Off Grid On Demand Hot Water Heaters | The Best Options Available | Off Grid Permaculture
On Demand Off Grid Hot Water Heater Tankless Propane

Off Grid On Demand Hot Water Heaters | The Best Options Available

January 12, 2021

Daniel Mark Schwartz Profile Picture

Tankless on-demand hot water heaters are highly efficient appliances suitable for off-grid homesteads. But, there are several pitfalls to watch out for, which on-grid installations don’t have to consider. With many brands choose from, these are the three best makes and models for off-grid hot water heating.

Top On-Demand Hot Water Heaters for Off-Grid Living

Here are my top three choices for off-grid on-demand water heaters, based on the following considerations

  • Efficiency
  • Cost
  • Low electrical usage
  • Safety and Reliability
  • Usability with low water pressure
Camplux 5L thermomate ZERO16 Rinnai RL75eP
Lowest Cost Most Popular High Efficiency
Flow Rate 1.32 GPM 4.23 GPM 7.5 GPM
Efficiency Medium (0.314) High (0.327) Very High (0.375)
Water Pressure 3.0–110 PSI 0.7–138 PSI ~30+ PSI
Location Indoor/Outdoor Outdoor Outdoor
Power 2 “D” Cell 2 “D” Cell 220 VAC
Fuel Propane Propane Propane
Size 20.4" x 11.5" x 4.23" 25.6" x 15.7" x 7.5" 24.3" x 14" x 9.6"
Misc Not Potable Ultra Low Pressure Capable Leak Detection w/ Shutoff
Cost See Price See Price See Price

Low Cost On Demand Water Heater Ideal for Tiny Homes & Yurts

For small installations like tiny houses, off-grid RVs, and yurts, I highly recommend a smaller, portable Camplux water heater like the one listed above. These heaters offer outstanding efficiency for their size. They work great in low-pressure wells. And, they only require 2 “D” cells, meaning they won’t accidentally drain your primary batteries.

Camplux heaters are not designed to heat drinking water and probably work best as a designated shower water heater installed right in the bathroom. They even come with a shower head in the box. In this case, I would recommend heating water for food or washing dishes on the stove or over a wood fire. Manually heating water also helps you conserve hot water and save on propane, since you know exactly how much you are using each time.

Best Low Pressure On Demand Hot Water Heater

Medium-sized installations should go with the Thermomate, which will is the most popular option on the list. This high-efficiency water heater has similar features to the Camplux — small size, low pressure capable, runs on two “D” cells — however, it can produce more than three times as much water.

This tankless water heater will supply hot water to multiple family members using showers and sinks at the same time. It is also the lowest pressure capable tankless water heater I have ever seen, which is excellent for gravity-fed water systems and high-efficiency water pumps often found in solar-powered well installations

Most Efficient and Reliable On-Demand Hot Water Heater

For families or use on a commercial farmstead, go with the Rinnai. Rinnai is the most popular brand recommended by real homesteaders (see “Most Popular Off-Grid Water Heater Brand” below).

Additionally, the Rinnai is the most efficient water heater on this list and one of the most efficient on the market. Rinnai also makes even more efficient models than the one linked above, but the additional cost for what you get isn’t worth it unless you need to save gas at any cost.

If you are ready to invest in a rock-solid, “lifetime” water heater, then Rinnai is your choice.

Things to Watch Out For When Buying an Off-Grid Water Heater

For those considering a tankless hot water heater for off-grid installation, you are probably aware of the fact that tankless water heaters are the most efficient on the market, and can produce an endless amount of hot water. Efficiency is a major selling point, as it saves in cost and reduces the number of trips to town for a propane refill.

Here are three things you need to watch out for when installing a tankless water heater off the grid, which most people won’t consider.

Limit Energy Usage

Some on-demand hot water heaters are energy hogs. Especially exterior units that use electricity to prevent its water from freezing.

Using energy to heat is seldom a good idea for off-grid homes unless money is no object. Gas or wood-heated appliances are generally the most cost-effective options on the homestead.

By choosing on-demand water heaters that run off batteries, rather than plugging into the wall, we can be certain our water heater won’t drain our whole house batteries.

Usability with Low Pressure (Low Head) Water Systems

On-demand hot water generally doesn’t work well with low-pressure water. This can be a problem with high-efficiency DC well pumps, low head gravity fed water systems, or spring-fed off-grid water systems.

Both the Camplux and Thermomate on-demand water heaters I recommend are designed to work fine in extremely low-pressure water systems. And, even if your current off-grid home has plenty of pressure; you still have the option of saving energy in the future by decreasing system pressure and running your well pump less aggressively.

