I‘ve wanted a hot tub (or spa) for a long time. I’ve tried a hot tub several times (mostly when staying at a hotel or a B&B) and really enjoyed it. Honestly, who doesn’t like the idea of relaxing in hot swirling water. Maybe sipping a cold brew or a glass of white wine with your sweetie. Letting the bubbles and the steam carry away the stresses of the day…
But Dang!! Hot tubs are really expensive. I can’t see myself turning loose of $5000 to have a hot tub (I want one that much, and it might be worth it, but I just can’t see it). For a self-sufficient guy like me that leads to only one possible conclusion – “I can build one myself.” How hard can it be? Something to hold water, a pump or two, a heater, a filter, and some control mechanism(s). I can do this. I’ve got a machine shop. I can build anything. This is NO PROBLEM…So I got to work…
OK, so I could have started with a used hot tub. I know there are a lot out there. They aren’t real common out here where I live. I’m not opposed to rebuilding a used item bought for a good price, but it really isn’t as satisfying as building something from the ground up. So I started looking for information. How do you build a hot tub? Remarkably there is very little information on the internet. There is a story about someone who built a hot tub from an inflatable kiddy pool and a coffee machine for $35. The Solar Biz, and Island Hot Tub Company have some good information about using plastic stock tanks to build soaking tubs. There are people on Ebay advertising plans to “build your own hot tub.” I don’t know if they are really worth anything, but I hate paying someone for what should be free information. There’s one website advertising plans to build a hot tub, obviously using a plastic stock tank, but doesn’t say much about the plans. Another site has some information about a home made hot tub and options for heating it, but it looks like just a soaking tank. I didn’t want just a tank of hot water to soak in. I wanted a real spa. I want a filter so I don’t have to drain and refill the tub every few days. I want a heater and a thermostat so it stays hot all the time and it’s always ready. I want jets and bubbles so I can sit in swirling, massaging hot water. I want a cute blonde in a bikini in the hot tub with me…
Disclaimer – I am not a professional plumber, electrician, or hot tub designer. I am NOT recommending that you do anything described on this page. A hot tub is potentially hazardous (water + electicity). Any hot tub project you undertake needs to conform to NEC standards and must meet any applicable local, state, or federal requirements and standards. Do not undertake any such project unless you are highly competent in the necessary skills. I am not recommending any course of action, I am just describing my experiences for your information and/or amusement. If you kill/maim/injure yourself (or someone you care about) don’t come crying to me.
First, I needed something to hold the water. As mentioned above, there are several sites that discuss using a stock tank as a hot tub. I thought about building an in-ground tub and doing the concrete and tile work myself. I could, if I had several weeks of spare time. The plastic stock tank seems like a reasonable compromise.This is a 9′ dia. poly tank from Behlen Country. It seems pretty durable and is a comfortable shape. It’s bigger than really necessary for a hot tub, but it has to serve as a kiddy pool too.
We’ve had an awful lot of fun the past several summers with kiddy pools, and I don’t really have room for a pool and a hot tub. The 9′ tank will have to serve double duty. A hot tub for part of the year, and in the summer I’ll turn down the thermostat and it will be a kiddy pool (which the adults might get in sometimes). In the picture above you can see that the tank is sitting on a bed of sand that I put in as a base for the kiddy pools. I’ve leveled and smoothed the sand and it makes a pretty solid base for the tank.
With the tank sitting where I wanted it and level I started framing up around it to build a deck and enclosure (just like a real spa). The frame really isn’t supporting anything but the deck. The tank is designed to be free standing and to hold the weight of the water. Hopefully with the packed sand as a foundation the tank won’t settle too much when it is filled.After that it was time to start installing the hot tub type equipment. That was going to require cutting some holes in the tank. Made me pretty nervous. I don’t know how cutting holes for skimmer, jets, and suction fittings will affect the structural integrity of the tank. But I won’t find out unless I try…
It’s going to take a bunch of stuff to make a hot tub/spa. You’re going to need a pump (I used two), a filter (unless you want to empty and refill it every time you use it), a heater, jets, suction fittings, maybe a skimmer, some kind of control system (I decided on a timer and manual switches), and you will need to run the electrical supply through a GFCI. All that stuff could get pretty expensive.I bought almost everything on Ebay. There is a lot of pool/spa equipment for sale on Ebay. If you are a little bit patient you can get some great deals. The stuff I bought for the hot tub was on average about 20% of new retail price. Much of it was never used (some was old stock, but never installed).
The first thing I installed was the skimmer. This is a skimmer designed for a large above-ground pool (not the little strip skimmer usually seen in hot tubs). It’s probably a better design for the hot tub/kiddy pool I’m building. Besides, it’s the one I could buy really cheap on Ebay. The skimmer is a pretty big box and required cutting a big hole in the side of the stock tank. I would have liked to install the skimmer higher in the tank, but that would have required cutting into the rim of the tank (which is a major structural element) and I decided not to do that.
With the skimmer installed I started to lay out the locations for the suction fittings and the jets (the location of the skimmer was limited by the framing for the deck, everything else could be put anywhere).So, I made some measurements, did some planning, sat in the tub for a while…and started drilling holes. That was pretty tough. Take a perfectly good, brand-new, watertight tank and drill holes in it!?!
But, you can’t have a hot tub/spa without jets and you can’t have jets without holes to put them into. So, a couple of hole saws and I’ve got a tank with a bunch of holes in it. The high density polyethylene the tank is made of actually machines (saws, drills) very neatly. The holes look good and I think the arrangement of the jets will be very comfortable. Now to install the jet bodies.
I found two different kinds of jets on Ebay. I bought several like the one at the right. These came as complete sets (internals and bodies). They have a built in venturi to suck air into the stream of water to get bubbles. They are really nicely built with stainless steel eyeballs and O-rings between all the parts. I’m not going to add an air blower to my hot tub so I’m hoping the venturi’s will suck enough air through a passive system to get some good bubbles going.
I also bought a bunch of jets like the one at the left. These were just the internal part (no body to attach them through the wall) but were a lot cheaper than the ones above. I built the bodies (the white part at the rear) from regular plumbing fittings using my lathe and mill. It doesn’t give me any air injection, but it was a LOT cheaper than buying the jet bodies from a spa supplier.
I wound up with a bunch of jets and I’m installing 22 jets in the hot tub. Sixteen of the jets will be plumbed to the high-speed pump and will only be in use when someone is using the tub. The other jets will be plumbed to a lower powered pump to return water that flows through the filter and the heater. This pump will be run by a timer as well as manual control so that the tub will be filtered and heated on a regular cycle even when it isn’t in use. All of the jets are pretty plain. These jets just squirt water in, no “moto massage” “tornado” “waterfall” jets or other fancy stuff. I think it will be OK. The number of jets isn’t real large compared to the number of jets in a lot of commercial tubs, but I arranged them pretty carefully to put moving water where I wanted to be when sitting in the tub.
With the layout of the jets set and holes drilled I started installing the jets. I put in four banks of four jets (like the ones at the right) that will be powered by the high-speed pump and six jets that will be plumbed to the low-speed pump as returns for the water from the filter and heater. The jets even look pretty good in the tub.
I started installing some of the plumbing as I was installing the jets. I realized when I was installing the jets that are in pairs (about 9″ apart) that I would never be able to get the pipe between the jets installed after the jet bodies were inserted in the tank.I love working with the PVC pipe and fittings. I can get that purple primer on everything. You need something dyed purple? Just leave it near me while I’m working on PVC pipe fittings. I guarantee I’ll get it colored purple.
There’s lots of plumbing work to be done. Lot’s of stuff to connect. If there are any professional plumbers out there, please don’t look (or at least don’t laugh). I’m sure that a professional could design a much more compact and cleaner system. I used a lot of fittings and filled a lot of space. But, PVC fittings are cheap and I had the space. Looks a little busy, but I’ll bet it works. I’ll build a box around it and no-one will ever notice. There is some good information on Almost Heaven‘s web site about plumbing a hot tub. They are selling kits to build cedar hot tubs and I don’t know anything about the kits, but it was nice of them to put their instructions on the web. One of the owner’s of Almost Heaven emailed me and says that they actually do a lot of business providing parts and advice to people building their own hot tubs. I still haven’t done any business with them, but he sounded sincere and if I was doing it again I would definitely as them for help.
