Tankless gas heaters deliver on-demand hot water while saving space and energy compared to traditional tanks. Below is a quick comparison table of five highly rated options selected for their flow rates, fuel compatibility, installation flexibility, and safety features.
| Product | Flow / BTU | Indoor / Outdoor | Key Feature |
|---|---|---|---|
| Rinnai RX199iN | Up To 11.1 GPM / 199,000 BTU | Indoor Or Outdoor | Condensing, High UEF .98 |
| Rheem RTG-95DVLN-3 | 9.5 GPM | Indoor | High Efficiency, Water Saving Setting |
| Rheem RTGH84DVLN | Up To 8.4 GPM / 157,000 BTU | Indoor | Wide Temp Range, Electric Ignition |
| FOGATTI Instagas Comfort 180S | Up To 8.1 GPM / 180,000 BTU | Outdoor | Precision Temp Control, Remote Panel |
| VELPAX Outdoor 5.26 GPM | 5.26 GPM / 120,000 BTU | Outdoor | Stainless Steel Body, Digital Display |
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Rinnai RX199iN Condensing Tankless Water Heater
Rinnai RX199iN is a high-capacity, condensing tankless gas heater designed for both indoor and outdoor installation. The model supports natural gas or propane via a Smart Sense gas control and can deliver up to 11.1 GPM, suitable for multiple simultaneous fixtures.
Key design facts include a compact footprint described as the size of a small suitcase, an easy-to-use interface, and a Quick Flush feature for simplified maintenance. The unit boasts a high UEF .98 efficiency rating, improving energy use compared to non-condensing units.
Installation notes: outdoor placement requires an RX-OVC vent cap and the unit supports Versa Vent. Wi‑Fi control is possible using Rinnai’s Control-R module (sold separately). Maintenance advantages include condensate management typical of condensing units and service-friendly access for flushing.
Rheem RTG-95DVLN-3 High Efficiency Tankless Heater
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The Rheem RTG-95DVLN-3 is a high-efficiency indoor tankless natural gas heater rated for 9.5 GPM. It emphasizes continuous hot water delivery for whole-house applications and multi-appliance use.
Standout features include an energy-saving operation that runs only when hot water is needed and a Water Saving Setting claimed to reduce annual water waste. The unit targets homeowners seeking steady flow for showers and dishwashing without tank standby loss.
Practical considerations: this model is a non-condensing indoor heater, so proper venting and combustion air support are required. The unit is positioned for installations where high flow and simplicity are priorities.
Rheem RTGH84DVLN 8.4 GPM Indoor Tankless Heater
The Rheem RTGH84DVLN provides up to 8.4 GPM and a max input around 157,000 BTU. It supports temperature settings from 100°F to 140°F, with a factory default of 120°F, and features electric ignition for consistent start-up.
This unit is suited for medium-sized homes or applications where moderate simultaneous demand exists. The adjustable temperature range is useful for households that need precise control for both comfort and safety.
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Installation details: as an indoor model it requires appropriate venting and electrical connection for the ignition system. The listed flow range (0.4–8.4 GPM) helps match the heater to fixture demand to avoid temperature fluctuations at low flow.
FOGATTI Instagas Comfort 180S Outdoor Tankless Heater
The FOGATTI Instagas Comfort 180S is an outdoor-focused tankless gas heater delivering up to 8.1 GPM and driven by 180,000 BTU. It is engineered for outdoor durability with a bottom-mounted fan to prevent smoke backflow and ensure stable combustion.
This model highlights precise temperature control via water servo technology and advanced sensing to maintain temperature within ±1°F. It includes a remote control panel for indoor adjustment and a four-stage combustion system to optimize performance in varied weather.
Outdoor installation benefits include fewer venting constraints and improved longevity in suitable climates. Users should verify local codes for outdoor gas appliance placement and ensure frost protection measures if required.
VELPAX Outdoor 5.26 GPM Natural Gas Tankless Heater
The VELPAX Outdoor tankless heater offers 5.26 GPM with a 120,000 BTU rating and a stainless steel body designed for corrosion resistance. It operates exclusively on natural gas and includes an LED digital display for temperature control between 95°F and 149°F.
