When shopping for a tankless system, the key concern is efficiency: how well a unit converts fuel into hot water while minimizing standby losses. This guide highlights five top options across electric and gas models, focusing on efficiency ratings, performance, and suitability for different homes. Ideal buyers include: homeowners seeking compact electric units for apartments or small homes; households needing strong flow for multiple fixtures; and those upgrading from bulky storage tanks to space-saving solutions. The table below compares the selected products and their best-use scenarios.
| Product | Best For |
|---|---|
| 14kW Tankless Water Heater Electric ORBEK On Demand | Compact electric setup for small homes or apartments; precise temp control |
| Rinnai RE199iN Non-Condensing Natural Gas | Whole-house gas heating; higher simultaneous demand |
| Stiebel Eltron Tempra 29 Plus Electric | Whole-home electric with multiple presets; space-saving |
| APUS Propane Tankless Water Heater | High flow on propane; multiple fixtures with precise control |
| Rheem RTG Series 8.4 GPM Liquid Propane | High BTU propane option for larger or busier homes |
14kW Electric ORBEK Tankless Water Heater
The 14kW ORBEK electric unit provides on-demand heating with fast response (3 seconds) and a claimed 98% efficiency. It supports up to 3.38 GPM with ±1°F precision control, making it well-suited for single baths or small apartments where space is at a premium. It features LED indicators for status checks and is ETL certified for basic safety compliance. Best for: compact, electricity-based installations where precise temperature control matters. Caution: Electric units may require dedicated wiring and appropriate circuit protection to avoid tripping breakers under peak demand.
Rinnai RE199iN Non-Condensing Natural Gas Tankless
The RE199iN delivers up to 9.8 GPM with 199,000 BTU, focusing on endless hot water for whole-house use. It is non-condensing and designed for indoor installation, with a compact wall-mounted footprint. It includes diagnostic LED displays and service reminders to support maintenance. Best for: larger homes or households with multiple simultaneous hot-water demands. Caution: As a gas appliance, venting requirements and gas line sizing should be assessed for proper installation and safety.
Stiebel Eltron Tempra 29 Plus Electric
The Tempra 29 Plus is an all-electric model rated for 28.8 kW at 240V, designed for whole-home use with no venting required. It supports two temperature memory presets for quick changes between settings and is known for space-saving design. Best for: homes upgrading to electric tankless without gas or venting constraints. Caution: High electrical demand requires a sturdy electrical panel and proper installation by a licensed electrician.
APUS Propane Tankless Water Heater
The APUS propane model delivers 95,000 BTU and 4.42 GPM, designed for 2–3 fixtures with temperature control from 95°F to 140°F. It emphasizes high precision with sensors and smart CPU technology, maintaining ±1°F stability. It reports up to 98% thermal efficiency (UEF 0.81) and utilizes oxygen-free copper heat exchangers. Best for: households needing strong propane performance with tight temperature control. Caution: Propane models require safe outdoor or ventilated indoor installation and proper gas line sizing.
Rheem RTG Series Gas Tankless
The Rheem RTG Series offers 180,000 BTU and 8.4 GPM in a compact indoor propane configuration. It is non-condensing and designed for continuous hot water on demand, suitable for larger households with higher simultaneous demand. Best for: propane-powered homes where strong flow is essential. Caution: Non-condensing units exhaust warm combustion gases; proper venting and clearance are required for safe operation.
Buying Guide: Key Purchase Considerations
- Electric vs. gas heating: Electric units are easier to install where gas is unavailable but may demand higher electrical service. Gas models typically deliver higher flow, suitable for busier homes, but require venting and gas lines.
- Flow rate and demand: Choose a unit that can handle the number of fixtures running simultaneously. Consider the hottest expected water temperature, climate, and usage patterns.
- Efficiency metrics: Look for terms like thermal efficiency and UEF (Uniform Efficiency Factor). Higher values indicate less energy waste during operation.
- Installation space: Tankless systems save space but require appropriate mounting, venting (gas models), and electrical capacity (electric models).
- Maintenance and diagnostics: Units with clear LED diagnostics or diagnostic codes simplify service and longevity planning.
How to Compare Efficient Tankless Models
- Compare GPM at your desired temperature rise to ensure adequate hot water supply during peak usage.
- Assess energy efficiency claims against installation costs and operating costs over time.
- Check compatibility with existing plumbing and whether recirculation is supported or required for your home.
FAQ
- What is the most efficient type of tankless water heater?
Efficiency depends on the model and fuel type; electric tankless units can be highly efficient with precise control, while high-BTU gas models offer robust flow with strong energy performance. Look for high UEF and low standby losses.
- Do tankless water heaters save energy?
Yes, they reduce standby energy losses present in traditional storage tanks, heating water on demand rather than keeping a tank hot constantly.
- Is a higher GPM always better?
A higher GPM means greater peak hot-water flow, but it should match your household demand and the unit’s temperature rise capabilities to avoid cold-water shocks.
- What maintenance is required for tankless models?
Periodic descaling and vent or vent-connection checks for gas models, along with routine electrical inspections where applicable, help maintain efficiency and reliability.
- Can I install a tankless heater myself?
Some electric units may be installed by skilled DIY enthusiasts, but gas models typically require licensed professionals due to venting, gas line, and safety considerations.
- How do I choose between 98% and 95% efficiency claims?
Consider the specific operating conditions and the unit’s efficiency rating under typical home usage. Higher efficiency is generally better, but installation costs and climate also play roles.