Wood-Fired Hot Tub Review: An Honest Weekend With an Off-Grid Tub

Last updated: September 2026

A while back I went away with the family for the weekend. It was another anniversary of my mum’s 21st birthday (strange how I’m in my forties and she never gets any older). The house we stayed in had a wood-fired, off-grid hot tub in the garden. My experience of wood-fired tubs had been pretty limited. I’ve designed a couple of builds that used a “coil” in a fire to heat the water, but the principle is a bit different. So this was going to be interesting.

This is my honest review of that weekend: what worked, what really didn’t, and what you’d need to change to make a wood-fired tub something you’d actually want to own.

What is an off-grid, wood-fired hot tub?

This one was totally off grid. No electricity, no pumps, no jets, no filter. There wasn’t even an electric thermometer, just a floating one. It’s a tub of water with a wood-burning stove built in.

The heating works by convection. Water in the stove’s jacket gets hot, rises and flows out into the tub, and cooler water is drawn in to take its place. There are a few common designs:

Design	How it works	Things to know
Internal stove	The firebox sits in the water, with a guard to keep bathers off it	Heats directly, but takes up seating space
Integrated side stove (like this one)	The stove is built into the tub wall, and you load it from the outside	Neater, and no ash in the water. The outlet vents get very hot
External stove or coil	A separate stove or a coil in a fire, connected to the tub with pipes	Frees up the inside of the tub. Can be combined with a pump and filter

If you want the bigger picture on going without mains power, read Off-grid hot tub: luxury in the wild or impossible dream?

First impressions

At first glance it looked pretty neat. A tall chimney took the smoke well above your head, with a heat guard around it so you wouldn’t burn yourself or damage the cover. It had a proper insulated hot tub cover, a moulded plastic shell inside and timber cladding outside. The build quality was good, and the stove was particularly well made. I was impressed. I had no idea what it cost, but it certainly looked the part.

Building the fire

Apart from being on your hands and knees lighting a fire, then feeding it and keeping it going long enough to heat the water, it wasn’t that bad. Yes, it’s a hassle. It’s not like pressing a couple of buttons on an app and coming back an hour later. It’s involved. Some people will love that. It’s a bit like a barbecue: half the fun is the fire.

Use dry, seasoned wood. Wet wood smokes, heats badly and annoys the neighbours. In the UK, if you live in a smoke control area, wood can only be burned in exempt appliances, and there are fines for releasing smoke (GOV.UK smoke control rules). Check with your council before you buy one for a town garden.

Heat-up time

The very kind owner had clearly lit a fire before we arrived, because the tub was holding at around 34°C (93°F). I built quite a big fire with some big logs, and was pleasantly surprised that it reached about 39°C (102°F) in around 50 minutes. That’s much quicker than a spa pack’s electric heater, and comparable with propane, natural gas or my big air source heat pump on a warm day.

But that was from a warm start. The next day, from cold (more on why below), we gave up after about three hours. We’d started late in the afternoon and simply ran out of daylight. Given more patience, we would have got there eventually. For reference, one current maker, Skargards, quotes 1.5 to 3 hours from 6°C to 39°C for its current Regal models, depending on the size and the stove, and says heating times vary with the weather, the wood and the starting temperature. A good lid makes a real difference.

Checking the temperature

With no electricity, we were relying on a floating thermometer. It works, but every time you lift the cover to check it, you lose heat, and if it drifts into the middle you have to fish it out. I much prefer glancing at my app or the topside control on the wall. If I owned one of these, the first thing I’d buy is a wireless floating thermometer with a display you can see from the house, like the Inkbird IBS-P02R.

Hot spots and hot vents

I’m a bit funny about getting into other people’s hot tubs these days, especially rental ones, so I left the actual “testing” to the rest of the family.

The first thing they noticed was that the heat was concentrated around the stove. With no pump, nothing mixes the water except convection, so there were hot and cold parts of the tub. The vents where the hot water came out got incredibly hot too, like “going to burn you if you touch them” hot. That could definitely leave its mark on your leg.

If you’re in one, give the water a stir with a paddle now and then, and keep children well away from the vents and the stove.

No thermostat means it overheats

This was the part I hadn’t really thought about. On a normal hot tub, or any of our DIY builds, a thermostat controls the heater. You get up to temperature and it holds it there. With this wood-fired tub, there was no regulation at all. As the fire kept burning, the water kept getting hotter. By the time some of the “testers” called it a day, it was at 44°C (111°F). Far too hot for me.

That matters. The CDC says hot tub water should not be higher than 104°F (40°C). If you misjudge the size of the fire, the tub will keep heating. You’d get out before you scalded yourself, but it’s easy to overheat your body without realising, especially after a drink.

How to manage it:

• Build a smaller fire as you get close to temperature, and use the stove’s air control to slow it down.
• Stop adding wood at around 37–38°C. The stove keeps giving heat for a while after.
• Keep a thermometer in the water the whole time and check it.
• If it’s too hot, cool it down by closing the air vents, taking the lid off, or adding cold water from a hose.
• Keep soaks short at higher temperatures. My post Are hot tubs good for your health? covers safe times and temperatures.

The next day: why filtration matters

The next morning I opened the cover to see if it had held its heat. It had, somewhat. But I was greeted by what I can only describe as a stale, dirty-water stench. It was horrible, verging on disgusting, and I don’t have the best sense of smell. Everyone had showered before getting in, too.

