Wood fired hot tub heater coil kit – All models

A wood fired hot tub heater coil kit turns almost any water container into a wood-burning spa without electricity or gas. Smartclima’s coil kits are built from food-grade stainless steel and ship in 24 standard models (A1 through F4), each designed to heat barrels, stock tanks, inflatable tubs, and small pools using nothing but firewood and natural water circulation. Free shipping is included to the United States, Canada, Australia, New Zealand, the EU, the UK, Ireland, and Japan.

TL;DR: The Smartclima wood fired hot tub heater coil kit is a food-grade stainless steel heat exchanger that converts barrels, stock tanks, and inflatable tubs into off-grid hot tubs. 24 standard models cover most container sizes, custom fabrication is available for non-standard builds, and free shipping reaches North America, Europe, Australasia, and Japan.

How a Wood Fired Hot Tub Heater Coil Works

The coil is a fire-powered heat exchanger. You build a wood fire inside or beneath the coil’s spiral, and water inside the tubing heats up. Hot water is lighter than cold water, so it rises out of the top of the coil and flows into your tub, while cooler water from the bottom of the tub is drawn into the coil to replace it. This continuous loop is called thermosiphon circulation. It needs no pump, no electricity, and no moving parts. As long as the fire burns, water keeps circulating and the tub gets warmer.

A typical 200-litre stock tank reaches 38 to 40 °C (100 to 104 °F) in 60 to 90 minutes depending on fire intensity, ambient temperature, and wind. Once you reach your target temperature, you let the fire burn down or add a rain deflector to protect the fire box while the coil keeps the water warm.

Product Information

Why Food-Grade Stainless Steel

The coil sits in hot water that touches your skin, so the material matters. Smartclima uses food-grade stainless steel that meets international drinking-water safety standards. This means no harmful metal leaching occurs during heating, even at high temperatures over many years of use. Food-grade stainless steel also resists corrosion from minerals, chlorine, salt, and acidic water far better than ordinary steel or galvanised alternatives.

For outdoor installations exposed to rain, snow, and freeze-thaw cycles, stainless steel is the practical choice. A coil left outside year-round in wet weather will not rust through the way carbon steel will, and it will not develop the pitting and scaling that shorten the life of cheaper alloys. With proper winter draining, the coil delivers a 20+ year outdoor service life.

Three Engineering Advantages

Seamless Extruded Stainless Tube

Smartclima coils are made from extruded seamless tubing with uniform wall thickness. Seamless tube has no welded seam along its length, which means there is no weak point where pressure, freezing, or corrosion can start a leak. The even wall thickness distributes thermal and mechanical stress evenly, giving the coil higher pressure resistance and better freeze resistance than seamed tubing. The result is zero leak risk and zero rust risk over decades of outdoor use.

One-Piece Bent Full Coil (No Welded Joints)

Each coil is bent from a single continuous length of tubing. There are no connecting welds between spiral turns, which eliminates the joints that are the most common failure point on ordinary heater coils. Welded joints corrode first, crack under thermal cycling, and leak. By removing them entirely, Smartclima coils sustain reliable anti-corrosion performance for the full life of the product.

Premium High-Temperature Hose and Stainless Fittings

The hose that connects the coil to your tub is thick industrial silicone rated for sustained high temperatures. It will not melt, crack, or harden under extreme hot and cold weather, unlike plastic or regular rubber hoses that fail after one or two seasons. The tub connector fittings are stainless steel with tool-free quick clamps, so installation takes minutes and the fittings match the coil’s long service life rather than becoming the first part to replace.

Full Model Range: 24 Standard Sizes

The A through F series gives you 24 distinct coil models to match your container size, fire box dimensions, and heating-speed requirements. Each series (A, B, C, D, E, F) includes four variants (1, 2, 3, 4) that differ in coil dimensions and heating capacity. Whether you are heating a small 100-litre barrel or a large 500-litre stock tank, there is a model sized for the job.

All models share the same 25 mm tubing diameter, universal hose connectors, and food-grade stainless steel construction. The differences are in coil outer diameter, height, and the number of heating surfaces exposed to fire, which determines how fast the water heats.

If none of the 24 standard models fits your container or fire box, Smartclima offers full custom stainless steel tubing coil fabrication. Send your dimensions and requirements and we will build a coil to your specification.

