Introduction: Hot Tub Solid Fuel Water Heather

About: Engineer by trade, keen DIY expert who loves building things out of scrap - dedicated family man who loves to involve the kids with projects

My daughter woke up one morning and said "we should make something to heat the hot tub by burning wood" challenge accepted!

Supplies

First we made the first prototype out of some old reclaimed 15mm copper pipe with solder fittings.

Step 1: Cutting and Soldering

We sized the heat exchanger (or copper pipe) to fit out BBQ tray. We cut and soldered the piping to give a good surface area for the flames to warm the water.

Step 2: Connecting Up

We connected the heat exchanger to some hosepipe and a submersible water pump (that we already had for emptying paddling pools) with a temperature rating of 40deg. The water pump is on the colder side of the system, i.e. pressurising.

Step 3: Lit the Fire and Tested

The system worked well for about 2 hours and then the solder failed

Step 4: Upgrade to Compression Joints

We upgraded the design to utilise compression joints, we also shaped the heat exchanger to sit over the fire rather than below, this made it much more efficient and we've now used it several times.

Step 5: Safety Notes

Obviously having an open fire at ground level is dangerous, so we put the tray in our BBQ and put is near a wall so it is protected. Also - it is important that the system is manned at all times, should the pump stop for any reason or the hose have a blockage or kink the system will overheat.