With no filter and no sanitiser, there’s nothing to deal with what people bring into the water: sweat, skin, cosmetics and germs. Warm water is the perfect place for bacteria to grow. The CDC links poorly maintained hot tubs with skin, respiratory and stomach illnesses, including “hot tub rash” from Pseudomonas bacteria. It recommends at least 3ppm chlorine or 4–8ppm bromine, and a pH of 7.0–7.8.

Nobody was getting in that tub as it was, so it was time to empty it, and quick.

Draining and refilling

After we eventually found the drain lever (it wasn’t obvious, and we didn’t have the manual), draining took well over an hour. At the time I guessed it held about 800 litres (200 US gallons). Similar tubs on sale today typically hold 1,200–1,800 litres, so it may well have been more. Then we had to clean it down before refilling, and filling from a hosepipe took at least another hour.

Where does the water go? We tipped it on the flower beds, which is fine for untreated water. If you’ve added chlorine or bromine, let it drop to zero first, and don’t drain it into a stream or surface water drain.

Add it all up. An hour to drain, an hour to fill, time to build a fire, then three hours or more to heat from cold. That’s a lot of time just to get in a tub. It may be cheaper to run than electric, but your time has a cost too. I’ll let you decide what it’s worth to you. For me, doing this every time I want a soak is a no-go.

My verdict: is it a hot tub or an outdoor bath?

I’m going to be totally honest. As it was set up that weekend, with no filter and no sanitiser, I don’t think this is a hot tub. It’s an outdoor bath. Maybe I’m biased by what I design for customers, but if the water is single-use, in my eyes it’s a bath. My mum’s verdict on the lack of jets? “Boring.”

That said, the wood-fired part works, and I can see the appeal: a crackling fire, no electricity bill and no power supply needed. It was faster than electric from a warm start, and depending on what you pay for logs, it can be cheap to run.

What I liked	What I didn’t
Looked great and felt well built	No thermostat, so it overheated to 44°C
Fast heat-up from warm	Slow from cold (we gave up after 3 hours)
No electricity needed	No filter or sanitiser, so the water went off overnight
The fire is part of the fun	Hot spots and very hot vents
Cheap to heat if you have logs	Hours of draining, filling and heating each time

How I’d make a wood-fired tub work

Most of the problems come from having no filtration and no sanitiser, not from the wood fire. Fix those and it becomes a very different tub.

• Add filtration. Some makers now sell a filtration system as an accessory (£510 at the time of writing), which one maker says lets you keep the same water for multiple weeks. Electric frost protectors are also available. A pump also mixes the water, so it gets rid of the hot spots.
• Use a sanitiser. Chlorine or bromine, tested and topped up, as in my hot tub chemical levels guide. UV and active oxygen help, but they don’t leave a lasting sanitiser in the water on their own. A salt system makes chlorine, so that works. There’s more in Are there any alternatives to chlorine for my hot tub?
• Get a good insulated lid. It holds the heat overnight, so you’re not starting from cold.
• Use a wireless thermometer so you can watch the temperature without lifting the lid.
• Accept it’s a weekend tub. Even with all of that, you’ll still be lighting a fire every time you want to use it.

Filtration and a pump need some power, of course. So it’s no longer fully off grid, but a small circulation pump uses far less than a heater.

Building your own instead?

If you like the look of a timber tub but want filtration, heating control and jets, you can build one. My guide on how to build a DIY wooden hot tub walks through it. My complete cedar/wood hot tub plumbing kit (heating and filtration only) gives you a circulation pump, a 25 sq ft cartridge filter and a Balboa spa pack with a thermostatically controlled heater and topside control. There are also 4-jet, 8-jet and 16-jet versions if you’d rather not have my mum calling it boring.

A stock tank is another budget-friendly route. See How to build the ultimate DIY stock tank hot tub and 3 budget-friendly DIY hot tub ideas. And if cheap heating is the attraction, read How to heat a hot tub for free.

For a full in-ground build, my DIY hot tub plans give you CAD drawings, the plumbing layout, a parts list and the video course.

FAQs

How long does a wood-fired hot tub take to heat up?

From cold, typically a few hours. One current maker quotes 1.5–3 hours from 6°C to 39°C. From a warm start, ours gained 5°C in about 50 minutes.

How do you stop a wood-fired hot tub overheating?

Watch a thermometer, stop adding wood at around 37–38°C and close down the air supply. If it gets too hot, take the lid off or add cold water. Don’t go above 40°C (104°F).

How often do you need to change the water?

With no filtration or sanitiser, after every use. Ours had gone off by the next morning. With filtration and a proper sanitiser, it can last weeks.

Can you put chlorine in a wood-fired hot tub?

Check your tub’s manual first, as makers set their own limits for the shell, timber and stove. If it’s allowed, keep levels within the CDC range and test regularly.

Can I use a wood-fired hot tub in a smoke control area?

In a UK smoke control area, wood can only be burned in exempt appliances. Check with your local council before you buy.

Have you got a wood-fired tub? I’d love to hear how you get on with it in the comments below. I read them all.

Cheers,
Andi

You can also find me on my socials;

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

Thanks - Andi

 

Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi