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DIY: Constructing a Wood Fired Hot Tub

By azjunk | DIY

Jun 14

Building a Heated Jacuzzi for Your Enjoyment Pleasure

diy hot tub

5 SIMPLE STEPS FOR A DIY HEADTED HOT TUB WITHOUT A PUMP

Just because you don’t happen to have an in-bath Jacuzzi tub in your master bathroom doesn’t mean you shouldn’t be able to enjoy all the benefits of the good life.

It’s simple to build a heated hot tub fueled by a simple wood-fire by yourself.  Keep on reading to learn how you can build one of your very own DIY heated hot tub – for (hopefully) less than $1,000 – a fraction of what you would spend trying to install one of those fancy Jacuzzi tubs in your home. We’ve hauled away 100s of Jacuzzis from Phoenix homes to know that these tubs are a short lived luxury in the Valley of the Sun. This DIY method will allow you to construct your own in a weekend, and when you’re ready to move on the disposal will be minimal.

Stuff You’ll Need

  • 1 100-gallon tub or large stock tank
  • A ton of water
  • 30% hydrogen peroxide solution
  • Fast-setting concrete mix, gravel
  • About 20 feet of copper tubing – diameter between ½ inch and 2 inches
  • 1 x ¼ steel bars
  • A power drill
  • Push-to-connect fittings
  • Silicone-based or other waterproof caulk
  • A large tarp, preferably with fastenings like stakes and cords

Step 1

setting foundation for hot tub

Place your tub and set the foundation. This will entail placing your tub or stock tank on the ground where you want it. Trace the outside of it with a stick or chalk, then dig within that area about 6-10 inches into the ground. Pack down a couple of inches of gravel, then pour the concrete so your hot tub sits just above the surface of the ground.

Depending on how quickly you want the job done, use slabs or forms to support the tub and poor the concrete around them. Alternatively, you can make a thick concrete foundation for your tub to sit on.

The most important thing is to make sure the tub doesn’t sink into the dirt or get punctured.

Step 2

heating hot tub
heating coil

Bend your copper tubing into a coil between 16 and 24 inches tall.

Leave about four feet of uncoiled tubing on either end of the coil.

Bolt steel bars around the coils to act as supports. Drill holes in the bars – a word from captain obvious here: don’t drill holes into the the coil .

The coil will act as your firepit. As a result, leave about a foot in diameter for you to place coal in and stand firewood up against the coils.

Step 3

hot tub with connections

Drill two holes reasonably close together in the side of the tub, put the fittings through the holes, and seal with a sturdy waterproof caulk.

Now you can insert both free ends of the copper tubing into those fittings.

Step 4

filling outdoor hot tub for bath

Using a garden hose or whatever water source you have, fill up the tub and give it some time to heat to your desired temperature.

Step 5

Enjoy! Isn’t physics amazing?

Upgrade Your Tub

Tips for making a sturdier base

You can always rely on the gravel and concrete base, but with just a few added extras, you can create a base structure that is going to last longer overall. After adding a strong base you can also add concrete anchor posts to support an upper deck. This is what you can build above your base structure. The optimal part of adding anchor posts will allow you to add square or rectangular-shaped wooden beams that intersect.
Heated Jacuzzi sturdier base

In between these beams will be enough room to cut inner support beams that are screwed into place. These beams should touch the concrete base, so the weight is distributed over the concrete and gravel mixture you’ve laid out. Just make sure the structure is totally level which will need additional leveling when you insert your anchor posts. Choose a wood that will last longer outside, so redwood and cedar make excellent choices.

Enclosing your hot tub for insulation

If you’re using a metal tub, this is good for keeping helping to keep water ‘nice and hot’ but it will also act as a heat sink. Just like the heat sinks used on LED lights, the tub will radiate heat anywhere the metal is exposed. This is why it’s better to surround your tub with an insulating foil bubble wrap. You can find this at any hardware store and attach it to your tub with heating duct foil tape.

After this, you can add strips of redwood or cedar around the outer edge of the tub to help keep that heat from escaping. The only way that heat will end up being released from the water is through air condensation and steam. I recommend that you add a thin strip of bendable restraint light strap. This can be screwed into the backside of your wooden strips at the top and bottom.
hhot tub wooden insulation

The good part is that you can have one continuous strip that stretches all the way around your DIY hot tub. You don’t need to allow gaps between each strip since the light strap is on the inner edge. When it bends around corners it will appear natural. Unless you want to use a 45-degree angled cut on each plank edge, you can make each plank appear to butt together much closer around all of the rounded corners.

