The best outdoor electric tankless water heater balances weatherproof build, strong flow, and smart safety.
Picture this: you step outside to rinse sandy feet, spray down muddy gear, or jump into a backyard shower after a pool day. You turn the handle and wait… and wait. Cold water dribbles out. That is where the best outdoor electric tankless water heater wins the day. It gives hot water on demand, without a bulky tank or a messy vent. It saves space and slashes standby energy loss. It can even live closer to where you use water. In this guide, I break down top picks, real-life pros and cons, and simple tips to help you buy with confidence.
Rheem 18kW Electric Tankless (240V)
The Rheem 18kW 240V is a compact electric tankless unit with serious punch for its size. It uses self-modulating power to match output to demand. That helps reduce waste and smooth out temperature swings. For small homes, cabins, pool houses, or a dedicated outdoor shower with moderate flow needs, this unit can be a sweet spot.
While Rheem designs this model for indoor installs, many homeowners place it in a weatherproof cabinet outdoors. That keeps the unit safe from rain and sun. It also shortens your hot water runs to outdoor fixtures. Always confirm local code, use GFCI protection, and add freeze mitigation if you live in cold zones.
Pros:
- Reliable brand with strong service network and clear manuals
- Self-modulating control trims power use and steady temps
- Digital temperature setting for quick, precise adjustments
- Compact form fits tight spaces and utility enclosures
- Great for single-bath or outdoor shower setups in mild climates
- No venting needed; install flexibility vs. gas units
- Quiet operation suits patio or pool areas
Cons:
- Not an outdoor-rated housing; needs a weatherproof box
- 18kW may be light for cold climates or multi-fixture use
- Requires two 40A breakers and 8 AWG wiring; pro install advised
My Recommendation
If you need hot water close to where you use it, and your climate is mild, the Rheem 18kW is a smart, simple pick. It is easy to live with, and it sips power compared to old tanks. For the best outdoor electric tankless water heater use case, mount it in a sealed, ventilated, and code-compliant cabinet near an outdoor shower or sink.
| Best for | Why |
| Outdoor showers in mild climates | Good flow for one fixture, no venting, compact size |
| Small homes or studios | Self-modulation, simple controls, easy maintenance |
| Pool house or backyard sink | Quiet, efficient, and close-to-tap installation |
Rheem RTEX-24 24kW Electric Tankless
The Rheem RTEX-24 steps up to 24kW, which boosts flow and rise. It can serve a shower and a sink at once in warm to moderate climates. The digital thermostat and robust self-modulating tech keep temps rock steady. If you want a proven brand and a bit more muscle, this model hits a great balance.
Like the 18kW, the RTEX-24 is made for indoor mounting. For outdoor service, many owners house it in a NEMA-rated cabinet with drainage and airflow. Add heat tape on exposed pipes and a freeze sensor if your winters dip low. Done right, it can act like the best outdoor electric tankless water heater for a patio bath, guest casita, or workshop sink line.
Pros:
- Higher output than 18kW for two low-flow fixtures
- Stable temperature control with digital precision
- Strong brand backing and common parts
- Compact footprint for tight utility spaces
- No combustion or venting; easier compliance in many areas
- Efficient for intermittent use near outdoor points
- Clear service access and replaceable elements
Cons:
- Requires three 40A breakers and 8 AWG wiring in many setups
- Still not a true outdoor-rated chassis; needs a protective enclosure
- Cold climates may still overtax it with high flow demands
My Recommendation
Choose the RTEX-24 when you want electric ease with extra headroom. It is a better fit for a pool shower plus hand sink at the same time. If you seek the best outdoor electric tankless water heater for a warm-climate yard or cabana, this one deserves a serious look with a proper weatherproof cabinet.
| Best for | Why |
| Warm-climate two-fixture use | 24kW handles shower + sink at modest flows |
| Backyard casita or guest suite | Stable temps and easy controls for daily use |
| Retrofits from old small tanks | Space saver and no standby losses |
APUS 190k BTU Outdoor Tankless (NG, 8.1 GPM)
This APUS unit is not electric. It is a natural gas, outdoor-rated tankless with up to 8.1 GPM. That is enough for two to three showers at once in many homes. It includes WiFi and a remote for easy temp tweaks. If you are open to gas, outdoor models like this shine for high-demand families.
Because it mounts outdoors, you skip indoor vent runs. That frees space and cuts install steps. Combustion safety is built in with modern sensors. The trade-off is you need a gas line sized for 190,000 BTU and proper clearances.
