Gas/Wood heated Hot Tub

[Ashley Burton]

Anyone done this?

I'm tempted to get a hot tub, But don't want the water to be heated by mains electric.

I would be considering to use a circulation pump to get the water upto temperatue more efficiently.

I understand that the water wouldn’t be instantly hot.

 

[julianf]

My friends daughters swimmng pool is heated from a boiler running on biodiesel...

Basically any device for heating water will do the job - you just run a heat exchanger to your pool circuit.

 

[Wendelspanswick]

I've seen pictures of a hillbilly hot tub, basically 2 propane tanks, one on top of the other. The bottom one is a woodburner and the top one acts as a water boiler with pipe work to the hot tub.

 

[Ashley Burton]

I've seen pictures of a hillbilly hot tub, basically 2 propane tanks, one on top of the other. The bottom one is a woodburner and the top one acts as a water boiler with pipe work to the hot tub.

Sounds good!

I like hillbilly ideas if they work

 

[gaz1]

depends on if you want the stove inside of the hot tub or external to the hot tub theres plenty of versions out there even homemade ones including hot tubs

 

[Ashley Burton]

depends on if you want the stove inside of the hot tub or external to the hot tub theres plenty of versions out there even homemade ones including hot tubs

View attachment 136047

Would prefer outside personally

 

[gaz1]

homemade or bought hot tub stove

 

[Ashley Burton]

homemade or bought hot tub stove

Most probably built!

 

[gaz1]

then you want a small stove that can fit a back boiler into it or a medium size system that can also do the same

otherwise its a snorkel stove fits inside of the hot tub

 

[Blake's 7]

Have a look at this - https://www.woodwaterstoves.com/

"An Internal Wood Fired Heater sits inside the hot tub or pool and is mounted to the side wall. It is a stainless steel fire chamber that uses a very effective “rocket stove” principle to create a powerful fire."

Would a boiler stove with pipes connected directly to the tub work?

 

[gaz1]

sorry its just a firebox with flue stuck on end of it

though its not your quote its not a rocket stove either as the rocket stove destroys the top plate on them

 

[armalites]

Went in one in Alaska in the middle of winter, was just simply a firebox in the water. Worked surprisingly well

 

[addjunkie]

Anyone done this?

I'm tempted to get a hot tub, But don't want the water to be heated by mains electric.

I would be considering to use a circulation pump to get the water upto temperatue more efficiently.

I understand that the water wouldn’t be instantly hot.

I gave this some though, then went and looked at one at a shop. Basically a stainless fire box in the water. But after researching care and maintenance of hot tubs for our holiday let project we were put of by the ongoing maintenance to keep it clean and useable.

The one at the shop on display had a bit of slime wasnt nice. Then went and looked at another place. In winter...thick black slime.

 

[julianf]

As I mentioned before a stainless heat exchanger would be the solution.

Pretty much all boilers of any kind will be made from mild - which will rust.

A closed circuit (vented) will become deprived of oxygen fairly quickly, whilst the tub itself will never do so.

So you keep your mild steel on a closed circuit, depleted of oxygen, and transfer the heat to your hot tub circuit.

For testing you could use a standard flat panel exchanger but it probably wouldn't last so long before getting blocked with rubbish (hair etc) from the tub. Pool exchangers have much larger ways.

Once you have an exchanger you can pretty much use any heat source with it.

 

[pedrobedro]

Would using a heating coil like domestic hot water system work instead of having the tub water circulating through the boiler.

 

[gaz1]

 

[RonA]

Anyone done this?

I'm tempted to get a hot tub, But don't want the water to be heated by mains electric.

I would be considering to use a circulation pump to get the water upto temperatue more efficiently.

I understand that the water wouldn’t be instantly hot.

Had a similar problem with the grandkids paddling pool in the garden.
My combi boiler is in the garage, just fitted another outside tap but from the boilers DHW outlet & ran the hot water out to the pool with my garden hose.
RonA

 

[Exuptoy]

I have one of those inflatable Lazy Spas. It comes with an electric 'egg' pump/heater which is connected through the side wall of the pool but I made an adaptor for my kitchen tap which allows me to remove the tap head and fix this adaptor then fill off the combi.
A damn sight cheaper than using the electric heater to bring it from 14deg up to 40'. I fill it from the boiler which is pretty much straight in at 38 degrees then use the 'egg' to keep it topped off. Beware though, using it when it is very cold outside still uses an inordinate amount of electricity to keep it topped off.

 

[julianf]

Would using a heating coil like domestic hot water system work instead of having the tub water circulating through the boiler.

Ive tried that kind of stuff (heating drums of oil with scavenged coils from DHW tanks) but, whilst it works, the heat transfer isnt great.

Your heavily insulated, small volume DHW tank takes a fair while to heat from a boiler - i wonder if a coil would even keep up with the losses from a hot tub?

You would also need the coils "somwhere" and they take up a fair bit of space. Have them in the tub, and you would be in a conflict between running them hot enough that you would get good transfer and too hot so as to be a (mild) danger to the occupants.

I had stacks of the coils from a project, but i scrapped them last month - i didnt get a lot for them, and the OP would have been welcome to them, but i still dont think its the best of ideas.

If you look at the stats for a small flat plate exchanger the transfer is just so much greater than in-tank coils. Even if you just used stock FPHEs and changed them every time they got blocked, i still reckon it would be a better idea. YMMV : )

 

[FergalFarty]

A farmer mate of mine made a redneck hot tub out of a large plastic cattle feeding bowl (about 8ft diameter by 4ft deep). The water is heated by passing it through some scrap domestic radiators welded together and suspended over a fire pit. There is also a pump to circulate the water. It works very well, a bit too well if the fire is roaring.

If you attempt this, don't forget to flush out the radiators first unless you want brown water in your hot tub!

Fergal