By Graham SheridanChoosing the best hot water system for off-grid living means balancing three things at once: how much hot water you actually use, how much sun or other energy your site can reliably provide, and how the system fits into a home that may have no grid connection, limited roof space and a water source that is a well, cistern or spring. Off-grid users often end up with a system that is oversized for the rest of their setup, or one that quietly depends on a backup heater they forgot to plan for. This article compares six options and explains the selection criteria we used: manufacturer specifications, brand reputation for off-grid and remote installations, and the patterns owners tend to describe in feedback. We did not test these products ourselves. Each recommendation is based on published specifications and reported owner experience, and every system should be sized against your own water demand, pressure and climate before purchase.
Our Top Picks
Quick Comparison
| Product | Best for | Key feature |
|---|---|---|
| Solar Shower Bag (camp-style solar shower) | Occasional use, cabins, weekend sites | No electricity, no plumbing required |
| Rheem Solar Thermal Collector Kit (flat-plate, with storage tank) | Full-time households with moderate hot water use | Passive or pumped loop with stored volume |
| SunPower-compatible solar thermal evacuated tube systems | Cold climates and low-sun winter months | Evacuated tubes that retain heat in cold air |
| SolarEdge-ready PV-driven electric water heater (diverter setup) | Sites with a robust PV array and battery bank | Uses surplus PV power, no fossil fuel |
| Eccotemp L5 tankless propane water heater | Remote cabins with propane supply | Tankless, on-demand hot water |
| Rinnai RU199iN tankless gas water heater | Larger households with a propane or natural gas supply | High flow rate for simultaneous fixtures |
Solar Shower Bag (camp-style solar shower)
This is the simplest option for people who only need warm water a few times a week, such as weekend cabins, hunting camps or shared remote sites. It needs no plumbing and no electricity, and it works wherever the sun reaches a dark bag.
Key specs
- Typical capacity: about 5 to 20 liters, depending on model
- Dark PVC or similar bag with a hose and on/off valve
- Requires hanging in direct sun for several hours to heat
- Gravity-fed; pressure depends on how high the bag is hung
Pros
- No installation and no moving parts
- Very low maintenance
- Works in any location with direct sun
Cons
- Limited volume and temperature; poor for multi-person daily use
- Output drops sharply on cloudy days and in winter
Rheem Solar Thermal Collector Kit (flat-plate, with storage tank)
This suits a full-time household that wants a conventional, plumbed hot water system and can dedicate roof or ground space to a flat-plate collector. Rheem is a long-established US water heater manufacturer with a solar line, which makes parts and local service easier to find than with many smaller imports.
Key specs
- Flat-plate collector with an insulated storage tank
- Designed for active (pumped) or passive loops depending on configuration
- Requires an adequate collector area sized to daily hot water demand
- Typically paired with a backup heater for cloudy periods
Pros
- Established brand with recognizable parts and service network
- Storage tank provides buffer for evening use
- Scales to larger households with added collectors
Cons
- Needs a pump and controller in active configurations, which draws power
- Requires a backup heater in winter or extended cloudy spells
SunPower-compatible solar thermal evacuated tube systems
Evacuated tube collectors perform better than flat-plate designs in cold weather and diffuse light, which makes them a common choice for off-grid sites at higher latitudes or elevations. Owners in cold climates often describe them as more forgiving in shoulder seasons, though output still falls in deep winter.
Key specs
- Glass evacuated tubes with absorber fins
- Typically sold as a collector array feeding a storage tank
- Efficiency is less sensitive to ambient air temperature than flat-plate designs
- Check tube count and total aperture area against your target daily volume
Pros
- Strong performance in cold and overcast conditions
- Modular: tubes can be added or replaced individually
- Suits sites with limited south-facing roof space when mounted on frames
Cons
- Glass tubes are more fragile in hail-prone areas
- Higher stagnation temperatures require careful pressure and freeze protection
SolarEdge-ready PV-driven electric water heater (diverter setup)
For off-grid homes that already have a substantial PV array and battery bank, an electric water heater fed by surplus PV through a diverter can avoid a separate solar thermal loop. This route makes most sense when the PV system is oversized for everything else, because the heater will draw whatever surplus is available.
