Navien

Navien equipment and parts: condensing tankless water heaters, NCB combi-boilers, NFB modular condensing boilers, concentric venting, prefab manifolds, and replacement parts and kits.

Navien built its position on condensing tankless and on the combi — one appliance that carries the heating load and the domestic hot water. The combi is attractive in a small house or a condo because it removes the tank entirely, but it is sized by two independent requirements: heating output for the building and flow for simultaneous fixtures. A combi that heats the house adequately can still be short for two showers, and that mismatch is the most common complaint.

Concentric venting is Navien's standard approach — intake and exhaust in one pipe through one penetration, which is why it suits retrofits with limited wall access. The vent kit is model-specific and the maximum equivalent length is set by the manufacturer's table, not by what fits.

Gas inlet is 3/4" on most units here. A 199,900 Btu/h appliance frequently needs a gas line or meter upgrade, and that check belongs before the order, not after.

Most units are natural gas or propane convertible with the manufacturer's kit.

Sizing a unit? The Navien model comparison puts every model we stock side by side — gas input, UEF, and domestic hot water flow at 35°F, 45°F and 67°F temperature rise, plus dimensions and gas connection sizes.