The Best Supplier Of Wood Fired Hot Tub Coil -Smartclima

See which popular Wood Fired Hot Tub Coils that the most DIYers choose

The reasons why choose Smartclima coil kit to DIY your hot tub

Smartclima is a leading manufacturer and supplier of wood fired hot tub coil

Smartclima becomes a leading manufacturer and supplier of wood fired hot tub coil in the world, offering high-quality, efficient, and durable solutions for outdoor hot bath since its invention in 2001 .

Using Seamless Stainless Steel Pipe Structure

Smartclima coil is constructed from extruded seamless tubes boasting even wall thickness, enhanced pressure and freeze resistance, complete freedom from leaks and corrosion, and a 20-plus-year outdoor service life.

Using One-Piece Bent Full Coil Design (Weld-Free Construction)

Smartclima coils are fabricated from a single integral tube bent into shape with zero welded connections. This removes corrosion-susceptible weld seams and delivers reliable long-term anti-corrosion performance for outdoor installations.

Using Premium High-Temperature Hoses & Stainless Steel Fittings

Smartclima coil is equipped with heavy-duty industrial silicone heat-resistant hoses matched with high-temperature resistant 304 stainless steel tube fittings, paired with tool-free quick-release clamps. The silicone material resists melting, cracking and embrittlement under extreme high and low temperatures, unlike ordinary rubber hoses which degrade rapidly. It delivers the same long service lifespan as the heating coil.

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In the below guide, from professional view, Smartclima will introduce everything you need to know about wood-fired hot tub with heater coils, including how they work, their benefits, installation tips, and maintenance.

1. What Is a Wood Fired Hot Tub Heater Coil?

A wood-fired hot tub heater coil is an heat exchanger made of a stainless steel tubing coil that transfers heat from wood burning to the water in tub (See above image). It works by circulating water through the coil, which is heated by the fire, providing a natural, energy-efficient way to warm the tub without electricity.

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2. How Does a Wood Fired Hot Tub Heater Coil Work?

Wood-burning hot tub operates solely on the principle of gravity (thermosiphon circulation or natural convection). Water heated flows upwards and flow out of the upper pipes into the tub because the water in the coil pipes is heated by the wood fire in coil, and at the same time,colder water flows in the pipes from the bottom of the tub. As the water heats up,so the water in coil rise up and flow into tub again.Circulates like this way again and again,the water in tub becomes warmer and warmer.

During all procedures,there is no electricity or gas burning in this system, so it is purely natural or 100% off-grid.

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3. Is it worth to invest on Wood-Fired Hot Tub? Benefits of Heater Coils ?

Eco-Friendly

Immerse yourself in nature with a clear conscience. Our wood-fired hot tub is a model of sustainability. It operates entirely off-grid, using renewable wood fuel as its only power source, eliminating reliance on fossil fuels or electricity. The natural combustion process has a minimal carbon footprint, especially when using locally sourced or reclaimed wood. With no chemicals, pumps, or filters required, the water can be repurposed for garden irrigation after use, making your soak a truly green and earth-friendly retreat.

Cost-Effective

A wood-fired hot tub is a remarkably cost-effective investment. Its operation relies on the natural, affordable energy of wood, completely eliminating ongoing electricity costs for heating. There are no complex pumps, filters, or electrical systems to install or power, which also means minimal maintenance expenses. Once the initial purchase is made, your primary cost is simply the firewood, making it an economical and self-sufficient way to enjoy a soothing soak for years to come.

Portable

Your oasis, anywhere. Unlike permanent spa installations, wood-fired hot tub is designed for complete portability. Its lightweight, flexible design allows for easy assembly and disassembly without special tools. Simply move the compact components to your ideal spot —to seaside,to mountain,to backyard,a shaded garden nook, a lakeside perch, or even take it on your next adventure. Embrace ultimate flexibility and place your perfect soak exactly where you want it, season after season.

Off-Grid Relaxation

True escape awaits. Our wood-fired hot tub delivers the ultimate off-grid experience, freeing you from the demands of modern infrastructure. With no need for electricity, plumbing, or complex hookups, your sanctuary can be placed anywhere—a remote mountain vista, a secluded forest clearing, or a quiet backyard retreat. The simple, elemental process of heating with fire encourages you to disconnect from technology and reconnect with the natural world, offering a profoundly peaceful and self-sufficient haven for pure, uninterrupted relaxation.

Durability

Crafted for generations, not just seasons. The core is coil heater which is built with stainless steel 304. It`s naturally resistant to rot, corrosion, and the extremes of weather, ensuring structural integrity year after year. The simplicity of its design, with no complex electrical components to fail, means this is a low-maintenance investment crafted to provide reliable, unwavering performance and become a lasting centerpiece of relaxation for years to come.