For more details on running a well pump on solar, with high efficiency and low cost options, check out my popular article:

** Low-pressure capable water heaters are also helpful when designing a failure resistant water system.** When you use a typical on-demand water heater, with the low-pressure capability of the water heaters I recommend, you probably will need an electric pump to keep up the pressure.

Even if you prefer to run a pump for high-pressure showers, being able to run the hot water even when the power system is down gives you additional options in an emergency. The two smaller heaters I recommend run on batteries and will function just fine if your energy system isn’t working.

Additionally, low-pressure water heaters using hand-pumped water. Every off-grid water system should have multiple backups for every function, should one break. And, hand well pumps are an essential backup measure.

Runs form Propane

Propane is ideal for heating water off-grid because it is transportable and widely available.

The time and cost of transporting heating gasses will be the most expensive part of running an off-grid on-demand water heater. Unless you happen to have natural gas pipes at your location and consider using it “off-grid,” propane will be your go-to option since it is easiest to get since it is found at many gas stations and convenience stores in remote locations.

See: “How Much Money It Takes to Live Off the Grid | 5 Hidden Costs”

Propane also allows you to switch to or use biogas as an alternate energy source that you can produce for free on the homestead. See the section titled “Completely Off-Grid On-Demand Hot Water with Biogas” below for details.

The most popular off-grid on-demand water heater brand is Rinnai, based on a poll of homesteaders on Facebook. One Rinnai owner named Ray answered —

“Rinnai, hands down. Ours ran 15 years on LP Propane. We just got NG Natural Gas on our road, and paid $85 for an NG burner assembly.”

Another homesteader named Alec said —

“Rinnai is the cream of the crop.”

John said —

“Rinnai. 12 years and not one problem.”

And, according to Diane —

“[I’ve used] Rinnai for 16 years. Not one issue. Fills a two-person jet tub, runs a dishwasher and washing machine. It NEVER runs out of hot water.”

Heating Water with Biogas from a Home-Scale Biogas Digester

Completely Off-Grid On-Demand Hot Water with Biogas

Many people might dispute whether a propane-powered tankless water heater is actually “off the grid,” considering the fact you need to buy propane in town to make it work.

While propane-based tankless water heaters are a popular comprise in terms off cost, ease of use, and grid independence for many homesteaders there may be a way to run, never have to buy propane again — biogas.

What Is Biogas

Biogas is another name for methane produced during the decomposition of organic materials and collected as an energy source. Methane in biogas burns clean like propane or natural gas with no smell.

Production of biogas has a long history. In Germany, farmers have used waste matter in commercial biogas power generation since the Second World War, proving the viability of the technology. On a smaller scale, Biogas has proven popular farms on in the third world and particularly India as means of producing free cooking gas.

Using Biogas to Heat Water

Propane or natural gas appliances can be converted to run off biogas by drilling out the burner holes to a larger diameter. And, by changing out the burner, you can switch between propane and biogas as necessary.

A single large biogas digester should be enough to provide a family with gas for cooking and heating water on a typically sized homestead. Especially if combined with other water heating methods like solar, which may not be as reliable.

Smaller-scale digesters can also be purchased commercially, giving off gridders the option of using biogas as a backup or emergency energy source.

For information on building or purchasing a biogas digester and converting appliances to biogas, see:

Commercial Solar Hot Water Heater

Solar On Demand Hot Water Heaters

Solar on-demand hot water systems are a cost-effective way to supplement traditional tankless water heaters. Solar water heaters can also be used on their own as either a primary water system or as an emergency fallback.

The most efficient solar water heaters heat water directly in the sun, rather than using solar panels and electricity. These are known as thermal solar water heaters.

Benefits. Solar water heaters are quite cheap and are basically free to run. Adding a clear crystal pipe segment to your solar system can help disinfect water via UV exposure.

Drawbacks. Water heated with solar can vary in temperature quite a bit depending on how sunny it is at the moment of use. Sunny days can produce boiling waters, while cloudy days may only get lukewarm water. I prefer using solar water as a pre-heater for a gas on-demand heater, which will even out the temperature and fill any gaps in solar performance.

Commercial Evacuated Tube Solar Water Heaters

Commercial systems are highly efficient because they use double or triple walled evacuated transparent tubes to heat the water. These tubes work like a thermos or triple-paned windows, keeping as much solar energy in the water as possible.

