How to Build a Wood Fire Hot Tub

Partridge Hill is Mark's escape from the city.  Located in the Berkshire Mountains you’ll find his log home nestled in amongst about 40 acres of pristine wilderness. Offering year round views of the surrounding beauty Mark decided that a hot tub would make a meaningful addition to the grounds and began researching the options.  Although almost all hot tubs in America are your traditional pvc / plastic tub style with integrated heaters and jets he wanted to go something with a more natural using only wood and stainless steel and landed on a traditional Japanese style soaking tub.  

Step one is to determine the site location for the tub.  Although he was tempted to place the tub in a remote area of the property, the team at Snorkel highly recommended proximity to the main structure to maximize use.  After installing he strongly agrees.  The location was chosen on the back edge of the lodge’s wrap around deck.  Ensuring the surface is flat and can handle the weight of a tub full of water (and people) is critical.  The location was chosen and the build began.

Setting up tub foundation
Part 1 - Space Chime joints 16”apart running against the grain of the tub’s floor boards.  Because the deck also had decking boards we set them up perpendicular to those as well.  The chime joints are set with the 4” side on the foundation and positioned so that they will not touch the drain.

Place the two bottom sections on top of the chime joints, make sure “This Side Up” faces up.  Again, the floor sections must be perpendicular to the chime joints so the floor will be properly supported. To keep the floor boards sung together, nail two wood strips across the center seam.  Offset the nails to prevent space from forming and increase stability.

Place bottom on chime joists and use a level to ensure bottom is level.  Make sure the bottom makes contact with the chime joists and if necessary, use wood shims. The bottom should overhang the joists by at least 1 ½”

On the tub bottom, apply generous bead of silicone to the recessed lip of the counter sunk hole.  Spread silicone and sealant mixture freely on the surface.  Put rubber gasket up against the fitting and insert fitting into hole from inside the tub.  Apply silicone to the flat side of the plastic nut and screw onto outside of the threaded end of the fitting.  Do not over tighten as expanding wood when the tub is full can lead to cracking.

Set the drain fitting adaptor and screw the threaded end inside thread of elbow and then thread into drain fitting.  Install stopper on the inside of the tub and make sure it runs continuously downhill.

Assembling the Hoops/Bands

Lay hoop pieces on the ground with two thread ends touching. Connect them by screwing in coupler nut.  Repeat for each loop. Install the lug by inserting threaded end of the hoop into narrow end of lug.  Slide washer on and thread nut on ½”  so hoops will fit loosely.

Apply lubricant on threads through backside of lug, emphasizing a large amount on the bottom hoop threads as these are the threads that will be under the most tension. Place one completed hoop around the base of the tub as it is easier to slide the first hoop up from the bottom.  The others can come down over the top.

To start, locate the four staves marked with chalk lines and two key staves and set aside.  Note that the staves with chalk are to be place around equal distances of the tub to aid in hoop placement.  The key staves will be used to fit in the final gap.  Stack the staves on the tub bottom to help keep the bottom in place as you work on it.   Erect fist stave over the seam between the two halves of the tub bottom.

Put on all full width staves first ensuring to place the marked staves equally around the perimeter to use as a guide with the hoops..  Use blue masking tape to hold staves together as you work on the tub.  This is very important, and be liberal with tape usage as pictured.  At first tape was used sparingly which resulted in the entire set of staves needing to be replaced two times. Staves should be touching one another with about 1/32”gaps (thickness of a credit card). 

The staves should be lined exactly up with the outer chalk line on the tub floor, not the inside line.  Use your mallet to lightly move the staves into alignment as you put them around the tub.  After the full width staves have been installed you will fit in the key staves.  The flat edges are to be pressed tightly together with the tongue and groove on the outside. 

If the gap for the key staves is two wide for them to fit snugly, then you must install the key staves in the gap against the last full width stave that was installed.  Remove two staves and move 1/16” between them and the adjacent staves.  If your initial gap is too narrow for key staves to fit, remove the first two full width staves that were installed and install key staves against the last full width stave.  Move one stave and then the next (3rd to be installed) 1/32” between the two.

