Cold Water Swim Training: DIY Pool Heater for Triathlon
How a wood-fired DIY contraption raised pool temperature from 15°C to 21°C to make swim training possible.
Braving 59°F (15°C) water calls for creative solutions. In a chat on the Stemma Sports channel, athletes share the behind-the-scenes story of Frankenstein, a homemade drum-and-copper pool heater built to beat the cold.
Swimming in freezing temperatures is one of the toughest challenges for endurance athletes. When water temperatures plunge into the 59°F to 61°F (15°C to 16°C) range, maintaining consistency and volume in swim workouts becomes nearly impossible without some form of heating, especially during stretches of continuous rain and little sun.
The contraption: The 'Frankenstein' heater
To make training sessions feasible in severe conditions, the solution was building a homemade system nicknamed Frankenstein. The rig was constructed from two welded metal drums, internally fitted with a 65-to-100-foot (20 to 30 meters) copper pipe coil. The system pulls ice-cold water from the bottom of the pool, circulates it through the copper coil heated by a wood fire, and returns it warm.
To speed up the process and boost the burning of dry wood, a blower fan was installed at the rear, ensuring a steady flow of oxygen into the combustion chamber. The effort, however, is nonstop: it requires continuously chopping firewood and feeding the furnace to sustain the heat.
From 59°F to 70°F: The water temperature boost
Although a conventional heat pump works well on sunny days, it loses efficiency when overcast skies, rain, and prolonged cold roll in. With the makeshift heater running at full blast, the pool temperature climbed from a frigid 59°F (15°C) to roughly 68°F–70°F (20°C–21°C).
While it still takes mental grit to jump in, that 68°F to 70°F (20°C to 21°C) range makes it possible to complete scheduled sets without paralyzing thermal shock, showing just how far an athlete will go to never miss a training day.