Safety features listed include flame failure device, anti-freeze protection, and overheating protection. The unit claims low minimum water pressure operation (3.6 PSI) and an oxygen-free copper heat exchanger for efficient heat transfer.
Ideal uses are smaller homes, supplemental supply, or locations where an outdoor unit reduces venting complexity. The digital display simplifies temperature adjustments and monitoring during operation.
Buying Guide: How To Choose A Tankless Gas Heater
Choosing the right tankless gas heater depends on flow requirements, fuel type, installation site, efficiency, and safety features. Use the guidance below to compare options effectively.
Flow Rate And Household Demand
- Calculate Peak Demand: Add GPM for fixtures used simultaneously (e.g., shower ~2.5 GPM, dishwasher ~1–1.5 GPM). Choose a unit with a sustained GPM above peak demand to avoid temperature drops.
- Allow Margin: Select a heater with slightly higher GPM than calculated peak to handle colder inlet temperatures or increased future demand.
Fuel Type And Availability
- Natural Gas vs Propane: Confirm available fuel and select a model rated for that fuel. Some units (like the Rinnai RX199iN) support both with proper control settings.
- Venting Requirements: Indoor non-condensing units typically require direct venting; condensing models have different vent materials due to acidic condensate.
Indoor Or Outdoor Installation
- Outdoor Units: Reduce venting needs and can be easier to install in some locations. Check weather and freeze protection requirements.
- Indoor Units: Require proper combustion air and venting; condensing indoor units may offer higher efficiency but need condensate management.
Efficiency And Operating Costs
- UEF And Condensing: Higher UEF ratings and condensing technology (e.g., Rinnai RX199iN’s .98 UEF) mean better fuel-to-water efficiency and lower operating cost.
- On-Demand Operation: Tankless units only fire when hot water is needed, eliminating standby losses common with storage tanks.
Safety And Certifications
- Third-Party Certification: Look for CSA, UL, or other recognized certifications indicating compliance with safety standards.
- Built-In Protections: Features like flame failure protection, overheat protection, and freeze protection improve safe operation.
Control, Connectivity, And Maintenance
- Controls: Digital displays and remote panels provide easier temperature adjustments and diagnostics.
- Wi‑Fi Options: Some models support optional Wi‑Fi modules for monitoring and remote control (confirm compatibility and availability).
- Maintenance: Periodic flushing is required to remove scale. Quick-flush features reduce service time; condensing units may require additional condensate management.
Installation Considerations
- Professional Sizing: Have a licensed plumber or HVAC technician confirm gas line sizing, venting type, and electrical requirements for ignition systems.
- Local Codes: Verify local building codes and permit requirements for gas appliances and outdoor installations.
- Gas Supply Capacity: Ensure household gas service can supply the BTU input of the chosen unit without affecting other appliances.
Comparison Perspectives
- High Capacity & High Efficiency: Choose condensing high-BTU options (Rinnai RX199iN) for large households seeking max GPM and efficiency.
- Balanced Whole-House Performance: Non-condensing high-flow Rheem models suit homes needing consistent multi-fixture supply with simpler venting considerations.
- Outdoor Simplicity: Outdoor models such as FOGATTI and VELPAX reduce indoor venting complexity and are good for milder climates or installations where exterior mounting is preferred.
- Compact Or Lower Demand: Smaller, lower-GPM units are appropriate for apartments, RV conversions, or homes with limited simultaneous use.
Using flow calculations, confirming fuel/venting compatibility, and evaluating efficiency and protection features will help align a tankless gas heater to your home’s needs. For final selection and safe installation, consult a licensed professional to verify gas supply, venting, and permit requirements.
Tips for Getting the Best HVAC Prices
- Prioritize Quality Over Cost
The most critical factor in any HVAC project is the quality of the installation. Don’t compromise on contractor expertise just to save money. - Check for Rebates
Always research current rebates and incentives — they can significantly reduce your overall cost. - Compare Multiple Quotes
Request at least three estimates before making your choice. You can click here to get three free quotes from local professionals. These quotes include available rebates and tax credits and automatically exclude unqualified contractors. - Negotiate Smartly
Once you've chosen a contractor, use the proven strategies from our guide — How Homeowners Can Negotiate with HVAC Dealers — to get the best possible final price.