Key specs
- Resistive element heater controlled by a PV surplus diverter
- Requires an inverter or controller compatible with the diverter logic
- Output depends on PV surplus and battery state of charge
- Tank size should match daily volume and recovery time
Pros
- Uses existing PV without a second collector loop
- No fuel deliveries or combustion appliances
- Can prioritize hot water only when the battery is full
Cons
- Performance depends entirely on PV sizing and battery health
- Diverter and inverter compatibility must be confirmed before installation; consult a qualified electrician or solar installer
Eccotemp L5 tankless propane water heater
A tankless propane unit is a practical backup or primary option for remote cabins where propane is delivered and the solar supply is seasonal. It heats water on demand, so there is no standby loss from a tank.
Key specs
- Propane-fired tankless design
- Designed for low-flow, point-of-use or small-household use
- Requires a minimum water pressure and a proper vent for combustion air and exhaust
- Check the unit’s rated temperature rise and flow rate at your local inlet temperature
Pros
- Compact and well suited to small cabins
- On-demand heating eliminates tank standby losses
- Low upfront complexity compared with multi-loop solar systems
Cons
- Requires a propane supply and a safe venting path
- Flow drops noticeably if inlet water is very cold, common in well-fed systems in winter
Rinnai RU199iN tankless gas water heater
For larger off-grid households with propane or a natural gas supply, a higher-capacity tankless unit can serve more than one fixture at once. Owners often describe its flow rate as the main reason for choosing it over smaller units.
Key specs
- Tankless gas water heater with high rated flow
- Designed for whole-house or multi-fixture use
- Requires adequate gas line sizing and combustion air supply
- Check minimum activation flow and temperature rise against your well or cistern supply
Pros
- Higher flow rate for simultaneous showers and sinks
- Continuous hot water without tank depletion
- Widely serviced and documented by the manufacturer
Cons
- Higher fuel demand than small point-of-use units
- Gas line and venting work should be done by a licensed installer
Buying Guide
Selection criteria for off-grid hot water
Start with daily volume, not product features. A household of two using a 7-minute shower twice a day needs a very different system from a family of five with a dishwasher. Measure or estimate hot water use in liters per day, then add a margin for winter and cloudy periods. Next, check your water supply: well pumps have limited flow and pressure, and cold inlet water in winter reduces the temperature rise a tankless unit can deliver. Finally, consider your energy budget. A solar thermal system needs sun, a PV-driven heater needs surplus generation, and a propane unit needs fuel deliveries. The best hot water system for off-grid living is usually the one whose energy source matches what your site produces most reliably.
Important features to compare
- Flow rate (gallons or liters per minute): Match the heater’s rated flow to the number of fixtures you run at once.
- Temperature rise: The difference between inlet water temperature and outlet temperature. Tankless units are rated at a specific rise; winter inlet temperatures lower actual output.
- Head height: For gravity or low-pressure systems, the vertical distance from the storage tank or bag to the outlet determines pressure. A few feet of head can be enough for a camp shower and not nearly enough for a multi-fixture home.
- Storage volume and recovery time: Tanks buffer demand. Recovery time tells you how long the tank takes to reheat after heavy use.
- Freeze protection: Outdoor collectors and exposed pipes need a freeze strategy, such as drain-back, glycol loops or insulation.
Specs to check before you buy
- Rated collector area or heating capacity
- Maximum operating pressure and minimum activation flow
- Required electrical input for pumps or controllers
- Venting and combustion air requirements for gas or propane units
- Warranty terms and whether the manufacturer has a service network near you
Choosing by need
- Occasional use or a weekend cabin: A solar shower bag is usually enough.
- Full-time, small household, sunny site: A flat-plate solar thermal kit with a storage tank.
- Cold climate or long winters: Evacuated tube collectors with a backup heater.
- Large PV array and battery bank: A PV-diverted electric heater, if the electrical design supports it.
