Wood Fired Pool Heater Coil –A Big Heating Coil for Large Hot Tubs & Swimming Pools

This large wood fired heating coil is built for people who have outgrown a standard barrel-tub coil. With 32mm seamless stainless steel tubing, a 40cm coil diameter and 10 spiral circles, it puts dramatically more tubing in contact with the fire than a standard 25mm coil with 8 circles — so large hot tubs and small pools reach soaking temperature faster, on less firewood.

Like every Smartclima thermosiphon coil, it needs no pump and no electricity. The fire heats the water inside the coil, hot water rises into your tub, and cooler water is drawn back down to the fire to replace it. The loop runs on heat and gravity alone — nothing to plug in, nothing to fail.

Why a bigger coil heats faster

Three things change when you scale a coil up, and they compound:

1. A wider bore (32mm vs 25mm). Larger tubing carries more water per pass and exposes more surface area to the flame, while reducing flow resistance so the thermosiphon circulates more freely.
2. A wider coil (40cm). A larger diameter means every spiral circle is longer, so you fit more tubing into the same height of firebox.
3. More circles (10). Each extra circle adds heat-exchange length and gives the water more time inside the fire before it returns to the tub.

More surface area in the flame and a longer path through it means a bigger temperature difference between the water entering and leaving the coil — and that difference is what drives both faster heating and stronger circulation.

Specifications for large heating coil

Standard heating coil VS. Large heating coil

Unique features （Why the quality of Smartclima coil is better than other suppliers`?)

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.

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.

Smartclima coil is equipped with heavy-duty industrial silicone heat-resistant hoses matched with high-temperature resistant 304 stainless steel tub 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.

What size tub or pool will it heat?

This is the honest answer, because a coil that is oversold is a coil that disappoints:

• Large barrel tubs and big stock tanks — excellent match. This is the sweet spot. You get noticeably faster heat-up than a 25mm coil, and the tub holds temperature well once it is there.
• Plunge pools and small above-ground pools — good match, with a cover. A cover is not optional here; without one you are heating the sky.
• Full-size swimming pools — possible, but be realistic. Water volume and surface heat loss scale faster than any coil does. Heating a full-size pool with wood means a large, sustained fire and a lot of firewood. If that is your plan, use this coil as a season-extender and keep the pool covered when heating but not in use, rather than expecting gas-heater speed.
• It can also serve as an auxiliary heating device for pool heat pumps to reduce the working load of the heat pump and cut its operating costs.

Installing a large coil

1. Mount the coil below the water level of your tub or pool. Gravity-fed thermosiphon circulation needs the cold inlet lower than the hot outlet.
2. Support it properly. A 40cm coil full of water is heavy. Set it on a stable, heat-safe base rather than bare grass or a wooden deck.
3. Keep the return line rising the whole way back to the tub, with no dips or sagging hose. Any low spot traps air and stops circulation.
4. Fill and bleed before lighting. The loop must be completely full of water with no trapped air. Check for bubbles at the return outlet first.
5. Keep the return outlet submerged below the water surface. This ensures all heat from the outflow transfers into the water instead of escaping into the air.
6. Feed it dry hardwood and give it airflow. A big coil rewards a proper fire. Wet or soft wood wastes most of the heat you paid for in labour.

For a full step-by-step build, see our guide to building a wood fired hot tub with a heater coil.

Available configurations （Optional parts)

The coil is available as the coil alone, or with any combination of the accessories that make outdoor use easier:

• Integrated fire shield / smoke deflector (detachable) — traps heat around the coil for better efficiency
• Rain deflector supports — for reliable all-weather operation
• Hot-ash collection pan — protects ground and grass
• Heat-resistant hose — keep water temperature when transit water to tub
• Stainless Steel Tub Fitting — No melt when hot water flows into tub
• BBQ grill — cook while the water heats

If you need a different bore, diameter or number of circles for a specific project, we also build custom stainless steel tubing coils to order. Just contact us by Email: wood-fired-tub@smartclima.com

Frequently asked questions