Installing the bands/hoops
Assemble the bottom hoop around the base of the tub and slide it up.  Pull the lug and coupler nut away from the wood.  Use nails to rest the hoops on and support it on wood blocks to hold it all in place.  Hoops should be located at the follow measurements:
3’ stave: 4” (bottom), 14”(middle), 32” (top)
4’ stave: 4” (bottom), 14” (middle #1), 28” (middle #2), 44” top
Position the lug of the bottom hoop so that it spans the joint between two staves and is as close as possible to the midpoint. Remove slack in the hoop by tightening the nuts with a wrench. Repeat process with remaining hoops. 

Rounding the Tub
Rounding is completed through the repetitive process of 1) Pounding the bottom hoop/band to move the staves inward. 2) Tightening the hoops/bands and 3) Keeping the staves aligned so their tongues and grooves stay engaged.  You only need to pound the bottom hoop, don’t hit the middle or top hoops.  Do not over tighten.

Snorkle Stove Instillation

Place stove in tub and climb in it.  Bend the mounting brackets on the side of the stove to be mount to the tub to conform to the tub’s curves.  Hold stove in place with door opening 1” above the rim of the tub.  For Snorkel stove, set on combination of a fence board and board support.  Mark hole locations through the bracket holes.  Set stove aside and drill 5/16” hole through the tub at each mark.  Open mounting package and slip rubber washers onto carriage bolt until it touches the head of the bolt. Push carriage bolts through holes you just drilled.. Place stove back into position in the tub, running the carriage bolts through the holes in the mounting brackets.  Remove any supports before tightening the bolts then tighten the nuts securely.

Door Handle Assembly
Bolt the handle to the stove door.  The handle should be oriented so the grip is facing the end of the stove door and not the center.

Building the Stove Pipe
The hot tub needs at least 6 feet of stove pipe.  For galvanized pipe, insert one edge into the slot of the pipe and squeeze into place.  If you are using a stainless steel pipe with coating, simply peel off coating before assembling. To secure pipe, you can pop a rivet or install sheet metal screws at the joints using 3 fasteners per. 

Installing the stove damper
Remove the damper handle/pin from the damper.  Compress the spring on the pin and push the wide end until it compresses then turn the pin.  Use handle/pin to make an indentation in the pipe.  Make mark 12”up from non-crimped end and 90 degrees away from welded seam.  Drill hole for handle.  Insert handle into hole you drilled.  Remove damper handle and pound dimple into the pipe.  Push the spring on the handle back in place, insert the pin in the pipe and thread it into the damper.  Push the pointed end of the pin through the opposite hole.

Fence Assembly and Instillation
The fence is attached to the Snorkel stove by bolting it to the four mounting brackets facing the center of the tub.  The fence is attached to the store by four 1 ¾” carriage bolts and wing nuts.  Mark the 3 horizontal fence boards for vertical fence board placement.  Attach the vertical fence boards the the 3 horizontal fence boards.  Place the stove on the fence and mark and drill four 5/16” holes, two in the middle area of the fence and two at the bottom.  Mount stove using 1 ¾” carriage bolts and wing nuts.

Building the Hot Tub Benches
Determine the height you want each bench.  Set bench against the tub wall and measure the distance from the bottom of bench to the tub floor.  Take 2 supports and use 2 ½” stainless screws and center screws 2” from end on each support.  Screw two supports onto the front of the bench perpendicular to seat front.  Place bench on top of support screws to tub wall.

Building the Stairs
Attach treads to jacks, pre-drill holes for lag bolts. Attach rear rail support to left side of steps. Attach front rail support and railing.  Tag diagonal support before nailing.  Finally, screw diagonal support brace across rear of stairs.

Filling the Tub
Begin to fill your tub using a standard garden hose.  The warm water will help the wood to swell to seal up any leaks that may be present. After one day all leaks should be gone and you are good to enjoy the tub!

Credits and thanks:  Thanks to Snorkel Hot Tub for building an amazing product and providing great customer service.  Thanks to Ron Schulz for helping build the tub.  Thanks to Popular Mechanics for joining us on this journey!

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