Introduction: DIY Wood Fired Cedar Hot Tub
We recently quit our lives in the city to live off the grid in the mountains of Idaho where we will be building an off grid home from scratch (check out our blog and adventure here!). Since building a home will be taxing on the mind and body, we decided to first take on a smaller project that would allow us to relax our sore muscles from home building, which was building a wood fired cedar hot tub!
Why a wood fired hot tub?
We are off grid, so electricity is limited. We do plan to have a full solar setup in the future, but right now, our only electricity comes from a generator when we choose to run it. We could go with a propane system, but why do that when we have endless fuel in our big backyard?
Why cedar over another material or tank?
We were going to go with a low-budget "cowboy" hot tub, but we were intrigued at the idea of building with cedar. We thought that this would look a little more classy, last longer, not to mention be one heck of a fun project, and it was!
Join us in our series!
Since cedar hot tubs can cost anywhere from $3,000 to $7,000, we thought it'd be fun to document our project for others that may want to do something similar (view original series). In the end, including the stove, we spent somewhere around $850. Not bad! You can find a list of tools you will need to do this project here, and for instructions, keep on reading!
Step 1: Find Source of Affordable, Clear Cedar Boards
The most difficult part of a DIY cedar hot tub is finding an affordable source of clear cedar lumber. You don't want any cedar with knots for your hot tub as these can blow out and cause a major leakage! That said, clear cedar (#1 grade) is expensive and most lumber yards don't stock it, so it's somewhat rare to come by.
We were able to find a lumber yard on Craigslist that had an abundance of cedar, but it was seconds and grade #2 which means that it was pretty knotty. With permission, we were able to sort through the pile to find enough clear lumber for our project (clear lumber for staves and floor of the hot tub that is). Sorting lumber is NOT OKAY with many lumber yards, so please ask before you sort!
We knew our stave size and floor size going into this project, but we can't give you exact dimensions because that depends on the size of lumber available to you and the size tub you create! Our tub is 5' in diameter and 3' in depth.
We also bought extra lumber (with knots) for the seats, fence, and even for hot tub accessories such as steps and a drink holder.
Step 2: Cutting the Staves
The first plan of action is to cut the staves of the hot tub. You will have to calculate the dimensions of each stave based on the size of lumber you're using and also the circumference of your tub. Also keep in mind that you'll be attaching the staves to the hot tub floor using a dado joint, so that will decrease the inner circumference of your tub.
When planning out your staves, try to get the most out of each board. Think about the order that your cuts need to be in so that you can use as much clear cedar as possible! We used a cross cut saw and a table saw to make these cuts.
Step 3: Stave Joinery
The most important part of this build in our opinion is the stave joinery. Listen up! If you are careless with this step, your life will be a living hell while you try to get the tub to seal up!
Bead & Cove Joinery
For the joinery, we went with a canoe joint, or a bead and cove joint. You'll need a bead and a coving bit to complete this step. Our stock was 1.5" thick, so we went with 1/2" radius bead and cove bits. This left a small shelf on the staves to allow the joint to seat properly. You can do this with your own router.
You'll need to run each board four times total... twice on each side to complete the full joint.
If you're left with a lip on your joints, as in they aren't completely round, you can use a planer to smooth the joint.
In theory, if your joinery is done correctly, the cedar should swell nicely which will allow your tub to hold water.
To attach the boards to the floor we used a dado joint. Read further to figure out what depth to create this joint at. You'll want this joint to be extremely snug on every single stave. There are various ways to make this joint but we chose to do it on our table saw. Because you want this joint so accurate and so snug, it's wise to check each joint for fit to make sure you have consistency throughout. You may want to jig your table saw for accuracy.
Step 4: Building the Floor
We built the floor out of cedar that was available to us which was 1x6 v-groove tongue and groove cedar. We don't recommend v-groove if you have the option. Many commercial cedar hot tubs use 2x6 stock which may be more ideal if it's available to you.
We did the same thing that we did for our staves - we positioned the lumber so that the entire floor consisted of clear cedar. You'll want to use a guide to make a circle in the diameter of your tub which for us was 5 feet.
