rises by buoyancy through a metal flue, and gravity carries it up the chimney chase and out the roof. The exhaust is hot (350 to 500 degrees Fahrenheit) and dry. The flue is type B-vent: thin galvanized double-wall pipe. It has worked fine in millions of homes for decades.
A condensing tankless water heater works differently. It extracts so much heat from the combustion gases that water vapor condenses inside the heat exchanger and inside the exhaust pipe. The exhaust leaves the unit at 100 to 130 degrees and includes liquid water with dissolved carbonic and sulfurous acids. That mixture corrodes B-vent rapidly. It also lacks the heat needed for atmospheric draft, so the unit uses an internal fan to push exhaust out. The combination of cool acidic condensate and fan-forced flow means the vent must be either plastic (PVC, CPVC, polypropylene) or category IV stainless steel.
The old B-vent gets capped, removed, or sometimes left in place inside a chimney chase that now holds the new vent run as a passive enclosure. The new vent terminates either through a side wall (most common, lowest cost) or through the roof (cleaner visible exterior but more expensive).
Vent type cost comparison
Six common vent configurations and what each costs in 2026 for a standard residential install. Costs include material, labor, fittings, sealant, and exterior termination cap. They do not include drywall patching or chimney chase modifications.
| Vent type | 2026 cost | How it works | Best for |
|---|---|---|---|
| Direct-vent twin pipe (PVC, sidewall) | $250–$550 | Two separate 2-inch PVC pipes, one intake one exhaust, exiting the same wall | Most installations |
| Direct-vent concentric (PVC, sidewall) | $400–$800 | Single penetration, exhaust inside combustion-air pipe | Visible exterior walls |
| Power vent (PVC, sidewall) | $200–$500 | Single exhaust pipe, indoor combustion air | Loose old homes only |
| Through-roof PVC | $600–$1,400 | Vertical run with roof boot and flashing | Interior closet installs |
| Category III stainless (non-condensing) | $700–$1,800 | Single-wall stainless for hot exhaust | Non-condensing budget units |
| Category IV stainless (high-efficiency) | $900–$2,200 | Sealed stainless with condensate handling | Long runs, commercial spec |
| Polypropylene (Centrotherm InnoFlue) | $500–$1,100 | Flexible polypro for retrofit through chimneys | Chimney chase reuse |
Sources: Rinnai, Navien, and Rheem install manuals; HomeAdvisor / Angi quote ranges spring 2026.
PVC vs CPVC vs polypropylene vs stainless
PVC schedule 40 (white). Cheapest material at $4 to $7 per linear foot in 2-inch diameter. Maximum sustained exhaust temperature is 140 degrees Fahrenheit. Approved by most condensing tankless manufacturers including Rinnai, Navien, Rheem, Noritz, and Bosch for vent runs under the manufacturer-specified length. The default choice on a 2026 residential install.
CPVC schedule 40 (cream). Higher temperature rating (200 degrees Fahrenheit) for the same diameter. Costs roughly twice PVC at $9 to $14 per foot. Required by a few manufacturers and a few local codes for the first 6 to 10 feet from the unit where exhaust temperatures peak during startup. Most installs use CPVC only for the transition section if at all.
Polypropylene (Centrotherm InnoFlue, M&G DuraVent PolyPro). Flexible single-wall polypro vent at $12 to $20 per foot. Ideal for retrofits where the vent has to snake through an existing chimney chase. Joints are gasketed instead of glued, which speeds install. Approved by Rinnai, Navien, and several other manufacturers as an alternative to PVC.
Category IV stainless steel (Z-Vent, BIPV). Required for non-condensing tankless (exhaust temperatures over 350 degrees) and for commercial installs. Costs $25 to $45 per linear foot in 4-inch diameter, plus stainless fittings and a stainless termination cap. A 15-foot stainless run can cost $700 to $1,400 in material alone. Most residential homeowners avoid stainless by choosing a condensing unit at the start.
Termination location cost factors
Where the vent exits the building drives both labor cost and aesthetic outcome. Three options matter:
Side-wall termination. The vent exits through an exterior wall, ideally on the same side as the unit. Lowest labor. Requires a 3-inch or 4-inch hole through siding and sheathing, sealing and flashing, and a manufacturer-specified termination cap. The termination must clear setbacks from windows, doors, soffit vents, gas meters, and other obstructions per IFGC 503 and the install manual. Total cost $250 to $700 for a typical 5 to 12 foot horizontal run.
Through-roof termination. Vertical run from unit through ceiling, attic, and roof, with a roof boot and flashing kit. Highest labor (the plumber or a roofer has to work at height). Higher material because vertical runs need more pipe than horizontal. But cleaner exterior aesthetic because the termination is on the roof not the wall, and no setbacks from windows or grade apply. Total cost $600 to $1,400. Necessary when the unit is in an interior closet far from any exterior wall.
Concentric termination. Single penetration, regardless of side-wall or roof. Exhaust pipe runs inside the larger combustion-air pipe right through the wall or roof. Single exterior cap. Best aesthetic. Adds $150 to $300 over twin-pipe for the concentric fitting kit and slightly more labor. Most often chosen on front-elevation walls or stucco/brick exteriors where two penetrations would be ugly.
Vent length limits by manufacturer
Each manufacturer publishes a maximum equivalent vent length in their install manual. Exceed it and the unit voids warranty. Equivalent length adds 5 feet per 90-degree elbow, 3 feet per 45-degree elbow, and the actual measured length of straight pipe.
- Rinnai RU199iN: 70 feet of 2-inch PVC, or 100 feet of 3-inch PVC, per the Rinnai install manual.
- Navien NPE-240A2: 60 feet of 2-inch PVC, 75 feet of 3-inch, per the Navien spec sheet.
- Rheem RTGH-95DVLN-3: 65 feet of 3-inch CPVC, per Rheem published spec.
- Noritz NRC1111-DV: 65 feet of 3-inch PVC per Noritz manual.
- Bosch Greentherm 9000: 60 feet of 3-inch PVC per Bosch spec.
The plumber should map the vent route before quoting. A run with four elbows and 40 feet of straight pipe gives 60 feet of equivalent length. Add a fifth elbow and you push past the limit on some units, forcing 3-inch pipe (which costs more per foot and needs a 3-inch termination cap and a 3-inch wall penetration).
What homeowners often miss
Condensate drain. Condensing units produce one to two gallons of acidic condensate per day during heavy use. That liquid has to go somewhere. The install requires either a gravity drain to a nearby floor drain or laundry standpipe with a neutralizer cartridge, or a small condensate pump if no gravity drain is available. This is a separate line item, typically $75 to $400, covered in detail on the condensate drain installation cost page.
Snow-line clearance in northern climates. The vent termination must sit at least 12 inches above the maximum expected snow depth. In Minnesota, that often means a vent termination 36 inches or more above grade, which sometimes requires routing the vent up and over before terminating, adding length and elbows.
Soffit reentry. Side-wall vent terminations near a soffit vent can recirculate exhaust into the attic. Setback rules per the install manual prevent this, but the practical reality of a tight installation sometimes forces a longer run to clear the soffit. Confirm with the installer that the proposed termination location clears the soffit on the inside of the elevation, not just visually from the outside.