Condensing versus non-condensing tankless water heaters affects efficiency, venting, and long-term costs. This guide compares five top options to help American buyers decide which system fits their home, household size, and venting realities. Non-condensing units are typically simpler and cheaper upfront, while condensing models maximize energy savings through heat recovery. The best choices below balance performance, installation practicality, and value for families, renters, and homeowners upgrading from older tank systems.
Summary table of selected products
| Product | Type | GPM | BTU | Indoor/Outdoor | Best For |
|---|---|---|---|---|---|
| Rheem RTG Series 7.0 GPM | Non-Condensing | 7.0 | 160,000 | Outdoor | Small to mid-size homes needing outdoor, vent-free setup |
| Rheem RTG Series 8.4 GPM | Non-Condensing | 8.4 | 180,000 | Indoor | Indoor installation with direct vent; multi-shower needs |
| ThermoMate Condensing Tankless | Condensing | 5.28 | 114,000 | Indoor | Condensing efficiency with dual heat exchangers |
| Rheem Prestige Condensing RTGH | Condensing | 11.0 | >190,000 | Indoor | High-demand households; built-in recirculation |
| Rheem RTG Series 9.5 GPM | Non-Condensing | 9.5 | 199,900 | Outdoor | Large homes needing outdoor, vent-free operation |
Rheem RTG Series 7.0 GPM Outdoor Non-Condensing
- Non-condensing with 0.82 UEF for energy efficiency
- 7.0 GPM at 35°F rise, 160,000 BTU/hr
- Outdoor installation eliminates venting; ideal for large families in homes with outdoor space
- Best for homes where outdoor mounting is feasible and venting constraints exist
Best for: Homeowners seeking a straightforward outdoor setup with solid performance for 2–3 simultaneous showers. Limitations: Outdoor units may require weatherproof mounting and protection from the elements; consider a proper enclosure.
Rheem RTG Series 8.4 GPM Indoor Non-Condensing
- Indoor installation with direct vent system
- 8.4 GPM at 35°F rise; 180,000 BTU/hr
- Space-saving wall-mount design; supports 3–4 water points
- Best for: Homes that require indoor installation and multiple simultaneous hot water points.
Limitation: Indoor venting adds installation considerations; ensure proper clearance and venting path.
ThermoMate Condensing Tankless Indoor
- Condensing 0.86 UEF with dual heat exchangers
- 5.28 GPM and 114,000 BTU; two showers simultaneously at comfortable temperatures
- Advanced safety protections; frost protection down to 41°F
- Best for: Households seeking higher efficiency and compact indoor installation with two simultaneous points of use
Caution: Condensing units rely on venting for exhaust and condensate management; ensure proper drainage and vent installation.
Rheem Prestige Condensing RTGH Indoor
- Condensing technology with built-in recirculation
- 11.0 GPM capacity; high efficiency for busy homes
- Compact design suitable for tank replacements
- Best for: Larger households needing rapid hot water recovery and a recirculation feature for comfort
Limitation: Higher initial cost typical of condensing, multi-point systems; ensure compatibility with existing plumbing and recirculation needs.
Rheem RTG Series 9.5 GPM Outdoor Non-Condensing
- Outdoor non-condensing, high output
- 9.5 GPM at 35°F rise; 199,900 BTU/hr
- Vent-free outdoor installation with durable cabinet
- Best for: Large households with outdoor installation where venting is a constraint
Suggestion: Choose this when you need substantial simultaneous hot water in an outdoor setup without complex venting.
Buying Guide: Condensing vs Non-Condensing Tankless Water Heaters
What matters most when choosing between condensing and non-condensing models? Consider energy efficiency, installation location, venting requirements, and peak hot-water demand.
Energy efficiency and operating costs
Condensing units typically offer higher efficiency (UEF around 0.86 or more) by reclaiming waste heat. This can reduce long-term energy costs, especially in households with high hot-water usage. Non-condensing models are generally reliable, with solid efficiency around 0.82 UEF, and may have lower upfront costs.
Installation location and venting
Outdoor models avoid indoor venting but require weather protection and proper drainage for condensate in condensing units. Indoor condensing heaters demand venting and admission of fresh air, plus condensate handling. Non-condensing indoor units simplify venting but still need proper exhaust paths if installed indoors.
Hot-water demand and sizing
Higher GPM ratings indicate better ability to supply multiple showers at once. For homes with many simultaneous users, larger outdoor units (like 9.5 GPM or 11.0 GPM) or condensing models with recirculation may provide more consistent comfort.
Cost considerations
Condensing units often cost more upfront due to advanced heat exchangers and controls but can save more on energy bills over time. Non-condensing units may offer lower initial price and easier service in some areas.
Maintenance and lifecycle
Condensing systems may require condensate drainage maintenance and periodic inspection of heat exchangers. Non-condensing units are typically simpler, with fewer moving parts that can affect efficiency over the long term.
Frequently Asked Questions
- What is the main difference between condensing and non-condensing tankless heaters? Condensing models recover and reuse waste heat to improve efficiency, while non-condensing units vent exhaust directly without heat recovery.
- Which is best for outdoor installation? Outdoor non-condensing models offer vent-free operation and easy installation where weather protection is available; compatible condensing outdoor units also exist but require condensate management.
- Do condensing units save more energy over time? Generally yes, due to higher efficiency, but savings depend on usage, climate, and installation costs.
- Is 11 GPM necessary for a large family? For households with multiple simultaneous showers and hot-water points, 11 GPM or higher is often beneficial, especially in cooler climates or with long draw lengths.
- Do these systems require professional installation? Yes. Tankless heaters involve gas connections, venting, electrical supply, and proper clearances; improper installation can affect safety and performance.
For buyers prioritizing energy efficiency and future savings, condensing models with higher GPM ratings and integrated recirculation can be compelling. For those prioritizing upfront cost and simple venting, non-condensing options remain solid, especially in suitable homes with straightforward installation.