Step 1: Build the Heat Exchanger

Picture of Build the Heat Exchanger
The heat exchanger is basically a coil of copper tubing that spirals up the inside a vertical chimney. We're trying to get as much heat from the fire as possible, including the hot air and smoke that rises up from it.

We made our heat exchanger out of 3/4 inch tubing, various fittings for the ends, and 12" diameter cylindrical sheet metal duct. The whole thing ended up being about six feet tall. Click through the photos to see the exchanger under construction. Whit coiled the tubing, stuffed it up into the duct, and then brazed the connections onto the ends.

Whit says the copper got work-harded as he coiled it, so that first step was more annoying (and resulted in a less-regular coil) than we expected. But it worked just fine.
j2bz6997 years ago
how did that sureflow pump work? what was the GPH?
greatpanda7 years ago
So...how did the components handle the salt? This is probably the best thing you could possibly have done with an inflatable hot tub!
Joshld7 years ago
Very nice! About how long did it take to get up to temperature?
nagutron (author)  Joshld7 years ago
It took about two hours, since our fire wasn't quite big enough, and the lack of wind screens meant that a lot of the heat was blowing out from under the exchanger. Under ideal conditions, I think it could have been as little as 30-40 minutes.