Unique Experience

It provides a rustic and immersive atmosphere that many find appealing.The warm of hot tub and natural smell of wood can provide therapeutic benefits, including relaxation and muscle relief, enhanced by the connection to nature and the ambiance of an outdoor fire.

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4. How to Choose the Right Heater Coil for Your Tub? (Key Factors to Consider When Choosing a Heater Coil)

Choosing the right heater coil for your wood-fired hot tub is a critical decision that affects heating performance, durability, safety, and overall enjoyment. Here is a detailed guide to help you make the best choice.

1. Coil Material: The Most Important Decision

The material dictates longevity, corrosion resistance, and heat transfer efficiency.The coil is subjected to extreme thermal stress (intense fire outside, cool water inside ). The wrong material will fail quickly.

• Your Options:
  • 304 or 316 Stainless Steel: This is the industry standard and highly recommended.
    • 304 SS: Excellent corrosion resistance, durable, and handles thermal cycling well. It’s suitable for most freshwater applications and is the best value for money.
    • 316 SS (“Marine-Grade”): Contains molybdenum, giving it superior resistance to chlorides and corrosion. Essential if you plan to use any saltwater systems (e.g., saltwater chlorination) or if your water source is particularly aggressive. It’s more expensive but offers the best protection.
  • Mild Steel (often coated):
    • Pros: Cheaper upfront cost. Transfers heat very efficiently.
    • Cons: Not recommended. It will rust from the inside out, especially when not in use (“wet rot”). Coatings can burn off or scratch, leading to rapid failure. While stainless steel tube coil is a much wiser long-term investment.
  • Copper:
    • Pros: Excellent heat conductivity (heats water very quickly).
    • Cons: Softer metal, more susceptible to physical damage and corrosion from acidic water (low pH). Can be more expensive. Not as commonly used as stainless steel.Smartclima did a test to compare copper tube coil and stainless tube coil,the test shows: at the begin minutes,copper is faster to heat up, but after 5 minutes,stainless steel can reach the same heating performance and speed as copper pipe does.Smartclima does not suggest to use copper because : 1), Copper tube is easy to corrosion after long time, especially after exposed to high temperatures in long-time burning fire. 2), Copper has a lower melting point than stainless steel, which could be an issue when the wood-fired hot tub coil gets too hot after long-time firing. Also,the angle between two end pipes will become very big when long-time heating. 3), Cost: If you still insist on make coil heater by copper pipe,we strongly suggest the copper pipes OD should be equal to or more than 25mm for high heating performance,and its wall thickness should be more than 1.5mm in order to avoid deform when long-time firing.Obviously,that cost is a big problem..

Suggestion: Choose 304 Stainless Steel for reliability and value. Opt for 316 Stainless if you have any concerns about water chemistry or longevity near saltwater.Not suggest to use copper because of its physical shartage and high cost.

For most people, purchasing a pre-made unit from a reputable manufacturer is the best choice. It ensures safety, efficiency, and saves time.

2. Coil Size (Length and Diameter)

Size directly impacts how quickly and effectively you can heat your tub by heater coil.A larger coil surface area absorbs more heat from the fire and transfers it to the water. The key metric is gallons per minute (GPM) heated per degree, which is a function of surface area.

• Your Options:
  • Small Coils (e.g., 30 ft with 25mm tubing): Suitable for small tubs (under 400 gallons). They will heat faster but may struggle to heat larger volumes in a reasonable time.
  • Medium Coils (e.g., 30ft with 32mm tubing): The most common and versatile size, ideal for tubs between 400 and 600 gallons.
  • Large Coils (e.g., 30+ ft or bigger tubing): Necessary for large tubs,pools (600+ gallons) or for those who want the fastest possible heating times.

Suggestion: Match the coil to your tub size. A small coil is a safe bet for a tub 300-400 gallon. Notice,i.e, when we say 400 gallon tub,usually it will contain 300 gallon water,because a person will soak in it. After you soak in tub,the tub will be full with water.

3. Heat Output and BTU Rating

This measures the coil’s power. A higher BTU rating means faster heating.BTU (British Thermal Unit) measures how much heat the coil can transfer per hour. The rating depends on the coil’s surface area, material, and, crucially, how hot you can build your fire.

• Your Options: Coils can range from 50,000 BTU for small setups to over 200,000 BTU for large commercial ones.
• How to Calculate Your Need:
  • A rough rule of thumb is that you need approximately 100 BTUs per gallon to heat the tub in a reasonable time (a few hours). For a 400-gallon tub, you’d want a coil capable of outputting around 40,000 BTU/hr.
  • Remember, this is highly dependent on your fire-building skills,how to insulate your tub,how to reduce heat loss for your heater coil and external air temperature.

