Off Grid, Wood Fired Hot Tub Review

In this video, I will review an off grid, wood fired hot tub.

The tub was a wood fire off grid hot tub. I must admit, my experience with wood fired hot tubs has been pretty limited. I have done a couple of designs and builds that have used “coil” fire heat but the principle is a little different.

This particular hot tub was something that you would classify as being totally “off grid”. No electric. No pumps, no jets, just a tub and a wood fire heater. There wasn’t even an electric thermometer! It was a floating ‘thing’ This was going to be interesting….

Wood Fire, Off Grid Tub – The Appearance

On first glance, it looked pretty neat. There was a large chimney protruding from the tub to take any smoke well above you. There was a nice heat guard around this so you would not burn yourself or damage the cover.

The cover was a regular cover for a hot tub and the tub itself was encased with a wood finish.

Inside there was the formed plastic shell you would expect to find. Build quality was good and the fire or furnace portion was particularly well made.

I was impressed. No idea how much this cost of course, but it certainly looked the part.

wood fired off grid hot tub
wood fired off grid hot tub

Building the Fire

Apart from the fact you are on your hands and knees trying to light a fire, then stocking up the wood, keeping it going long enough to heat up, it wasn’t that bad. Yes, it was a hassle and not like pressing a couple of buttons on your air source and coming back an hour later.

This was involved!

With the fire roaring it was time to monitor the temperature – with the floating “thing” also known as a thermometer.

The Heat Up Time

The very kind owner or custodian of the property had clearly built a fire and heated it up before we arrived as it was holding at around 34C or 93F when I opened up the tub. It was going to be interesting to see how long it actually took to get to temperature.

I did build quite a big fire using some big logs but was pleasantly surprised that the tub actually got up to around 39C or 102F in about 50 minutes – not bad at all. This is much quicker than you can do on electric, and is comparable to propane or natural gas and my big air source heat pump on a good (warm) day would just about do that too.

Pretty impressed with the heat up time to be fair although this was not from cold of course.

wood fired off grid hot tub

Checking the Temperature

With the lack of electricity, there wasn’t even a battery powered thermometer so we were going old school relying on reading the good old mercury. Not too much of an issue apart from the heat loss every time you open the cover to check – not the most convenient of ways of checking the temperature – especially if it floated into the centre of the tub and you needed to fish it out. I much prefer looking at my App or even the Topside control on the wall….

We got to temperature and the tub was ready for us to get it. I must say, I’m a bit funny about getting into other hot tubs now, especially communal / rental ones so I left the actual “testing” to my kids and the other members of the family.

Localised Heating

The first thing that they noticed was the localised heating around the area of the fire. Pretty obvious I guess.

The principal that they use to heat the tub is based on convection currents. Warm water rising to the tub of the tub drawing in cooler water to the heating cavity. However, according to my “testers” there were hot and cold parts of the tub, it was not uniform.

Also, the actual vents where the hot convection currents came out of got incredibly hot – like “going to burn you if you touch them” hot. This off grid hot tub is interesting to say the least and could definitely leave its mark, on your leg…….

No Temperature Regulation – Overheating!

What I hadn’t thought about to be honest was what happened next. I guess with a regular hot tub and our DIY built tubs, we have a thermostat that is controlling whatever kind of heating we are using.

We can get up to temperature then regulate things so it actually remains at that temperature.

However, with this off-grid, wood fire hot tub, there was not regulation of heat. As time went on and the fire continued to burn, the water got hotter and hotter. It continued to heat and the point at which some of the “testers” called it a day, it was up at 44C or 111F – far too hot for me!

What is pretty clear here for the off grid hot tub was that if you have misjudged the size of the fire, this thing was going to continue to heat and heat – you could actually end up scalding yourself! I’m sure you would be getting out before that, but it is seriously hot in the mid 40s for a Hot Tub.

The “testers” called it a day and we let the fire go out.

wood fired off grid hot tub

[billycrotty]

I'm building one of these with your block type system but with a log burning hot tub, Iv built the mosaic block built tub I decided against the fancy gunite jets as it went against the point of keeping the cost down and making it a natural experience, I will have just air jets that iv built in and lighting, it's next to a natural pool ( David pagan butler method ) that cleans itself so I aim to just circulate the water between the two using a submersive pump that pumps 250ltr a minute so it takes no time at all so empty and re fill when required. I'm using a log burner that I had anyway as a heat source.
Personally I'd rather do than sit in basically bleach but I'll put a video up of when it's done, I know one thing being a tree surgeon with access to lots of wood I'll be happy when I don't have an electricity bill that falls through the floor when it hits the mat!!
That's why people are giving hot tubs away left right and centre or scrapping them!