A gas tankless water heater is the most common tankless installation we run across Durham, Chapel Hill, and Raleigh. Natural gas supply is available in most Triangle neighborhoods, recovery is instantaneous, and operational cost is lower than electric resistance alternatives. Drain Express sizes the unit, the gas line, and the venting as a system — not as three separate line items figured out after the unit is already mounted.
Sizing a Gas Tankless Unit for a Triangle Home
Tankless units are sized by flow rate (gallons per minute) at a given temperature rise, not by tank capacity. The relevant calculation is maximum simultaneous demand: how many fixtures could realistically run at the same time in your household, and what is the incoming cold water temperature at worst case (mid-January in the Triangle, roughly 45°F from Jordan Lake supply).
For a 3-bedroom Triangle home with two bathrooms, a dishwasher, and typical usage patterns, a unit delivering 8 to 9 GPM at a 70°F temperature rise handles simultaneous demand without issue. The Navien NPE-240A and Rinnai RU199eN are both in this performance range and are the units we install most frequently on Triangle whole-home replacements.
Gas Line Sizing
This is where most Triangle tankless installations underperform. A Navien NPE-240A at full draw requires roughly 199,000 BTU/hour of gas input. A standard residential 3/4-inch gas supply line can deliver approximately 150,000 BTU/hour at common Triangle supply pressures over a 50-foot run. Installing a high-BTU tankless on an undersized line produces gas starvation under demand — the unit ignites but loses flame mid-cycle, generating error codes and lukewarm water that homeowners attribute to the unit rather than the infrastructure.
We calculate the BTU demand, measure the supply run from the meter, and upsize to 1-inch supply if the calculation requires it. Gas line upsizing adds $400 to $900 to the installation cost depending on run length but is non-negotiable when the math indicates it.
Venting
Gas condensing tankless units (Navien NPE, Rinnai RU series) require PVC or CPVC vent pipe — not the B-vent metal used for tank heaters. Non-condensing units (Rinnai RL, Navien NPN) require stainless steel Category III or IV vent pipe. Pipe diameter is typically 3-inch or 4-inch depending on unit BTU rating and run length. We follow manufacturer specifications for maximum run length and required termination clearances.
Recirculation
For Triangle homes where the water heater is more than 30 feet from the farthest fixture, we install a recirculation pump as part of the tankless installation. Both Navien and Rinnai NPE/RU series units have built-in pump connections. Recirculation eliminates the wait for hot water at distant fixtures and prevents the cold water sandwich effect on short-cycling calls.
Related Services
- Navien Tankless Installation Specifics
- Tank-to-Tankless Conversion
- Tankless Installation Overview
- Installation Cost Reference