I BUILT ONE
It's an 8'x8', cinder block, concrete floor, painted with pool epoxy paint, complete with skimmer, pump and sand filter. My cousin welded me a homemade version of a snorkel stove (aluminum) and it worked... "great". I say "great" and not GREAT! because there are some issues:
1. I didn't account for the stove floating and I have no way to attach it to the tub. I ended up constructing a table with 20 gallons of concrete in the base to tie the stove down to. Worked fine but all the "fixtures" to attach the stove to the table are not aluminum. These points created rust and rust is hard to deal with in a hot tub.
2. Takes a while to heat up. 880 gallons of water with the snorkel stove AND a "bubble thermal cover" takes about 8 hours to go from 45 degree water to 100 degree water. This pretty much means it's a Saturday only heater. I work in my shop on Saturdays so when I go out early and build a fire in my shop, I would also build a fire in my snorkel heater. That evening it was nice!
3. Just an FYI, it's true what you read. You need to circulate the water to heat it up. I would burn my heater for 3 hours and the water around the stove would be great. The heat would never transfer further away from the heater until I turned the pump on.
In the end, I've taken the snorkel heater out permanently and we use the 8'x8' tub as a "dipping pool" in the summer. Works great.
That being said, I'm investigating getting a stock tank, putting a coil stove underground (I live on a slope), putting the tank on top and filling up the area around the coil with gravel. The coil will be in a bricked up area to build a fire in but the gravel all around will allow (hopefully) for radiant heat traveling up. Maybe the coil can heat the water and the heat transfer from the gravel can help retain the heat. Anyone have any thoughts on that?