Suggestion: Don’t get fixated on exact BTU numbers from manufacturers, as they are estimates. Focus instead on choosing a correctly sized coil (point #2) made of good material (point #1), improve tub insulation,reduce heat loss for coil and you will get sufficient BTU output.

4. Manufacturer Reputation and Warranty

This is your assurance of quality and safety.A wood-fired hot coil is a significant purchase. A reputable company will use quality materials, proper welding techniques, and stand behind their product.

• What to Look For:
  • Clear Warranty: A multi-year warranty on the coil itself is a sign of confidence in the product.
  • Customer Reviews: Read reviews to see others’ long-term experiences with durability and customer service.
  • Compliance: Check if the manufacturer’s designs meet relevant safety standards.

Suggestion: Invest in a coil from a established company known for quality. It’s cheaper than replacing a failed unit or dealing with a dangerous situation.

By carefully considering each of these details, you will select a heater coil that provides efficient, safe, and reliable heating for your wood-fired hot tub for years to come.

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5. How to Install a Wood-Fired Heater Coil?

How to DIY a Wood-Fired Hot Tub with a Heater Coil? While there are many suppliers offering a wide range of wood-fired hot tub coils on the market, and users may have different types of tubs, the basic setup steps remain largely the same, as outlined below 4 steps:

①, Prepare the Tub & Install Fittings

Start with a clean, sturdy tub, tank or barrel—metal, ceramic, plastic, or any material you can drill into. Drill two holes in the side: one near the bottom for the water inlet, and another about 35 cm higher, making sure it will stay about 5cm below the waterline once filled. Install bulkhead (tub fitting) with watertight fittings into each hole to prevent leaks.

②, Connect the Heater Coil and tub

Attach the wood-fired heater coil to the tub using two hoses (the length depends on the distance between coil and tub, and it can stand high – temperature). For faster heating, choose well-insulated hoses (i.e: silicon hose ) to improve heat retention when water circulate.

③, Secure All Connections

Use stainless steel clamps to tightly fasten the hoses to both the end of heater coil and the tub fittings. Double-check all seals to ensure there are no leaks before filling the tub.

④, Fill water, Fire wood & Relax yourself

You’re all set! Fill water into tub and Add wood blocks to the heater coil, light the fire, and let the water heat for a few hours. Once warm, step in and enjoy your own soothing, wood-fired soaking!

With these straightforward steps, you can successfully assemble your own rustic wood fired hot tub in 30 minutes. It`s an eco-friendly and affordable way to relax outdoors, increasing health without compromising on comfort.

6, Thermosyphon effect may fail or become ineffective under the following conditions:

1, Inadequate Connections: Air can enter the system if connections between the coil and the tub/tank are not airtight—for example, due to loose hoses or improperly fitted connectors.

2, Excessive or Sagging Hose Length: Long runs of hose, particularly those that sag, create too much distance and resistance for the natural circulation to overcome.

3, Significant Height Differences: If the coil is positioned much higher or lower than the water level in the tub/tank, gravity impedes the flow, preventing the thermosyphon cycle from starting or sustaining itself.

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7. How Long Does a Wood-Fired Heater Coil Take to Heat a Tub?

The heating time of a wood-fired heater coil mainly depends on the tub’s water volume, the coil’s specifications, water initial temperature, ambient temperature, as well as the insulation of both the tub and connecting hoses. Generally, smaller tubs heat up faster, while larger ones require more time. Generally, you can get warm and comfortable bathing water within a few hours.

• 1-2 hours for small tubs (500L)
• 2-4 hours for large tubs (1000L+)
• Faster with pump-assisted systems

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8. How to Enhance Heating Efficiency? Tips for Faster Heating Tub Water

1, Use dry, seasoned wood for fire:

Burning dry, seasoned wood ensures a hotter and more efficient fire. Seasoned wood has been allowed to dry for a long time, which means it contains less moisture. This results in a cleaner burn and more heat output compared to green or damp wood, which can produce less heat and more smoke.

2. Insulate the tub:

Proper insulation is crucial for retaining heat. By covering the tub, you reduce heat loss to the surrounding air, and by putting a wood panel under tub bottom, you can reduce heat loss to ground, also, you can coat insulation layer around the tub body, it help to lock heat. The above methods allow the water to stay warmer for longer. This not only saves energy but also helps maintain a consistent temperature, making the heating process more efficient.

3. Use high-temperature standing insulation hose with thicker wall thickness to connect tub and coil.

It is crucial to use a high-temperature standing and well insulated hose with enhanced durability and thermal performance. Connecting with this hose featuring a thicker wall thickness, you can maintain and lock heat during water flowing,reduce heat loss.

