Best Gas Tankless Heaters for Hot Tubs and Outdoor Baths
If you need instant hot water on the go, a gas tankless heater is a strong choice. This guide highlights five reliable options that deliver on-demand heat for hot tubs, spa baths, and outdoor showers. Best for campers, RVers, cabins, and off-grid setups, these units prioritize portability, quick heat, and safety protections. Read on to compare features, suitability, and any limitations so you can choose the right model for your outdoor hot water needs.
Quick comparison table of selected products:
| Product | Best For | Key Benefit |
|---|---|---|
| forimo 5.26GPM Tankless Propane Water Heater | Camping, RVs, boats | High output and compact design |
| Outdoor Propane Tankless Water Heater 6L | Boats, cabins, cabins | 6L flow with 40,000 BTU/hr |
| Tankless Propane Water Heater 5.26GPM | Camping, remote baths | Digital display, multi-protection |
| Glonerle SUPA Water Heater | Outdoor spas, portable hot tubs | High-output propane heating |
| MIZUDO Natural Gas Tankless Water Heater | Big homes, multiple showers | Up to 5.1 GPM, constant temp |
forimo Tankless Propane Water Heater – 5.26 GPM
Best for: Campers and RV users seeking a compact, high-flow propane heater. This unit outputs up to 5.26 GPM with a maximum temperature rise of 167°F, suitable for fast hot showers in outdoor settings. It uses CSA-approved protections, flame-failure devices, anti-freeze, and overheat safeguards. Pitfalls: requires propane LPG and relies on a water pressure of about 3.6 PSI to activate flow.
- Output: 68,000 BTU/hour maximum
- Protection: flame failure, anti-freeze, overheats
- Power: propane fuel; battery-powered ignition
Outdoor Propane Tankless Water Heater – 6L
Best for: RV trips, cabins, and boats needing reliable instant hot water with a compact footprint. It delivers up to 40,000 BTU/hour and about 1.58 GPM at 1.58 GPM flow, starting at low water pressure. Consider this if you prioritize portability and straightforward installation. Caution: ensure the regulator and hose compatibility for your setup.
- Compact size: 11.8″ x 5.3″ x 17.3″, 12 lb
- Includes: gas regulator, hoses, and installation hardware
- Protection: overheat, low water, dry combustion, anti-freeze
forimo Tankless Propane Water Heater – 5.26GPM (Digital Display)
Best for: Outdoor enthusiasts who want a digital display and solid protections. This model also supports 3.6 PSI water pressure and can deliver 5.26 gallons per minute with a 167°F max rise. It shares CSA-approved regulators and flame-failure protections. Limitation: propane-specific, so not suitable for natural gas lines.
- Digital display for easy temp control
- Same 68,000 BTU/hour capacity as other forimo unit
- Propane-only operation
Glonerle SUPA Water Heater – Portable Propane Spa Heater
Best for: Portable spas and outdoor hot tubs where mobility is key. It’s designed to heat spa water rapidly with a high output (approx. 105,776 BTU/h). The unit includes wheels and a direct connection option to an outdoor faucet, making hot water on demand possible at campsites or parks. Caution: ensure spa capacity aligns with heater capacity to avoid under-heating larger volumes.
- High-output propane heating
- Two large wheels for mobility
- Smart temperature control with auto shutoff
MIZUDO Natural Gas Tankless Water Heater – Gen 2
Best for: Big homes or properties requiring simultaneous hot water for multiple showers. This unit delivers up to 5.1 GPM with 120,000 BTU and uses gas modulation to maintain a constant temperature with minimal fluctuation. It’s UL-listed and CSA-certified and supports two to three showers concurrently. Caution: installation should follow safety codes to maintain venting and gas line requirements.
- Up to 5.1 GPM at 120,000 BTU
- Constant temperature within ±1°F
- UL and CSA certified; 2-year unit, 5-year heat exchanger support
Buying Guide: Gas Tankless Heaters For Hot Tubs And Outdoor Baths
What should I consider before buying?
Gas tankless heaters differ in fuel type ( propane vs natural gas), flow rate (GPM), and heat output (BTU). For hot tubs, prioritize models that deliver enough GPM to maintain consistent water temperature, even with multiple outlets. Portability matters for camping or RV use, while larger homes may require higher GPM and multi-shower capabilities.
Which features impact performance?
- BTU rating and flow rate (GPM): This determines how quickly hot water arrives and how many fixtures can run simultaneously.
- Temperature rise: The maximum temperature increase the unit can achieve at a given flow; higher rise means hotter water at the same flow.
- Protections: Flame failure, anti-freeze, overheating, dry-fire protection, and low-water start are essential for safety in remote or mobile setups.
- Portability: Look for compact designs, integrated handles, and battery-powered ignition if you plan to move the unit often.
- Fuel type and fuel availability: Propane is portable but requires tanks; natural gas is convenient if a gas line is accessible.
Where is a gas tankless heater best used?
Best uses include outdoor showers, RV or boat setups, cabins, remote campsites, and hot tubs where continuous hot water is needed without a storage tank. For high-demand households or larger pools, a unit with higher GPM and robust modulation is advantageous.
Care and maintenance considerations
Regularly inspect gas connections, regulators, and venting per local codes. Ensure safe clearance around the heater and adequate ventilation. Use only certified parts and follow manufacturer guidelines for winterization and storage when not in use.
What if I have a large hot tub or multiple zones?
Choose a unit with higher GPM (5–6 GPM or more) and robust BTU output. For homes with several showers, select a heater with a higher flow rating or consider pairing with a secondary unit for load balancing.
Safety and installation basics
Follow all local gas codes and installation instructions. Use CSA or UL listed components and have a licensed technician install gas line connections and venting when required. Ensure seizure protections and flame safeguard devices are functional.
FAQ
- What is the typical GPM needed for a hot tub?
- Can these heaters run on propane or natural gas?
- Do I need a tank or tankless system for outdoor showers?
- Are these heaters safe for use in camping scenarios?
- What maintenance is required?
Most hot tubs require around 3–5 GPM to maintain a comfortable temperature, depending on tub size and desired rise.
Most models in this list are propane-specific; the MIZUDO unit uses natural gas. Check the fuel source before purchase to match your setup.
Tankless systems are ideal for outdoor showers due to continuous hot water and compact form factors, as long as a suitable gas supply and venting exist.
Yes, models with flame-failure protection, anti-freeze, and overheating protections are designed for outdoor use in camping and remote locations.
Regular inspection of gas fittings, regulators, and venting is recommended. Clean and check filters as instructed by the manufacturer.