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Open Source Heater Design

This section will likely appeal to a very small number of you as it broaches the realm of wonkiness. However it is a personal homage to my late father Pertti Raty, one of the world's great sauna builders. Dad was a mechanical engineer and professional welder but above all, a lover of sauna. Over the years he designed and fabricated several unique wood burning sauna heaters that were ahead of their time. Now, exactly 20 years since his passing - a milestone that played a key role in the launch of Saunaist - I am pleased to be able to share some information about them. 

The Hotpert V1 - circa 1978

The Hotpert (hot + Pertti + expert) debuted in 1978 when my father partnered with Sauna-craft in Toronto to market and sell his novel heater. Its predecessor - and his first experimental heater - based on the same principles of thermodynamics was also the first heater I enjoyed in our Georgian Bay sauna that he built in 1975.

Dad was enamoured with the quality of heat that the old smoke saunas (savusauna) produced back home in Finland. Although they were largely relics of history by the 1970s he was determined to emulate the softness and depth of the heat they produced. Hotpert was the answer. 

The Hotpert was designed to accommodate hundreds of pounds of rocks,  - the secret of the old smoke saunas - but with the added features of heating speed and controllability.  Its most unique feature was its helicoidal heat exchanger, a spiral ramp at the base of the flue which provided for more efficient and robust heat transfer. 

The Hotpert V2 - circa 1986

When it came time to build our new family cottage in 1986, Dad's designs had evolved to include a hot water tank, albeit with a gap of an inch between it and the heater. This prevented the water from boiling and causing unwanted and/or uncontrollable humidity. Additionally it was built into a custom heater alcove within the sauna room that reduced the overall effect of radiant heat from the steel stove. Below are some hand drawn sketches of it prior to fabrication. 

The Hotpert V2 was built in 1987 and, thanks to its crematorium grade steel, lasted until 2021, just shy of 35 years (of constant use). Eventually the welding seams gave out and we had to have it replaced. That story below.

Hotpert V3 - circa 2021

All good things must end and so it was with the last sauna heater my late father fabricated. After 35 years she breathed her last fiery breath and lay down to sleep. Determined to replace her, I dragged her 400+ pound carcass into our little tin boat and then into my truck and hauled her to my buddy Johnny Silegren at Gatecrest Industries, a metal fabrication shop owned by Finns and fellow sauna enthusiasts. It was like a funeral procession. 

There I asked Johnny to build me an exact replica and with the carcass on hand and the scrawled designs above, he set out to work. A few months later I got a call that she was ready and together we lugged the magnificent beast to the cottage where Johnny installed it. 

At almost 500 lbs she was a handful, yet resplendent in her shimmering glory. We added a metal webbing on top of the main stainless steel shell that allowed for an extra 150 lbs of rocks to be piled on. In total my estimate is that she is 1,000 lbs in total. Some might say this is a bit excessive for an 8' x 6' sauna but Hotpert disagrees. 

The heat and löyly that emanate from her are exquisite and evocative of the smoke saunas of my youth. Deep and resonant heat that penetrates into the marrow of your bones. The softness with which it envelops you belies the readings on the thermometer (130C/266F+). The löyly is incredibly delicate as it dances around the sauna before embracing you with intimacy and intoxicating pleasure. Every time I feel her warmth I can sense my father's spirit in the hot mist and I am confident it will be another 35 years before my kids have the honour of overseeing the advent of Hotpert V4.

Hotpert Install.jpg

Hotpert V4 putting up a good fight. August 2021

Hotpert 2.1.jpg

Hotpert in place. Note the sausage hooks hanging above the rocks. 

Hotpert 2 top bench view.jpg

Top bench view. Note the alcove for the heater which reduces the effects of  radiant heat and guides the löyly up its sloped ceiling into the sauna room. 

Hotpert 2 firebox 2.jpg

Exterior view. The firebox can handle firewood up to 2 feet in length. 

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