One of the first steps in the plumbing was installation of the suction fittings. I thought about building these myself, but I’ve read some pretty ugly stories about people getting trapped and injured on pool or hot tub suction fittings. So I broke down and bought two commercial suction fittings, each rated for 100gpm. I could have built them, but there’s a lot of engineering in these pieces and the money I might have saved isn’t worth the safety of my family and friends.
Even for someone as self-sufficient as myself, there are some parts that aren’t worth making yourself and that can’t be reliably found on Ebay. I bought some parts (thermostat, suction fittings, light housing, heater unions) from commercial suppliers. I bought most of them from Spa Depot. The service was good and their prices are great.
The two suction fittings and the skimmer are all T’d together into a 2″ line. With all three connected it should not be possible to cover any one of them and get trapped by the suction of the pump.
The 2″ suction line leads to another T fitting and 1.5″ lines to each of the pumps. The pump on the right is a 3/4hp pump (that I referred to earlier as the “low speed” pump). Output from this pump will go through the filter and the heater. This pump will be wired through a timer (as well as a manual switch) so the filter/heater run at regular intervals. The pump on the left is a 2hp pump that will be run from a manual switch and just feed the “hydrotherapy” jets.
The lower power pump (3/4hp) is plumbed into the filter (this is a 50sq. ft. Sta-Rite filter) and then into the heater and ozone injector. Although it isn’t a real clean/compact design I was trying hard to reduce the head (resistance) on the pumps. When I needed to use a 90° fitting I tried to use a “long sweep” fitting to reduce the resistance on the pump. Here you can see the 3/4hp pump and the valve on the suction line and another valve on the line leading away from the filter. There has to be a valve on both sides so that it is possible to change the filter element without draining the pool. Just to the right of the valve on the line away from the filter is the thermowell.
This is the thermowell. Although they are commercially available, I built this one from regular plumbing parts. The sensor (thermocouple) for the thermostat fits into the opening that is visible at the right of this fitting.
Downstream of the thermowell is the heater (from Ebay) and the ozone injector. I built the ozone injector from regular PVC fittings and a little lathe work. It is designed to use the Bernoulli effect to create a suction and draw air through the ozone generator. It would have been easier to just inject the ozone into the air intake, but I wanted ozone whenever the filter pump is running.
I‘m sure that professional plumbers or hot tub designers (and maybe many amateurs) who look at this picture will be astounded at the amount of plumbing around this hot tub. I was trying hard to reduce the head (resistance) to the pump (especially since this is going around a tub 9′ in diameter). I tried not to use any 90° fittings. You can see in this photo that I’ve used short sections of flexible PVC (spaflex) to make the turns around the hot tub. I could have used spaflex for all the plumbing, but it is really expensive (about 10X the cost of regular PVC) so I just used short sections of spaflex to make the turns.
With a little more time to work on the hot tub I finished the plumbing. Here is the larger (2hp) pump plumbed into the jets. There’s a valve in the output line so that I can clean the strainer basket. The 1-1/2″ line out of the pump goes to a T fitting and then each branch feeds a 1″ line that goes to the jets (still trying to reduce resistance and get the maximum rate of water flow).
I also finished plumbing the air lines (for some of the jets). This is the valve on the air intake. It’s home-made and not real pretty (although it looks better in person than in this picture). This is strictly a passive air system. The venturi’s on some of the jets will pull air in as the water flows through the system. I really didn’t want to mess with an electric air blower.
After the plumbing I started installing the decking. I’m using regular lumber (not treated) so I will need to use some sort of sealer/stain to protect the wood. It might not work where you live, but this is a very dry climate here and even untreated lumber will last many years.The untreated lumber is a lot cheaper too.
I set the deck planking at a 45deg. angle to the framework of the deck. That’s actually because it was easiest to put the support framework in at that angle. It’s just a lucky side effect, but it looks really cool.