Vacuum insulation increases the range of days that solar water can be used by extending solar effectiveness in the deep winter and on cloudier days.

For my current recommendation for commercial solar water heaters, see:

DIY On Demand Solar Hot Water Heaters

For the frugal homesteader, very low-cost DIY solar thermal water heaters are optional. Generally, these consist of a black hose coiled up in an insulated box with a glass lid. See the above video for detailed instructions for constructing a low-cost solar water heater.

Just like a hose in summer, the sun will heat the water inside as it passes through. The glass lid and insulation, while optional, do a lot to increase the effectiveness of the heater by trapping solar energy inside, like a greenhouse.

These solar heaters can act as an on-demand system on their own but typically only work really well on hot summer days.

Some builders increase these systems’ effectiveness by hooking the panel up to an insulated hot water tank. By allowing more water to be heated in advance, DIY solar water heaters can work well on colder or cloudier days. Typically the water will be circulated with a small electric pump, but with careful positioning water can flow between the panel and storage tank naturally via thermal siphoning, without the need for a pump.

Compost Heated Hot Water

A YouTube subscriber recently introduced me to the “Jean Pain” style composted heated hot water system. Amazingly enough, this French innovator found a way to get steaming hot water from a pile of decomposing organic matter.

Directions for building a Jean Pain style water heater

Such a design’s overall construction costs are probably less than $100. The materials consist of wooden stakes, wire mesh, and about 300’ feet of polyethylene plastic tubing. Assuming you already have organic matter, which every homesteader should have plenty on hand, this plan is extremely cheap.

Wood Heated Hot Water Systems

copper coil for wood fired hot water heater

One popular idea for hot water production on the homestead is the wood-fired water heater. This on-demand style of water heating uses fire to heat water directly.

The copper coil design is easy to do and highly effective. Cooper tubing can be purchased at any home improvement store. Use 1/4" to 1/2" tubing. The trick to bending these tubes into a coil without crushing them closed is to fill them with water and freeze them before attempting to bend.

Having an appropriately sized tub to wrap the coils around makes the final job neater, but a tidy coil isn’t necessary for proper function so long as non of the tube gets crushed.

Once prepared, place the copper tube heat exchanger you built directly over an open fire, or inside a stovepipe or chimney.

For in chimney coils, be sure the coil outer diameter is 1" – 2" narrower than the inside of the chimney, so the hot air has plenty of room to flow around. Place in a lower section of chimney or pipe that can be easily inspected and is less likely to be covered in creosote.

Visually inspect and clean the copper tubing regularly to make sure it isn’t gumming up. While in a well-designed system, frequently cleaning shouldn’t be necessary, but regular checks are a must for the sake of safety.

For wood-heated hot tubs, consider an immersion wood stove. These specially designed heaters sit directly in a tub of water. You build and tend the fire through an opening in the top, while the water is heated through the side and bottom walls.

The simplest way to heat water with wood is in a pot on a wood stove or over a campfire. Those of us living off the grid shouldn’t be shy about heating water the old fashioned way. When heating water takes work, we are conservative about using the resource. And, at least having the equipment on hand and experience to know how to do it effectively means we have a backup option ready at hand should the need arise.

Electric On Demand Hot Water

Electric water heaters are generally not compatible with the off-grid lifestyle. The cost of off-grid solar and wind power too expensive at the current time to make electric heat a viable option when compared to gas and other alternatives listed above.

See “Total Cost Of Off Grid Solar Photovoltaic Systems” for details on pricing an off-grid power system.

However, if you have access to a large quantity of hydroelectric power, then an electric on-demand water heater might be perfect for your situation. Small scale “micro-hydro” installations used by homesteaders are capable of driving 110VAC and 220VAC (and 240VAC power used outside the US in many places).

This means any common electric on-demand water heater will suffice. And, there is little need to worry about low heat water systems in most cases since you can pump the water up to typical home pressures without much difficulty. And, if the electric power fails, you won’t be able to heat water anyway, so losing water pressure at that time won’t have a serious additional impact like it could be with a gas-powered water heater.

How do I make hot water off the grid?

Off-grid water is most often heated over wood stoves, although propane or biogas fueled on-demand water heaters are a convenient and efficient option. Other renewable heating options are thermal solar water heaters, thermal hot water, and compost heated water.

Is hot water on demand worth it?

On-demand hot water heaters are the most reliable and practical option for off-grid hot water. Less efficient tanked water heaters are too expensive to run. Other renewable options like solar, wood-fired, or compost water heaters aren’t always able to produce hot water or require significant tending.


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