What is Fireflow?
Fireflow is a precision-engineered stainless steel coil system that transforms any water-tight container into a beautifully simple wood-fired hot tub.
Light a fire within the coil and as the water heats, it naturally circulates back into your tub through a process called thermosyphon - no electricity, no pumps, no complex mechanics.
Just wood. Water. Fire. Flow.
Using ThermaTubs
Do I need electricity or a pump?
No, ThermaTubs are designed to work completely without electricity or pumps it is fully off-grid.
The system uses a natural process called thermosyphon circulation. As water inside the stainless steel coil heats, it becomes lighter and rises back into the tub while cooler water flows down into the coil to replace it. This creates a continuous natural circulation powered only by fire and gravity.
As long as there is fire, the water will continue to circulate and heat.
A pump is not required, but one can be added if desired. Using a small circulation pump can increase the speed that water moves through the coil, which may help heat larger volumes of water more quickly particularly in larger tubs or above-ground pools.
However, for most standard tubs the natural thermosyphon flow provides excellent circulation without any mechanical assistance.
No wires.
No pumps.
Just fire, water and natural flow.
How long does it take to heat?
Heating time depends on a few factors, including the size of the tub, the starting water temperature, the strength of the fire and the outside weather conditions.
As a general guide:
- 2-person tubs: around 1–2 hours
- 6-person tubs: around 2–4 hours
Maintaining a strong, steady fire will heat the water more quickly, while colder weather or larger water volumes will naturally take longer.
Some customers choose to add a small circulation pump to increase the flow of water through the coil, which can help speed up heating in larger tubs or above-ground pools.
Once the water reaches your desired temperature, simply stop adding wood and allow the fire to burn down.
How hot does it get?
With a well-maintained fire, the water can comfortably reach 37-40°C, which is the typical temperature range for a relaxing hot tub.
If the fire is kept strong, temperatures can rise higher than this, so we recommend monitoring the water temperature and adjusting the fire as needed.
Because the system heats gradually, you have plenty of time to control the temperature, simply add more wood to increase heat or allow the fire to burn down to stabilise it.
Most people find the ideal soaking temperature is around 38°C.
What fuel should I use?
Fireflow works just like a small campfire, so almost any dry wood can be used.
Seasoned firewood such as oak, ash, or birch works especially well because it burns hotter and longer, but the coil will also work perfectly with smaller logs, kindling, or pieces of scrap wood you may have on hand.
The key is simply maintaining a small steady fire within the coil.
We recommend avoiding treated, painted, or chemically treated wood, as these materials can release harmful fumes when burned.
Installation
Is installation complicated?
No, installation is simple and requires only basic tools.
The ThermaTubs Coil Kit is designed for straightforward DIY setup. In most cases, installation involves drilling two holes in your tub for the inlet and outlet fittings, connecting the supplied hoses, and ensuring the coil is positioned securely above the fire.
Once everything is connected, simply fill the tub with water before lighting the fire and the system will begin circulating naturally through thermosyphon.
Most customers are able to complete installation in 30–60 minutes.
Full instructions are provided with every kit, and if you ever need help our team is always happy to assist.
What size tub can I use?
Fireflow can be used with almost any water-tight container.
Many people use stock tanks, plunge tubs, ice baths, or traditional wooden tubs, but the coil will work with anything that safely holds water.
Smaller tubs will heat more quickly, while larger tubs simply take longer to warm up.
As a general guide, Fireflow works very well with tubs in the 200-800 litre range, which covers most single and two-person setups.
Larger tubs or small above-ground pools can also be heated, they may just require a larger fire or longer heating time.
Can the coil overheat?
When the system is set up correctly and water is circulating, the coil will not overheat.
The flowing water inside the coil naturally absorbs the heat from the fire and keeps the metal at a safe operating temperature.
For this reason, it’s important to always ensure the tub is filled with water and the hoses are connected before lighting a fire. Once water is circulating through the system, the coil is continuously cooled as it heats the tub.
The coil is made from durable stainless steel and is designed to handle the temperatures produced by a wood fire when used as intended.
Orders & Delivery
When will I get my order?
Orders are processed within 1–3 working days, and tracking details are provided once your order has been dispatched.
Delivery typically takes around 10–21 days, although many orders arrive sooner depending on shipping conditions and destination.
We provide free shipping on all orders, and you’ll be able to track your delivery every step of the way.
Transit times can occasionally vary slightly during busy periods, but we will always keep you informed while your order makes its way to you.
What is the return policy?
Our goal is for every customer to be totally satisfied with their purchase. If this isn't the case, let us know and we'll do our best to work with you to make it right.
We accept returns within 14 days of delivery, provided the product is unused, uninstalled and in its original condition.
As our systems are used with fire and water, we cannot accept returns on items that have been used or exposed to heat.
If your order arrives damaged or faulty, please contact us within 48 hours with photographs and we will resolve the issue promptly.
Do I have to pay shipping fee?
Shipping is free on all orders.
In most cases, there are no additional customs or import fees to pay when your order arrives.
Very occasionally, customs authorities may apply duties or handling charges depending on local regulations. If this happens, the customer would be responsible for those fees.
Once your order has been dispatched, you’ll receive tracking details so you can follow its progress all the way to delivery.
Safety
Is it safe to use?
Yes, when used responsibly and according to the instructions, ThermaTubs systems are safe and reliable.
The system works using natural thermosyphon circulation and contains no electrical components, pumps or pressurised parts. As long as water is able to circulate freely and the tub is filled before lighting a fire, the system will operate safely.
Because the product involves open fire, hot water and bathing, basic safety precautions should always be followed:
- Always ensure the tub is filled with water before lighting a fire
- Never light the coil when the system is empty
- Monitor the water temperature before entering
- Never leave an active fire unattended
- Keep children supervised at all times around the tub and fire
- Ensure hoses and fittings are correctly installed before use
Used correctly, ThermaTubs provides a simple and safe way to enjoy wood-fired outdoor bathing.
Any more questions?
If you need help or can’t find the information you’re looking for, feel free to reach out and we’ll be happy to assist.
Safety Notice & Disclaimer
ThermaTubs systems involve the use of open fire and hot water. By purchasing and using this product, customers acknowledge that these elements carry inherent risks if not used responsibly.
Users are responsible for ensuring the system is installed and operated safely and in accordance with the instructions provided. The tub must always be filled with water before lighting a fire, and the system must remain open to allow proper water circulation.
Children should always be supervised around the tub and fire, and the fire should never be left unattended.
ThermaTubs accepts no liability for injury, damage, or loss resulting from misuse, improper installation, modification of the product, or failure to follow the provided safety guidance