When I get the deck finished the next step will be the wiring. If you’ve been waiting to see wiring diagrams or complete descriptions of how I wired the hot tub, I’m going to disappoint you. I’m not going to post wiring schematics, complete directions, or even complete pictures. This really is a potentially hazardous project and I won’t be responsible for injury to yourself or others because you didn’t wire things correctly. No offense intended, but this isn’t the project to start learning wiring with. If you are a pretty competent DIY electrician you will be able to figure out the wiring. If you aren’t, you need to ask for some expert help. Please do not attempt a project like this unless you are able to follow all local, state, and federal requirements regarding the wiring and are willing to make certain that your wiring is safe.
I hope that there are still some people reading this page (although it’s a long page and it has taken me a long time to get it finished). Over the Memorial Day 2005 weekend I finally “finished” the hot tub project. The deck isn’t completely done, and I haven’t finished the skirting, but it is functionally complete. You can see that it works just fine as a kiddy pool.
Part of the deck is hinged and lifts up for access to the pumps and filter.
The controls for the hot tub are in two boxes on the side, next to the steps. The right-hand box houses two switches that control the pumps and the heater. The left-hand boxes houses the thermostat and the switch for the light.
These are the two switches that control the pumps and the heater. Yes, that is a disconnect above them in the box. It is NOT the disconnect for the hot tub (although it would still function in that capacity). It is too close to the tub to meet code and to be safe. However, at the big chain home improvement stores you can buy these really cute outdoor rated electrical boxes with a disconnect in them really cheap (~$7.50). It’s much cheaper than any other box I could get. The disconnect also serves as a nifty power distribution block. I think it turned out pretty well for ghetto-rigging these switches into a box that wasn’t designed to hold them. You should also know that those aren’t regular household switches. Those are industrial DPST (double-pole, single throw) mechanical contactors designed to start and stop heavy-duty motors and rated for 30 amps at 220 volts (I got them on Ebay for $0.99 – for both of them). Regular household switches won’t survive switching circuits drawing this much current.
The box on the left houses the thermostat and indicator light and the switch that controls the pool light. Of course there wasn’t any calibration on the thermostat, so I’m trying to calibrate it using a thermometer in the tub. I’ve got some very approximate marks, but so far it’s mostly turn it up if it’s too cold and turn it down if it’s too hot.I do need to do something about a switch cover for the light switch. It is on my list of things to finish.
I said above that the disconnect in the switch box wasn’t really THE disconnect. All the wiring for the hot tub passes through this GFCI breaker which is mounted on a fence about 8 ft. from the tub. This breaker will disconnect all power to the tub. I ran power to this GFCI breaker from a regular breaker in the service panel for the house (a breaker that is dedicated to this circuit). I took the cover off of the GFCI breaker for this photo. I also took the opportunity to run wiring to a 110 outlet (also GFCI) so that I can plug in outdoor lights, or a boom box, or a blender full of margaritas… There’s also a 110 circuit (again GFCI protected) running to the hot tub to control the lights.
When I first fired up the hot tub I didn’t have any insulation around it. I planned insulation, just hadn’t gotten it installed. It was pretty slow to warm up and wouldn’t get real hot on a cool evening. Since then I’ve installed this reflective insulation and it works very well. This stuff is like heavy duty bubble wrap with aluminum foil on both sides. It’s stiff enough that it stays in place quite well (although a little bit of duct tape doesn’t hurt) and should be waterproof. With the insulation the tub heats up better than I had hoped. Although I installed a 4kW heater element (to keep the whole electrical load under 40A), the tub heats at about 5 deg. F per hour. That means I can keep it around 85 all day for the kids to swim in, turn on the heater at dinner time, and the wife and I can have a hot soak after the kids go to bed.
I haven’t built an insulated cover for the hot tub yet, but that’s on my list. I’m thinking about sheets of rigid styrofoam insulation and a light wood frame. Right now I’m using a vinyl solar cover designed for small above-ground pools. I don’t think it has much insulation value, but the solar effect is obvious and I’m sure it cuts down on evaporative loss. You probably also noticed in the picture of the insulation above, that there isn’t any insulation on the pipes. My plan is that when I finish the skirting around the deck I’ll use sheets of stryrofoam insulation on the inside of the skirting and the underside of the deck so the whole tub will be sitting inside an insulated box.