We used 4x4 cedar for the floor joists of our tub - two 5' in length and two 3' in length. We spaced these equal distances apart.
For the dado joints as mentioned in the previous step, you'll want to cut these at a length that in theory gives you the perfect number of staves to complete the hot tub rather than needing half of a stave to complete the job. Watch the video to figure out how to come to that magic number for the depth of the dado joint - but in the end, you may be off anyways as we were in which case we had to get crafty with our last couple of staves!
Once we had everything in position, we used a ratchet strap to hold the floor in place while we went around the circumference with a jig saw.
Step 5: Hot Tub Assembly
The staves are simple to get on - use a dead blow hammer to gently tap the staves in place. Ensure that each joint fits nice and tight. In this step, patience is a virtue!
Not Enough Room for A Full Stave?
If in the end of your assembly, you discover that you need a partial stave as we did, you can do some trickery as we did in the video. We ended up cutting a stave in half and then creating a tongue and groove joint that attached to the second-to-last stave.
Cable Tension Bands
To hold the tub together, we opted to use a 3/16" vinyl-coated cable which shouldn't cause any harm to the wood. We purchased two clamp sets for each cable (we did three of them) to give the ends a nice finish. We attached the two ends with a stainless steel turn buckle
TIP: Use ratchet straps to hold the tub tightly together as you create your cable bands. Aim to have the turn buckles tightened about half way in the end. Your tub will continue to swell as it absorbs moisture, and it may also shrink in the sun if left out for days.
Step 6: Benches & Plumbing
For the benches, we used leftover 2x4 #2 grade cedar for the legs assembled as a square, and then leftover staves for the seats. Knots are fine for benches.
Our bench was designed off a hexagon shape, but we only completed four sides of the hexagon. The longest length of each bench is equal to the radius of your hot tub. The angle of the seat lumber should be 30 degrees on all sides.
We recommend using stainless steel hardware to avoid corrosion which is pricey but worth it.
The start of our plumbing is a simple push-style floor drain. We used a 90 degree pipe coming out of the drain and then attached proper fittings so that we could attach a garden hose to the tub for when we're ready to drain it. We also used a ball valve as a backup measure and we're happy we did, because our floor drain leaks! This is likely because of the drain we went with, not error on our end.
Step 7: Filling the Tub
Filling the tub is extremely straightforward, especially if you are on the grid and have endless water! That’s not the case for us… we’re completely off grid without a water source yet so this step was complete misery.
We had to keep out tub filled for three full days for the leaking to stop… but it leaked like crazy the first couple of days. This is normal.
Because we are limited on water AND impatient, we decided to caulk the tub with a marine-grade clear caulk. This did help the tub retain enough water to swell but we’re unsure if we actually needed it. We also weren’t confident in our joinery (which is why we said to be patient with it and do it right) so this was a backup measure for us.
Step 8: Adding the Wood Stove
There are many options for heating the tub at this point. We chose to buy a used stove from a hot tub company off of Craigslist. These don't come up often, but they do come up, so look around!
Attaching the submersible stove was very straightforward, but we did need to attach it well since it is extremely buoyant.
Our stove came with 6' of stove pipe which allows the smoke to exit well above our faces!
Do some research on buying a submersible wood stove, or you can find an external wood stove to plumb into your hot tub. At this point, you can probably go with a propane or electric system as well depending on if you're on or off grid, and what your personal preference is.
We WERE going to create our own external wood stove out of a washing machine drum and an old truck radiator, but decided to go the classy route instead.
Step 9: Enjoy Your Hot Tub & More Tips
Now that all the hard work is done, you get to relax! Our wood stove fired up extremely easily, and we're able to heat our tub from 65 degrees to 102 degrees in about 1.5-2 hours. Maintaining the temperature is a breeze as the stove is easy to shut down when it starts getting a little too warm.
More Tips & Tricks (Updated Regularly)
For more tips and tricks that will make this project easier, be sure to visit our official DIY cedar hot tub videos series page. As questions come up about this project, we try to answer them there so that we can consolidate our Q&As in one place! Also, read a blog post on our first soak (one of the most rewarding experiences ever).
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Hope you enjoyed this tutorial! Let us know of any questions you may have!