If you've been looking for a wood fired hot tub coil kit for sale, you're probably already dreaming about those crisp autumn evenings spent soaking in steaming water while the smell of woodsmoke drifts through the air. There is something fundamentally satisfying about heating your own water with nothing but a few logs and a bit of patience. It's a far cry from the plastic, buzzing, high-maintenance electric tubs you see at the big-box stores. Plus, building one yourself using a kit is a heck of a lot cheaper than buying a pre-made cedar soak tub that costs as much as a used car.
The beauty of a wood-fired system lies in its simplicity. You aren't dealing with circuit boards, expensive heating elements, or a massive spike in your monthly power bill. Instead, you're relying on a bit of basic physics—specifically, something called a thermosiphon. But before you start digging a hole or buying a stock tank, you need to understand what you're actually getting when you look for a kit and how to make sure you're not just buying a heap of scrap metal.
What exactly is in a coil kit?
When you find a wood fired hot tub coil kit for sale, you aren't just buying a spring-shaped piece of pipe. Well, you shouldn't be, anyway. A decent kit usually includes the heat exchange coil itself, the bulkhead fittings to get the water through the wall of your tub, and some high-heat resistant hoses to connect the two.
The coil is the heart of the whole operation. It's designed to sit inside a fire pit or a specialized stove box. You build a fire right in the middle of the coils. As the fire burns, it heats the water sitting inside the pipe. Because hot water is less dense than cold water, it naturally rises, flowing out of the top of the coil and into your tub. This creates a vacuum effect that pulls cold water from the bottom of the tub into the bottom of the coil. It's a self-circulating loop that requires zero pumps and zero electricity. It's pretty brilliant when you think about it.
Choosing between copper and stainless steel
This is the big debate in the DIY hot tub world. Most kits you'll see for sale will be made from either copper or stainless steel. Both have their fans, and both have their drawbacks.
Copper is the king of heat transfer. It conducts heat much faster than stainless steel, which means your water is going to get up to temperature a lot quicker. If you're the type of person who decides at 4:00 PM that they want a soak by 6:00 PM, copper might be your best bet. However, copper is softer and can be more prone to damage if you aren't careful. It also doesn't play well with certain chemicals. If you're planning on using chlorine or bromine, stay away from copper; it'll corrode and turn your water (and potentially your hair) a funky shade of green.
Stainless steel is the "set it and forget it" option. It's incredibly durable and can handle pretty much any water treatment you throw at it. It's also much more resistant to the high heat of a roaring wood fire over long periods. The downside? It doesn't conduct heat quite as efficiently as copper. You might be waiting an extra hour for that tub to reach the "perfect" temperature, but you can rest easy knowing the coil will probably outlive the tub itself.
Why a kit is better than a DIY "hack"
I've seen plenty of people try to make their own coils by wrapping copper fridge tubing around a bucket. It can work, but it's often a recipe for frustration. When you buy a professionally made wood fired hot tub coil kit for sale, the pipe diameter is calculated for optimal flow. If the pipe is too narrow, the water won't circulate fast enough and might actually boil inside the coil, which sounds like a tea kettle and can be a bit sketchy.
Professional kits also use thick-walled tubing. Remember, this thing is sitting directly in a fire. Cheap, thin-walled hobbyist tubing can warp or even melt through if the fire gets too hot and there's no water moving through it. A dedicated kit gives you the peace of mind that the fittings won't leak the second things get pressurized.
Setting up your backyard spa
Once you've got your kit, the fun really starts. Most people pair these kits with a galvanized stock tank—those big metal troughs you see on farms. They're rugged, relatively cheap, and they look great in a rustic backyard setting.
The setup is pretty straightforward. You'll need to drill two holes in the side of your tub. One goes near the bottom (this is your intake) and one goes near the top (this is your return). You connect the coil to these holes using the hoses and fittings provided in the kit.
The most important thing to remember is the height of the coil relative to the tub. For the thermosiphon to work properly, the coil needs to be positioned correctly. If the coil is too high or too low, the water won't circulate naturally, and you'll end up with a fire that's hot as blazes and a tub that's still ice cold. Usually, you want the bottom of the coil to be roughly level with the bottom of the tub.
Safety and maintenance tips
It sounds obvious, but you're dealing with fire and hot water, so you've got to be smart. Always make sure the coil is full of water before you light the fire. If you fire up the pit with a dry coil, you'll ruin the metal in minutes.
Also, consider the "ouch" factor. The water coming out of the top return pipe can be incredibly hot—hot enough to scald you. Most people install a diverter or just make sure they aren't sitting right in front of the jet when the fire is roaring.
As for maintenance, it's mostly about keeping the coil clean. Over time, soot can build up on the outside of the coils, which acts as an insulator and makes the heater less efficient. A quick scrub with a wire brush every few uses will keep it performing like new. If you live in a climate where the ground freezes, you absolutely have to drain the coil when you're not using it. Water expands when it freezes, and it will split even the strongest stainless steel pipe like a twig.
Finding the right kit for sale
So, where do you actually find a wood fired hot tub coil kit for sale? You won't usually find them at your local hardware store. Your best bet is looking at specialized off-grid living shops or online marketplaces. Etsy has some fantastic independent metalworkers who specialize in these, and they often use higher-quality materials than the mass-produced stuff you might find on giant retail sites.
When you're browsing, look at the reviews specifically for "flow rate" and "sturdiness." You want a seller who knows their physics. Don't be afraid to ask questions about the grade of stainless steel or the wall thickness of the copper.
Wrapping it up
Building a wood-fired hot tub is one of those projects that feels deeply rewarding. There's a certain magic to sitting in a tub you built yourself, watching the sparks fly up into the night sky, knowing you aren't burning a dime of electricity. It takes a little more effort than flipping a switch on a plastic spa, but that's exactly the point.
By picking up a high-quality wood fired hot tub coil kit for sale, you're skipping the hardest part of the engineering and getting straight to the good stuff. Just add water, some dry firewood, and maybe a cold drink, and you've got the best seat in the house—or rather, the best seat in the yard. It's an investment in your relaxation that'll last for years, and honestly, your backyard deserves it.