This is the light for the hot tub. I already had a transformer for low-voltage landscape lighting running a couple of lights in the pool area. I moved the transformer under the hot tub deck and ran the wiring through a switch (the switch on the transformer is just set to “ON”. That switch now controls the landscape lighting and this light for the pool. For a pool light I purchased a plastic housing for a pool light (only about $15.00). It’s just a plastic lens with a gasket and nut system so that it seals into a hole in the pool. The light is a low-voltage 20W landscape light aimed through the lens. It doesn’t get very warm, but it is set so that it doesn’t actually touch the housing. It works great.
So, now I have it all…A hot tub in my back yard. Warm swirling water. Bubbles and a filter. And a cute blonde in a bikini. (Two cute blondes!!) Besides all that, I built the hot tub myself (fairly cheap)!
Was it worth it? Would I do it again? How well does it really work? It works great, I would definitely do it again, and it was easily worth it. The stock tank really worked out well. The texture is very pleasant and the shape is very comfortable. It’s even a nice color. It’s big enough that it works well as a kiddy pool (and would make a great hot tub for a big party). The pumps, controls, and jets work just great. The arrangement of the jets is very comfortable. I really like soaking in the tub. It was a fun project and kept me amused for a couple of months.There are still a few minor thing to do. There are a couple of leaks in the plumbing that I’ll need to fix the first time I drain the hot tub. I still need to finish the deck and skirting (I’ll finish the deck and stain it immediately, the skirting might wait a while). 

It was a great project and turned out well. There have been some requests for specific information on the cost of the project. I’ll post some more detailed breakdowns one of these days.

Meantime,
Happy Soaking!

I hope you enjoyed this page and I hope it inspired you to build your own hot tub. Let me know if you have any questions/comments.30 May 2005
Update – December 2005We’re still using the hot tub and still having lots of fun with it. I did finish some work on it recently. I was waiting to finish the skirting and insulation until the first time I drained the hot tub because there was some plumbing I wanted to do. I finally needed to drain the tub. While it was empty I added some valves so that I could control flow to some of the jets. I wasn’t getting enough flow to make the passive air system work. Now I’ve got good bubbles through some of the jets and the ozonator works great.
I also added some more insulation. I added a layer of the mylar coated bubble wrap outside of the plumbing. I also installed a layer (two sheets thick) of styrofoam insulation under the skirting. This insulation should be enough to keep the heating bills down during the winter (I hope).
I also finished the wooden skirting. In this picture I haven’t sealed it yet, but it is installed.The cover has been a real problem. A custom cover for a hot tub this big would be really expensive. I started with a cover built from sheets of styrofoam insulation. It worked great, but the foam didn’t hold up to the elements (got chalky and crumbly). Then I made a cover from the mylar bubble wrap with a cute roller to hold it. Worked great, except the aluminum coating didn’t hold up to pool chemicals (in fact that’s why I finally had to drain the hot tub). Right now it’s just covered with a sheet of “solar” pool cover (just blue bubble wrap). It keeps the trash out and minimizes evaporation, but it isn’t enough insulation. I’m thinking now about building one using pourable urethane foam (unless someone has access to cheap sheets of 3″ thick styrofoam).
I’ve had several people ask about how much it cost to build this hot tub. I didn’t include costs when I put up this page because there are a lot of variables that affect the cost. You could save money by building a smaller tub (cheaper tank, less wood for deck, less plumbing). The stock tank was the biggest single expense. A tank big enough for two people costs less than 1/2 as much. You could save money by using one pump instead of two (maybe fewer jets, they were pretty expensive). I bought a lot of parts on Ebay. How much these things cost depends on how patient, flexible, and lucky you are. Please use my cost estimate only as a very rough guideline. You might spend more, but you might also spend much less.I spent about $1200 building this hot tub/kiddy pool. It’s been worth every penny.