- Remote cabin with propane delivery: A small tankless propane unit.
- Larger household with simultaneous showers: A higher-flow tankless gas unit.
Things to watch out for
- Undersizing the collector or tank for winter demand, which leads to constant reliance on backup heat.
- Ignoring cold inlet temperatures, which reduce tankless output more than most buyers expect.
- Installing gas or propane appliances without proper venting; this is a safety issue, and a licensed professional should handle it.
- Overlooking pressure. Gravity-fed systems and well pumps behave differently, and head height matters.
- Skipping freeze protection on any exposed collector or line in a cold climate.
For guidance on system layout and how collectors, tanks and pumps interact, see Solar Water Heater Components: Collectors, Tanks, Pumps and Pipes and Sizing a Solar Water Heater for Your Household’s Hot Water Demand.
FAQ
What is the best hot water system for off-grid living in a cold climate?
In cold climates, evacuated tube solar thermal collectors generally perform better than flat-plate designs because they lose less heat to ambient air. Most cold-climate off-grid systems still need a backup heater for deep winter, and the storage tank should be well insulated. A propane tankless unit is another common choice when solar output drops sharply.
How much hot water can a solar shower bag provide?
Most camp-style bags hold roughly 5 to 20 liters. Output depends on sun exposure, bag height and ambient temperature. It works well for one or two short showers per day in good sun, and poorly in overcast or winter conditions.
Does a tankless water heater work with a well pump?
Yes, but check the unit’s minimum activation flow and pressure requirements against your pump’s output. Well pumps often have limited flow, and tankless units need enough flow to trigger the burner. Cold winter inlet water also reduces the temperature rise, so confirm the rated output at your local inlet temperature.
How do I size a hot water system for an off-grid home?
Estimate daily hot water use in liters, add a margin for winter, and then match collector area or heater capacity to that volume. A plumbing or solar professional can run a load calculation based on your local solar resource. For detailed steps, see Sizing a Solar Water Heater for Your Household’s Hot Water Demand.
Can I use surplus PV power to heat water?
Yes. A PV diverter sends surplus electricity to a resistive water heater element when the battery is full or the array is producing more than the household uses. Performance depends on PV sizing and battery state of charge. Electrical compatibility and wiring should be reviewed by a qualified electrician or installer.
Do I need a backup heater for solar hot water off-grid?
In most locations, yes. Solar thermal systems can run out of heat on cloudy days and during winter. A backup propane, electric or wood-fired source is common. Settings and control logic are covered in Backup Water Heating for Solar Systems: Options and Settings.
How often does an off-grid hot water system need maintenance?
Solar thermal systems typically need seasonal checks of fluid levels, pressure, insulation and freeze protection, plus periodic cleaning of collector glass. Tankless gas or propane units need annual inspection of burners, venting and scale buildup, especially with hard water. Follow the manufacturer’s schedule and consider a professional service visit.
Is a propane tankless heater a good fit for a remote cabin?
It can be, especially if the cabin is small, propane delivery is reliable and the water supply has adequate flow and pressure. Confirm venting requirements and winter inlet temperatures before buying, and have a licensed professional install gas or propane equipment.
Conclusion
The best hot water system for off-grid living depends on how much water you use, what energy you can reliably produce and how your water supply behaves in winter. For occasional use, a solar shower bag keeps things simple. A flat-plate solar thermal kit suits a full-time small household with good sun, while evacuated tubes are the stronger choice in cold climates. A PV-diverted electric heater makes sense when your solar array and battery bank are already oversized, and tankless propane or gas units work well for cabins and larger households that have a dependable fuel supply. Whichever route you choose, size the system against your own daily demand and winter conditions, plan a backup source, and have any gas, propane or electrical work done by a qualified professional.
Related reading
- 7 Best Solar Water Heating Large Household Systems Compareds (2026)
- Types of Solar Water Heating Systems: Active, Passive, Direct, Indirect
About Graham Sheridan
Graham puts together our solar water systems guides, digging through specifications, manufacturer details and owner reviews so you don't have to.