4. Use wind deflector around heater coil.

Using a metal panel around your heater coil,it can help fire and heat locked in the coil stove,reduce heat loss,minimize wind impact to fire. So,a wind deflector around a heater coil is a practical solution that enhances heating performance.

5, Keep upper port under water level.

Important! Always keeps the upper outlet port under water level in tub, that means the outlet port must be immerged under water. If not, only the hot water from upper pipe go into the tub, the hot steam will go away into air, which will increase heating time significantly.

6. Use a pump for faster circulation (Optional).

If permit, a pump with small flowing volume helps circulate the water more quickly and evenly. Faster circulation ensures that heat is distributed uniformly throughout the tub, preventing cold spots and speeding up the heating process. This makes the system more efficient and provides a more comfortable experience.

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9. How to protect grass on ground from fire burning when using tub heater coil?

The heat from the coil can easily kill your grass. Follow these easy steps to prevent damage.

1. Create a Solid Base (This is the most important step)

• What to use: A few concrete pavers or a small layer of gravel.
• How to do it: Place the pavers or gravel on the ground where the heater will sit. Make sure the area is larger than the heater itself.
• Why it works: This creates a barrier that absorbs the heat instead of your grass.

2. Use hot ash collecting pan

• Placing a metal ash pan under your heater coil is a great way to protect your grass. It serves two main purposes: it collects falling ash and embers, and it protects grass from burning. Refer to the models with hot ash collecting pan here: https://www.smartclima.com/wood-fired-hot-tub-heater-coil-kit.htm (You can choose Model A2, A4, B4, C1-4, Model X & Y).

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10. Safety Considerations When Using a Wood-Fired Heater Coil

Safety must always come first when using a wood-fired hot tub heater coil. Follow these key guidelines to ensure safe and enjoyable soaking:

1. Keep the Warm Water Return Below Water Level

• The warm water outlet must stay submerged at all times.
• If the water level drops (e.g., when people exit), the coil can overheat, creating scalding or steam hazards.
• Plan your setup carefully, ensuring the outlet remains underwater even after displacement.

2. Always Keep the Coil Full of Water

• The coil must remain completely filled with water—even when people enter or exit the tub.
• Water must circulate freely between the coil and tub without any obstructions.

3. Prevent Dry Firing

• If water stops circulating (due to low water levels), the coil can “dry fire,” leading to dangerous steam or boiling water discharge.
• If you hear knocking, sputtering, or see erratic water flow, extinguish the fire immediately. Let the coil cool, then check your setup.

4. Supervise the Coil at All Times

• Never leave the coil unattended while burning or cooling—especially with children or pets nearby.
• Keep the area clear of flammable materials and ensure the coil is stable to prevent tipping.

5. Fire & Alcohol Don’t Mix

• Exercise caution when combining fire and alcohol near the tub.

6. Monitor Water Temperature

• Unlike electric heaters, wood-fired coils lack built-in thermostats. Use a pool/spa thermometer to check water temperature.
• Without a pump, water temperatures may vary—the area near the outlet will be hottest.

7. Condensation from Burning Wood

• Even dry wood releases moisture when burned. If you see water dripping from the coil, it’s likely condensation (not a leak).

8. Perform a Safety Check Before First Use

• Inspect your setup and surroundings for potential hazards before lighting the fire.

By following these precautions, you can enjoy a safe, relaxing wood-fired hot tub experience. Always prioritize safety! 

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11. How to Maintain a Wood-Fired Hot Tub? Tips for Longevity

Over time, your wood-fired hot tub’s heating coil can accumulate soot and dirt. While cleaning isn’t necessary, a little maintenance can restore its stainless steel shine. Here’s a simple method to get it looking like new:

Step 1: Rinse Off Loose Debris

Start by hosing down the coil to remove excess dirt and soot.

Step 2: Apply Oven Cleaner

Use a heavy-duty oven cleaning spray (following the product’s instructions). Since these sprays contain strong chemicals, work in a well-ventilated area and wear proper PPE (gloves, goggles, etc.).

Step 3: Let It Sit, Then Rinse

Allow the cleaner to work (ours takes about 30 minutes), then thoroughly rinse off the residue with a hose.

Step 4: Done!

That’s all it takes—your heating coil is now clean and ready for your next relaxing soak. Enjoy!

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Choose Smartclima as your best supplier of wood fired hot tub coil

Investing in a quality wood‑fired hot tub coil is more than just an upgrade to your outdoor space—it’s a commitment to sustainable, off‑grid relaxation that connects you to nature while delivering reliable warmth year after year. With Smartclima’s durable, efficient designs and straightforward care, you can enjoy safe, cost‑effective, and timeless comfort in your own backyard for years to come.