July 2006
 

This hot tub shell was sitting in a front yard, close to my house where I live, the sign said:
 

                     FREE HOT TUB, NEEDS PUMP AND HEATER.

Four young guys were looking at it, I laughed and said you need a truck for that deal, I drove off in my Sunfire knowing it was time to load this unit onto my 3/4 Ton GMC.  I let the tub sit on the truck for 2 weeks before I strapped it down and headed off to the cabin. Waited 2 weeks again and built this frame of 2x6's, 4x4 treated posts and concrete blocks.

I was at an auction, there was a C-Face motor/centrifugal pump. I plugged it in, the motor ran but there was little suction/pressure, and to be honest, I did not even know it was a pump for hot tubs,  but I paid $3.00 dollars for it.  My friends at Union Pumps tested it for me, and to my surprise, it pumps great.

My neighbors have been using a wood stove to heat their hot tub for years, it's always worked well and at one time I believe that it was close to 112 degrees.  At these temps it's really to hot to be good for you body, so they add cold water. Being heated with the wood stove is very cost effective, the only down sides are: the heat cannot be controlled, and someone needs to keep an eye on the stove, a good supply of firewood is needed, since the fire needs to burn along time to raise the water temp.

I thought it would be a great idea to heat my hot tub with propane, if the water temp goes to high, I could just turn down the burner, or off.

My first attempt was using an old BBQ, with 50' of 3/8" ID copper tubing, I have three 1" gate valves to control the flow of water.  I filled the tub with cold well water, about 48 degrees, fired up the BBQ, adjusted the valves, and waited, and waited.....   10 hours to raise the temp to about 80 degrees, and one full 20 pound tank of propane.  I used a blue solar blanket and a vinyl pool cover to retain heat for the night.

By the next morning, my temp had dropped a couple of degrees, I again fired up the BBQ with another full 20 pound tank, and I was able to raise the temperature to 102 degrees by the late evening.  My first attempt had worked, we enjoyed that warm water for about 3 hours, sipping Amaretto DiSaronno on ice, coolers for my gal, and the company of some of the neighbors.

This unfortunately was not a cost effective way to heat my tub, that's when I searched the internet to find out about heating water, what water weighs, how many Btu's required to heat a gallon of water, along with some other critical data.

My search found: Todd Harrison and The Red Neck Pool Heater, Todd has also created a BBQ heater for his 8000 gallon pool, with great success.  I used Todd's math, sent an email to him with my thoughts and plans and any secrets that he could pass my way.

My hot tub:
430 gallons x 8.35 pounds per gallon = 3590.5 pounds x 54 degrees = 193887 BTU's divided by 95475 BTU's per gallon = 2.03 gallons of propane.

I tested my water flow, I have 2.5 gallons of water at the tap, my goal was to try to have close to 3 gallons of water in the heated lines at all times.

The bottom line was:  I needed more volume/flow of water being heated, a higher heat, and a more efficient way to retain my heat. I went on a crazy hunt for 1/2" copper tubing, a yard sale yielded me seven 10' lengths (70') and a bag of 90's for a total cost of $33.00 dollars.  There was even a house being knocked down, the owner let me get the remaining copper (37') for $5.00 dollars.

Then one of our local building supply companies decided to close it's doors, a sale began.  I picked up 36' of 3/4" copper Type L, and a whack of 3/4 fittings at -45% off. My father also had 9' of 3/4" in his basement, and there was 4.5' of 3/4" at work that was never to be used. Thanks boss man.

Close to one year before all this, another neighbor was giving away 2 wood stoves, I took them, gave one away to a friend, and kept the one that I thought would make a great heater for a hot tub, should the opportunity ever arise.

Again I went to the internet to find a burner that would now suit my needs, I found the Bayou Classic High Pressure Propane Jet Burner from Cajun Outdoor Cooking , this unit can burn 185,000 Btu's.  I had it sent to me all the way from Louisiana, since my local stores here in BC could not supply that many Btu's at a reasonable cost, or even come close to the Btu's.

I removed the burner from the stand, cut a hole in the bottom of the stove, and mounted the burner in place.

It was now time to do a test burn. I mounted the temperature gauge from the BBQ onto the exhaust stack of the stove just to see what I could get.

To my surprise, on low, just a small flame burning, the temperature went to 350 degrees... I cranked the valve wide open, let it burn... This next picture shows the temperature over 600 degrees. I waited a few minutes and the temperature gauge reading was at 800 degrees.  Since that was the maximum reading I could get from this gauge, I really don't now how high it could go,  but friends are saying I now have a mini kiln.

I used a drawing program to layout the copper piping.  My idea is to criss-cross the piping in rows, starting with 3/4" and working my way down to 1/2" and finishing off with 3/8".  My theory here is, the 3/4" will fill the lines with some good volume of hot water, step it down to the 1/2", this will slow the volume down and perhaps heat the water even more, then step it down to the 3/8", again slowing the flow and heating the water even more.  Before I couple the sizes together, I will test the water flow and exit temperature of the water, just in case I don't need all the extra copper.