Pros:
- Outdoor-rated chassis; no separate cabinet needed
- High flow for multi-bath homes or busy yards
- WiFi and remote control for convenience
- Great for cold inlet temps when you need strong rise
- Free up indoor space; no indoor venting
- Faster whole-home hot water than most electric units
- Designed for weather exposure with proper install
Cons:
- Not electric; needs natural gas supply and gas-safe install
- Annual maintenance and descaling recommended
- Noise is higher than electric units, though outdoors
My Recommendation
If you only want electric, skip this. If gas is fine and you want outdoor, this is a value workhorse. Families who use the yard a lot love the capacity. While it is not the best outdoor electric tankless water heater by definition, it is a top outdoor tankless pick for high flow and simple placement.
| Best for | Why |
| Large households | 8.1 GPM supports multiple showers at once |
| Cold climates | High BTU input delivers strong temperature rise |
| Outdoor-only placements | Outdoor-rated unit reduces vent and space needs |
110V 3.5kW Electric Tankless (LED, Black)
This 110V, 0–3500W unit is tiny and simple. It runs on a standard household circuit in many cases, though a dedicated line is safer. It is best as a point-of-use heater for one low-flow sink. The LED display makes it easy to set and monitor temperature.
It is sometimes shown for “indoor or outdoor” use. In practice, 3.5kW is too small for showers unless your inlet is very warm and your flow is very low. Think of it as a helper for an outdoor hand-wash station or a remote bar sink. If you want the best outdoor electric tankless water heater for showers, choose a higher kW model.
Pros:
- Very compact and lightweight for tight spots
- Low power draw vs. 240V units
- Simple controls with clear LED display
- Great for a single low-flow faucet
- Budget-friendly entry into tankless convenience
- Fast install for point-of-use near the tap
- Reduces wait time and water waste for quick tasks
Cons:
- Not enough power for most showers, especially in cold water
- Questionable outdoor durability; needs full weatherproofing
- Limited temperature rise; seasonal in cooler regions
My Recommendation
Use this for a single outdoor sink or a tiny cabin in a warm area. It is not a whole-house or shower solution. If you are hunting the best outdoor electric tankless water heater, this is a niche pick for very light-duty tasks with short piping and warm inlet temps.
| Best for | Why |
| Outdoor bar sink | Low flow, quick heat, tiny footprint |
| Backyard hand-wash station | Improves hygiene without big power needs |
| Warm-climate RV or shed sink | Works on 110V with modest rise needs |
Rheem RTG-70XLN-3 Outdoor Tankless (NG, 7.0 GPM)
This Rheem is an outdoor, non-condensing natural gas unit. It delivers about 7.0 GPM, which suits small to mid-size homes. The “XLN” line is built to live outside with the right clearances. No indoor venting or large utility space needed.
It is not electric, but it solves the same problem: hot water close to where you use it. The brand support and reliability are strong. If you have gas service and want an outdoor mount that just works, this is a safe bet. It beats most electric units for cold-climate rise and whole-home demand.
Pros:
- Outdoor-rated; clean, space-saving install
- Strong flow for one to two showers plus sinks
- Trusted brand with service parts and support
- No indoor vent or combustion air plan to manage
- Good balance of price and performance
- Tested safety features and diagnostics
- Solid choice for cabin, ADU, or backyard build
Cons:
- Not electric; needs a gas line and proper regulator
- Annual flush and upkeep for best life
- Outdoor placement must follow clearance charts
My Recommendation
If you want a simple outdoor gas tankless that covers most families, this Rheem is a standout. For pure electric seekers, look to 18–27kW units and a proper cabinet. When I help folks weigh the best outdoor electric tankless water heater versus gas, I point to climate, flow needs, and service access. Match those, and you will be happy long term.
| Best for | Why |
| Small to mid-size homes | 7.0 GPM covers typical daily use |
| New builds with gas | Outdoor mount saves indoor space and vent cost |
| Cold inlets | More rise than most electric options |
FAQs Of best outdoor electric tankless water heater
Are there true “outdoor-rated” electric tankless units?
They are rare. Most electric tankless models are indoor-rated. Many owners use a weatherproof, ventilated cabinet to protect them outdoors. Always follow code and manufacturer guidance.
What size electric tankless do I need for an outdoor shower?
In warm climates, 18–24kW can work for a single shower. In colder areas, consider 24–36kW if your panel allows. Lower kW works only with very low flow heads and warm inlet water.
Can I install an electric tankless outdoors without a cabinet?
I do not recommend it. Use a NEMA-rated enclosure, GFCI protection, and freeze protection where needed. Keep clear airflow to avoid overheating.
Is electric or gas better for outdoor tankless?
It depends. Electric is simple and quiet, with no venting. Gas delivers higher flow and rise, which helps in cold climates. Pick based on your power panel, gas access, and demand.
How do I winterize an outdoor electric tankless?
Shut power. Drain the unit per manual. Blow out lines if needed. Use heat tape on exposed pipes. Some regions require full seasonal drain-down.
Final Verdict: Which Should You Buy?
If you want the best outdoor electric tankless water heater for a shower or sink in mild zones, the Rheem RTEX-24 is my top electric pick. For lighter tasks, the Rheem 18kW is a budget-friendly choice. The 110V 3.5kW is only for a single low-flow faucet.
If gas is on the table and you want outdoor-ready hardware, the Rheem RTG-70XLN-3 is the safer all-rounder, with APUS offering more flow. Match climate, flow, and power to land the best outdoor electric tankless water heater for your space.
