Answering the question about indoor or outdoor tankless water heaters, these selections cover both installation styles and family sizes. Outdoor models are ideal for vent-free setups and easier weatherproofing, while indoor units suit spaces with dedicated utility rooms. This guide highlights five practical choices, focusing on reliability, installation flexibility, and energy efficiency. The top picks are best for large households, busy multi-bath homes, and users who value smart control or app-based monitoring.
| Product | Best For | Installation | Approx. Output |
|---|---|---|---|
| Rheem RTG Series | Large families, multiple showers | Outdoor | 180,000 BTU/hr |
| MIZUDO 120k BTU Indoor/Outdoor | Smart control enthusiasts | Indoor/Outdoor | 5.1 GPM |
| MIZUDO Propane 120k BTU | Outdoor flexibility | Indoor/Outdoor | 5.1 GPM |
| MIZUDO 199k BTU Indoor | Medium to large homes | Indoor | Up to 10.3 GPM |
| Baococo 18L Propane | Travel, RV, outdoor use | Outdoor | 4.76 GPM |
Rheem RTG Series Outdoor Tankless Water Heater
- High-performance natural gas tankless unit delivering endless hot water on demand for whole-house use.
- Provides 8.4 GPM at a 35°F temperature rise, with 180,000 BTU/hr output for 3–4 simultaneous showers.
- Energy-efficient non-condensing model with a 0.82 Uniform Energy Factor (UEF).
- Outdoor installation eliminates venting needs and simplifies setup.
- Durable metal cabinet and wall-mount design for outdoor spaces.
Best for large households seeking reliable, high-volume hot water without indoor venting concerns. Choose this if you need outdoor installation to minimize indoor space usage. Caution: outdoor units require weatherproofing and protection from extreme temperatures.
MIZUDO 120,000 BTU Indoor/Outdoor Tankless Water Heater
- Flexible installation supports indoor or outdoor use with optional accessory kits.
- Smart WiFi and app control for remote temperature management and energy monitoring.
- Advanced temperature stability with precise control to maintain water within 1°F during simultaneous use.
- Designed for versatile homes and space configurations.
- Best for tech-savvy homeowners who want remote management and flexible placement.
Best for households needing installation flexibility and remote control features. Choose this if you value app-based management. Limitation: conversion kits may be required for strict indoor installations, adding setup steps.
MIZUDO 120,000 BTU Propane Tankless Water Heater
- Indoor/outdoor installation flexibility with outdoor conversion options.
- Smart WiFi and app control for remote operation and energy tracking.
- Advanced flow monitoring and gas modulation maintain stable output during multi-fixture use.
- Ideal for homes needing versatile placement and propane availability.
- Consider propane pricing and supply when planning long-term use.
Best for homeowners who prefer propane with placement flexibility. Opt for this if outdoor placement is a priority, but be mindful of propane availability and outdoor weather protection.
MIZUDO Natural Gas Tankless Water Heater, 199,000 BTU
- Up to 10.3 GPM whole-house hot water capability, suitable for 2–3 bathrooms plus utilities.
- ±1°F precise temperature control with a broad 107°F–149°F adjustable range.
- Low-flow activation at 0.53 GPM supports efficient on-demand heating.
- Strong gas modulation maintains steady temperatures during peak usage.
- Best for mid-to-large homes needing higher flow rates without electric storage tanks.
Best for busy homes with multiple fixtures needing reliable, consistent hot water. Choose this if you require high output and precise control. Limitation: higher BTU input may require robust gas supply and venting considerations.
Baococo 18L Tankless Water Heater (Propane)
- Compact, portable propane unit designed for camping, RV, outdoor use, or small spaces.
- 4.76 GPM flow rate with a maximum 115,425 BTU/hour heating power.
- Temperature range from 17°F to 113°F with a 4.76 GPM continuous hot water flow.
- Six protections including overheat, dry combustion prevention, and flame failure cutoff for safety.
- Better for travel and outdoor activities than for whole-house residential use.
Best for outdoor adventures or temporary setups where mobility matters. Choose this if you need a lightweight, travel-friendly option. Caution: not designed to replace a full-home water heating system.
Buying Guide: Key Considerations For Indoor Or Outdoor Tankless Water Heaters
How to pick the right model depends on fuel type, installation location, and hot water demand. Start by estimating peak GPM needs for your home and compare with unit outputs. Consider whether you want indoor or outdoor installation based on space, venting, and climate.
What fuel type suits your home?
Natural gas units are common for higher flows, with non-condensing and condensing options. Propane is a flexible alternative when natural gas isn’t available. Indoor installations may require proper venting and clearance; outdoor units avoid venting but need weather protection.
How much hot water do you actually need?
- Smaller homes or apartments: 3–4 GPM could be enough for a shower and sink.
- Medium homes with 2–3 bathrooms: 6–8 GPM often works well.
- Large homes with multiple simultaneous uses: look for 8–10+ GPM or higher, depending on climate.
Smart features and app control: worth it?
WiFi-enabled models enable remote temperature adjustments, energy monitoring, and maintenance alerts. This can help optimize efficiency and simplify service planning.
Installation and space considerations
- Outdoor units should be weatherproofed and sheltered from harsh conditions.
- Indoor units require proper venting, clearance, and safe access for service.
- Electrical and gas supply capacity should be evaluated by a qualified installer.
Frequently Asked Questions
- Can I install a tankless water heater outdoors?
- What does GPM tell me?
- Do tankless heaters use less energy?
- Is WiFi control necessary?
- How do I know which size to choose?
- Are there safety concerns with gas tankless heaters?
Yes, outdoor units are designed for weather-exposed spaces, but they require protection from the elements and proper mounting.
GPM indicates the maximum water flow rate the unit can provide at a specific temperature rise. Higher GPM suits busier homes.
On-demand units typically save energy by heating water only when needed, reducing standby losses compared with storage tanks.
Smart control is optional but can improve convenience, monitoring, and scheduling for energy savings.
Estimate peak simultaneous hot water usage (showers, sinks, appliances) and select a unit with sufficient GPM to meet that demand.
Follow manufacturer installation instructions and have a licensed professional handle gas connections, venting (if applicable), and clearance requirements.