The Eccotemp i-Series is the brand's indoor-rated propane and natural gas tankless lineup — designed for permanent residential installation with sealed combustion and proper venting. Unlike the portable L-series, i-Series units meet UL/ETL listings for indoor installation when properly vented and combustion-air-supplied.
i-Series models and capacities
- i12-LP / i12-NG: 3.4 GPM, 74,000 BTU/hr input — apartments and small homes
- i18-LP / i18-NG: 4.8 GPM, 124,000 BTU/hr — typical 2-bath residences
- i27-LP / i27-NG: 7.1 GPM, 199,000 BTU/hr — 3-bath residences with simultaneous demand
What separates i-Series from L-series
Sealed combustion: i-Series uses concentric or twin-pipe venting that brings combustion air from outside and exhausts combustion products outside — no impact on indoor air quality and no need for room makeup air. Direct vent termination through wall or roof per code-compliant installation. Electronic ignition (vs D-cell battery): requires 120V AC supply to the unit, ignition is reliable and weather-independent.
Installation requirements
Indoor installation requires:
- 120V dedicated circuit (typically 15A is sufficient)
- Gas line sized per BTU rating (1/2" for i12, 3/4" minimum for i18 and i27 — verify with Eccotemp's pipe-sizing chart for actual line length)
- Concentric or twin-pipe venting from unit to exterior wall/roof termination
- Adequate combustion air at termination (no obstructions)
- Water supply with isolation valves (recommended)
- Condensate drain (for higher-efficiency models)
Cold-water-sandwich behavior
Like all tankless units, i-Series produces a brief cold patch when hot draws stop and restart — residual cold water in pipes between the unit and the fixture. Severity depends on pipe length and insulation. For runs over 30 feet, consider a small recirculation system or smart-recirculation pump on a dedicated return.
Efficiency rating
Non-condensing i-Series models operate around 82–84% AFUE. Condensing variants (where available) reach 92–95%. Compared to a tank water heater at 60–65% efficiency, the savings are real but the gas line and venting upgrade costs need to be factored into the payback calculation.
Common installation mistakes
- Undersized gas line — biggest single failure mode. Most i-Series replacing a tank water heater need a gas line upgrade.
- Wrong vent configuration — concentric vs twin-pipe matters; mixing them or using improper materials voids warranty.
- Missing isolation valves — critical for future descaling access in hard-water areas.
- Powering up before water-fill — damages igniter on first call for heat.
Maintenance schedule
Annual descaling is critical in hard-water areas (>5 grains per gallon). Without descaling, heat exchanger scale builds up and reduces capacity, eventually causing fault codes and shortened lifespan. Set a calendar reminder for descaling every 12 months. Inlet screen cleaning quarterly. Burner inspection annually.