Here in the UK it's been a great summer and I thought it would be good to relax at the end of the day in a nice hot tub. Trouble is they are quite expensive to buy and run and you need power and chemicals and really how many times would you use one. So I decided to build a low cost hot tub which can be run off grid and can be used quick and cheaply to have some fun.

Step 1: Materials

Knodd 40L bin with lid from your favourite Swedish bin emporium. £15 25 m 10mm micro bore central heating pipe from any plumbers merchants. £ 40 Kids paddling pool - I got a 1.9 m pool from Argos at the end of the season for £30 Aquarium 8mm tubing for pumping the water round your coil. 12v pond or bilge pump to circulate water. 12v power source - a car battery is ideal .

Step 2: Construction

The beauty of this is that it is so easy to make. We only need to construct our heat exchanger inside the metal bin in order to get tubbing! If you go with the Knodd bin you will see that it is tapered. This allows us to use it as a nice former for our heat exchanger. Start by drilling a hole in the side of the bin and insert the end of the coil from outside to inside the bin. Then start turning the bin smoothing the coil tight against the outside of the bin. After a while you will have a lovely shiny heating coil.

Step 3: Get Ready to Soak

Now you have your lovely coil you need to get it inside your bin. Since it is tapered you can take your coil and slide it inside the bin with one end poking out of the hole that we drilled to start. The top end you need to drill another hole and poke the other end of the coil out. You now have a cool portable hot tub heat exchanger. Now with a couple of flexible plastic tubes on the ends of your pipe you are ready to fire up your hot tub.

Step 4: Fire in the Hole

Now we are ready to crank up your hot tub. Fill up your hot tub with a hose - the one I had was around 700 litres and took a couple of hours. Get your pump and put it in the pool, connect the outlet of the pump to the bottom pipe from your bin - this is the hottest part of the burner. The outlet just flows back into the pool via your return tube. Careful it could be hot ! Get a nice hot fire going - your pool will heat up in around 4 hours if you keep your fire hot . Once it is up to temperature (I like 40c) you can damp the fire down with the lid supplied .

Step 5: Find Your Perfect Spot

So the benefit of this tub is it is portable - you can put it anywhere you have some water and a flat space - I have the perfect spot under my cherry tree. You can see the pool and pump fits inside the bin so its easy to transport. Enjoy with your friends our your favourite drink - mine is an Innis and Gunn :-) Have fun !