What Is Included in the Kit

Each wood fired hot tub heater coil kit ships with:

• One food-grade stainless steel heater coil (your selected A1–F4 model)
• High-temperature industrial silicone hose
• Stainless steel tub connector fittings with tool-free quick clamps
• Sealing cap for the tub fitting

Optional add-ons available on this product page include a height-adjustable BBQ grille kit, a rotatable dual BBQ grill kit, a fire oven, a rain deflector, a second spare heater, and a carrying bag. You can also add a portable tub kit for one person or a portable tub kit for multiple people if you do not already have a container. For a complete turnkey setup, see our Dutch-style wood fired hot tub.

Installation Guide

1. Choose your container. The kit fits wooden barrels, plastic stock tanks, small above-ground pools, inflatable hot tubs, and custom metal vessels. The container wall needs a hole large enough for the hose connector.
2. Mount the coil. Position the coil so the fire box sits beneath or beside the coil spiral. The coil can be freestanding or mounted to a stand.
3. Connect the hose. Attach the silicone hose from the coil’s top outlet to the upper fitting on your tub, and from the coil’s lower inlet to the lower fitting on your tub. Use the quick clamps to secure each connection. No tools are required.
4. Fill the tub. Fill your container with water before lighting the fire. The coil and hoses must be full of water before heating begins.
5. Light the fire. Build a wood fire in the fire box beneath the coil. Within minutes, water inside the coil begins to heat and circulate.
6. Monitor the temperature. Check the water temperature periodically. A 200-litre tub typically reaches soaking temperature in 60 to 90 minutes.
7. Maintain or extinguish. Add wood to maintain heat, or let the fire burn down to stop heating. The coil continues circulating warm water until the fire is out.
8. Drain for winter. In cold months, drain the coil and hoses fully after each use to prevent freeze damage.

Application Scenarios

• Off-grid cabin and wilderness retreat soaking. No grid power is needed. Firewood heats the tub water, making the kit ideal for remote properties.
• Backyard DIY hot tub projects. Repurpose an old stock tank or wooden wine barrel instead of buying an expensive pre-built spa.
• Camping and glamping site amenities. The kit is portable and installs in minutes, making it practical for tourist sites that offer outdoor soaking.
• Homestead and self-sufficient living. Zero fossil fuel, zero electricity, and zero running cost beyond firewood.
• Custom outdoor landscape spa builds. Pair the coil with an inflatable portable tub or a custom-built vessel for seasonal backyard relaxation.

Custom Manufacturing and OEM

Smartclima operates its own manufacturing facility in Ningbo, China, with full capability in stainless steel tube bending, sheet metal fabrication, and custom coil design. Beyond the 24 standard models, we build custom coils to buyer specifications for non-standard containers, commercial spa installations, and OEM branding projects.

Custom options include:

• Non-standard coil diameters, heights, and tubing gauges
• Custom spiral turn counts for faster or slower heating
• Branded packaging and private-label labelling for resellers
• Bulk production runs for distributors and spa manufacturers
• Matching custom fire boxes, stands, and accessory kits

To request a custom quote, send your container dimensions, desired heating time, and target order quantity. We will provide a coil specification, pricing, and production timeline. See also our custom stainless steel tubing coil page for more on our fabrication capabilities.

Shipping and Regional Availability

Free standard shipping is included for orders delivered to the United States, Canada, Australia, New Zealand, EU member states, the United Kingdom, Ireland, and Japan. Orders to these regions typically ship within 1 to 2 business days and arrive in 3 to 5 business days.

Customers in other regions, including Scandinavia, the Middle East, Southeast Asia, and South America, should send a pre-order inquiry to confirm shipping rates and delivery timelines before placing an order.

The kit ships in a single package weighing 9 kg with dimensions of 50 × 40 × 30 cm, which keeps international shipping costs manageable even outside the free-shipping regions.

About Smartclima

Smartclima Co., Ltd. is a manufacturer and global supplier based in Ningbo, Zhejiang, China. Founded in 2001, the company has over 20 years of export experience and has served more than 10,000 customers worldwide. Our wood fired hot tub coil designs are patent-protected, and every coil is produced in our own facility under direct quality control rather than sourced from a third-party factory.

Our manufacturing capability spans stainless steel tube bending, sheet metal fabrication, cold forging, die-casting, plastic injection moulding, and rubber moulding. This means we control the full production process from raw tubing to finished kit, which is how we maintain consistent material quality, dimensional accuracy, and long-term durability across all 24 models.

We stand behind every coil with a 30-day return policy for orders shipped to the US, Canada, the UK, and Australia, with free return shipping by mail. If a coil arrives damaged or does not meet specification, contact us and we will replace it. Browse the full range in our wood fired tub coils category.

Frequently Asked Questions