Answering the need for reliable, on-demand hot water, these non-tank (tankless) water heaters provide continuous hot water without storing it. They’re best for households that want energy efficiency, space savings, and fewer cold-water surprises during showers. The top picks below are especially suited for homes with 2–4 bathrooms or for users replacing aging tank systems. The buyer table after the intro highlights each option at a glance.
| Product | Type | Best For | Key Benefit |
|---|---|---|---|
| Rheem RTG Series 7.0 GPM Natural Gas Indoor | Gas Tankless (Indoor) | Mid‑size homes, 2–3 simultaneous showers | Compact indoor unit with solid efficiency |
| Rheem RTG Series 8.4 GPM Natural Gas Outdoor | Gas Tankless (Outdoor) | Homes needing higher flow outdoors | Outdoor installation, higher flow |
| Rheem RTG Series 7.0 GPM Liquid Propane Outdoor | Propane Tankless (Outdoor) | Off-grid or propane-only setups | Outdoor, propane fuel access |
| Rheem RTG Series 7.0 GPM Natural Gas Outdoor (Two Units) | Gas Tankless (Outdoor) | Outdoor multi-point hot water | Outdoor sizing for 2–3 points |
| Rheem RTG Series 7.0 GPM Natural Gas Outdoor (Alternative Listing) | Gas Tankless (Outdoor) | Outdoor, compact option | Similar specs with different installation context |
Rheem RTG Series 7.0 GPM Natural Gas Indoor
This indoor unit provides 7.0 GPM at a 35°F rise, delivering up to 160,000 BTU/hr. It is designed for whole‑house use and supports 2–3 simultaneous showers. The non‑condensing design helps reduce upfront costs while maintaining energy efficiency. Best for mid‑sized homes with indoor installation needs and a direct vent system.
Who it’s best for: households looking to replace an aging tank with a compact indoor tankless option and who want reliable hot water without venting complexity for outdoor units. Caution: Indoor installations require proper venting and clearance; verify space and vent compatibility with local codes.
Rheem RTG Series 8.4 GPM Natural Gas Outdoor
This outdoor model delivers 8.4 GPM at a 35°F rise, equating to about 3–4 simultaneous showers in many homes. Outdoor installation eliminates venting concerns and provides a durable exterior cabinet for rugged use. It is a solid choice for larger families or multi‑bath homes that need higher flow without indoor space constraints.
Who it’s best for: homes with space outdoors and a demand for higher hot-water flow. Limitation: outdoor units require protection from the elements and appropriate drainage around the venting area.
Rheem RTG Series 7.0 GPM Liquid Propane Outdoor
This propane outdoor unit offers 7.0 GPM at a 35°F rise with 160,000 BTU/hr output. Like other outdoor models, it eliminates venting inside and features a robust metal cabinet designed for exterior installation. Best for households that rely on propane as a primary fuel source or where indoor venting is limited.
Who it’s best for: homes with propane access and a need for outdoor installation. Caution: Ensure proper propane supply lines and annual maintenance checks for outdoor units.
Rheem RTG Series 7.0 GPM Natural Gas Outdoor
This outdoor model mirrors the 7.0 GPM capacity and 160,000 BTU/hr output, optimized for whole-house hot water with two to three water points running simultaneously. It maintains energy efficiency with a non-condensing design and a sturdy outdoor cabinet for reliable operation.
Who it’s best for: outdoor installations where venting is minimized and space is limited. Limitation: outdoor exposure may require additional weatherproofing and routine maintenance checks.
Rheem RTG Series 7.0 GPM Natural Gas Outdoor (Alternate)
An alternate outdoor listing of the same 7.0 GPM gas tankless system for outdoor installation. It shares the same benefits: instant hot water, energy efficiency, and space-saving design. Best for: those comparing outdoor models with similar specs. Caution: confirm compatibility with your home’s venting and gas supply.
Buying Guide: Non-Tank Water Heaters
How to choose the right tankless system
- Flow needs: Calculate your peak GPM usage (e.g., showers, sinks, appliances) to select a model that can maintain hot water for simultaneous points.
- Fuel type and venting: Natural gas units require proper venting; outdoor models avoid interior venting but must be weatherproofed. Propane units suit propane systems or off‑grid homes.
- Installation location: Indoor units save space but require venting; outdoor units provide easier venting but need weather protection.
- Energy efficiency: Look for high Uniform Energy Factor (UEF) ratings; non‑condensing designs usually balance cost and efficiency.
- Maintenance access: Choose units with accessible service panels and straightforward replacement parts.
Sizing considerations
- For 2–3 bathrooms: 7.0–8.4 GPM models typically cover essential simultaneous use.
- For larger homes or high demand: consider higher GPM outdoor models or multiple units with proper load calculations.
Installation and safety considerations
- Professional installation is recommended for gas line connections and venting requirements.
- Ensure proper clearance, vent sizing, and compliance with local codes.
- Outdoor units require weather protection and secure mounting.
Energy and cost considerations
- Tankless systems reduce standby energy loss compared to traditional tanks, potentially lowering utility bills.
- Initial costs are higher than tank heaters, but ongoing savings and space benefits can offset the investment over time.
Quick comparison at a glance
- Best for indoor install: Rheem RTG Series 7.0 GPM Natural Gas Indoor — compact and versatile for interior spaces.
- Best for high flow outdoors: Rheem RTG Series 8.4 GPM Natural Gas Outdoor — top flow for multi‑bath homes.
- Best for propane setups: Rheem RTG Series 7.0 GPM Liquid Propane Outdoor — reliable outdoor propane option.
- Best for outdoor multi‑point: Outdoor 7.0 GPM Natural Gas models — two listings provide flexible outdoor options.
FAQ
- What is a non‑tank water heater? A non‑tank water heater, or tankless water heater, heats water on demand without storing hot water in a tank.
- Do I need venting for gas tankless heaters? Most natural gas units require venting when installed indoors. Outdoor units bypass indoor venting.
- Which is better, gas or propane tankless? Both can provide strong performance. Choose based on available fuel supply and installation constraints.
- Can tankless heaters supply hot water for multiple bathrooms? Yes, but sizing is crucial. Higher GPM models better handle higher simultaneous demand.
- Are outdoor tankless heaters weatherproof? Outdoor units are designed for exterior use but may require weather protection and periodic maintenance.
- Is maintenance required? Yes, regular service checks help maintain efficiency and prevent mineral buildup in gas units.