To attach this around your hot tub, use a heavy-duty Velcro on the starting and ending points of your wood plank wrap. Line up the fuzzy and scratchy sides so they overlap each other and are only attached on the inside. This way, the wood wrap can be removed anytime and is essentially attached as a cosmetic ring around your insulated hot tub. To take off this wrapping ring, all you need to do is pry the Velcro attached edge open using a butter knife.

Building a better heating coil system

I came up with this idea as an afterthought when I told you about the heating coil ring. The cool part of using a wood-burning fire to heat the coil is to get the maximum amount of heat circulating in the tub itself. Think of this coil ring like one of those crazy Radio Shack hobby experiments. It’s really a simple matter of simple induction heating that helps create your DIY hot tub heater.

The rising heat of the fire causes heat to rise, so you’ll have a fire powered hot tub in return. Essentially, the cool water in your coil tube is heated and will naturally arise in the process. Cooler water is then pulled from the lower part of the coil and the process repeats creating a DIY hot tub with jets. This creates a constant water vacuum pump. But that doesn’t help the wood-burning problem very much.
heating coil system building process

Whenever the wind changed, I got smoke in my eyes and made my hot tub experience start to feel like I was that unlucky guy who got caught by the cannibal tribe! Yes, this is the perfect kind of fire heated hot tub that won’t smoke you out, but will give you excellent heating results.

How to upgrade your heating coil

heating coil on drum

I started thinking about those outdoor space heater towers you see in outdoor restaurants and thought, hey wouldn’t that be great if that could go inside my heating coil. You need it to be hot enough just like a burning wood fire, but sometimes that flame was just too hot. It also made my copper coil look ugly with all of that carbon char and buildup. So I started to look at ideal heaters that could work for my homemade Jacuzzi

convection heater for hot tub

Mr. Heater Corporation Convection Heater

It turns out that I found a neat and cheap little heater that fits perfectly inside my copper coil. This is a standard convection heater and can pump out 30,000- 80,000 BTU per hour using any connection of propane gas. It’s about the same size as any kitchen-sized garbage can measuring 16.6 x 15.9 x 21.8 inches in all. They also have a smaller model that only 13 x13 x14 inches, but this might be too small for your hot tub heating needs.

I almost forgot to add that this convection heater has an adjustable setting to increase or degrees your propane flame. This will help keep your tub at a constant temperature all night long!

Building an optional heat-shield

Don’t say that I didn’t warn you but space heaters and heating coils can get pretty hot! Even for Captain Obvious to repeat himself in Family Guy grandeur, If that heater hadn’t been exposed- you wouldn’t have gotten burned so easily!’ Well- I’m telling you now that it’s not a bad idea to build an extra shield around your heater to protect pets, kids, or curious chickens who might be getting too close to your backyard hot tub setup.
Heated Jacuzzi heat shield

Here’s what you can do to prevent a towering inferno scenario. I recommend that the easiest way to absorb that heat and still get protection on the outside of your heater is to build a brick ring tower around your heater. The bottom should be stacked so you have open airflow under the tower and so you can still adjust the heat dial. Better yet, use cinder blocks around your heater base so that only the heated area is enclosed.

You can buy decorative bricks from any Home Depot or garden supply center and build a rind around your heater. Here is a good DIY instruction guide for building an enclosure for a gas heater. You can use your imagination where it needs to have a base that allows air to flow thru it like a chimney. You also want to have good airflow so the bottom of your propane heater isn’t getting overheated.

Aside from that, this is how you can make a homemade hot tub that has some safety additions and heating improvements.

Maintenance

Once you’re all done, cover up your homemade hot tub with a heavy-duty tarp to prevent leaves and insects from getting in. Keep it closely tucked down the sides of the tub. You can weigh it down with extra bricks or large stones if you don’t have stakes and cord to tie it down with.

In order to prevent the water from getting funky, add about a third a cup of hydrogen peroxide (available in diluted concentrations at most grocery stores, drugstores, and supermarkets) about once a week. This will prevent bacteria growth.

If you use it every single day, you’ll want to change the water about once a week.

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