This is my first row the heat exchanger, and where I will leave this for now.  Once I return to the cabin, I will continue to build this, and have more pictures to share.

While also building the heat exchanger, I also have been working on the hot tub framing.  I gave this some thought, and this is what I came up with.  I want to be able to walk out my front door, have a deck level my current deck, but I also want my friends to be able to just go onto the tub deck if they decide that hot tubing is not for them. So far, this is what I have created.  I will build a railing around the top, add a step up to the tub and to the wrap around deck.  So far, it's looking pretty good...

I did some research on hot tub covers, and I was able to find Mansonville Plastics, they sell the styrofoam that is tapered from 4"-3" in a 4'x8' sheet.  I bought 2 sheets for under $70.00 total.  I will use this thick white poly (seen in picture) to wrap the styrofoam to create my own cover.

While soldering my copper, I ran into a small problem, my propane torch was freezing up on me, and I was not getting the required heat to do a good job.  I picked up a new bottle and torch head, and over the weekend I completed my second row on the heat exchanger.

Reading earlier from Todd Harrison's web site, I knew it was time to pressure test my joints,  so I filled a plastic tote with water, plugged both ends, and attached the air hose.  Three leaks, glad I checked this now, as later with more rows it would be very hard to fix.  Two more rows to go with the 3/4", and at that time I will test the flow and temperature rise.

November 2006
 

It's snowing now, and as much as i would like to be in the tub, my burner is still not complete.  Another concern of mine is the freezing.  I drain the tub after each weekend,  but I am worried that in the winter months the remaining water in the system will freeze and crack the pipes.  At this time, I will just use the hot tub in the summer months until I devise a method to totally drain the water.

Better success on soldering the joints this time, zero leaks! 

It's starting to take shape.  I have four rows complete, the fifth row is cut and just needing some 90's.  I also have five more 12' lengths of 3/4" copper pipe.  The five rows of copper is a total of 49.5 feet.  If I use all the 3/4" pipe, the burner could be a total of ten or eleven rows.  I'm really wanting to see what temperature rise I get out of "what I have" so far, just in case I don't need to use all my copper

The weekend was a short one, time only allowed me to get two more rows cut, soldered and pressure tested.  I now have seven rows assembled, and it's getting heavy!.  I did a measurement, and it looks like I can only get two more rows, since the opening on the stove door has minimums that I need to be within.  My math also tells me that I will have very close to 100' of 3/4" copper, every 40' of 3/4" copper holds 1 gallon, I should have 2.5 gallons of water flowing, heating, and rocking the system.

I finished my last two rows of copper piping, what a relief to get this task completed.  I was finally ready to drop the heat exchanger into the stove, now remember, I wanted to slide it through the stove door. This was not going to happen...  I ran into my first design flaw, some parts of the heat exchanger were larger than the opening... I removed a row of copper which I thought would fix my problem, but again, the heat exchanger would not fit into the stove.

I was now faced with a major problem, how do I get this heat exchanger into the stove???   I looked over the stove and I noticed that the top piece was spot welded together.  Out came the 1/8" double ended bits,  I pre drilled the spot welds, and followed up with a 5/16" drill bit.  The whole top of the stove was now able to be removed.

I then dropped the heat exchanger into the stove from above, as you can see, it's a great fit.

Replacing the stove top is now going to be simple.  I will use 5/16's bolts and nuts to keep it in place.  My design flaw turned out to be not a flaw in the end, as I now think this is a better way for me to work on the heat exchanger in the future.

My next step is to make a metal rack that will hold up the heat exchanger.  I currently have it blocked in place to get an idea of the required height.  I still need to drill an outlet hole, and solder 3/4" hose fitting before I can test heat exchanger.
May 2007
 

I purchased a metal bender from Princes Auto, and picked up some .125" x 1.5" flat bar cold rolled steel at Fasteel, measured twice and bent once.  A perfect cradle for the heat exchanger to sit on. Laid out the exit hole, drilled and ground the edges.

The heat exchange sat firmly in place with both inlet and outlet pipes lined up.

This view shows the head space from the burner to the heat exchanger, about 10".

I attached my hose end fittings...

Attached the stove cover with 1/4" x 1 bolts...

Dropped the top metal skirt in place, this cover sits loose on the stove...

Now for the fun stuff, it's time to run some tests.  I first hooked up my cold water tap.  I have the water entering from the top of the burner, then exiting from the bottom, my plan again here is to have the hottest water entering the tub.  I blocked the exit pipe, and checked for water leaks, all was good.

My first test is to run cold water into a 5 gallon pail, then get the temperature reading.  It's 48 degrees straight from the tap.  My water flow is about 2.5 GPM.  I adjusted the water flow to down to about 1 GPM.

7:12 pm, I fired up the burner, and turned the valve 1/2 a turn.  Remember, I am only continuing to fill the 5 gallon pail of water, not recycling the 5 gallons of water.

7:15 pm  52 degrees.

7:17 pm  60 degrees.

7:20 pm  76 degrees.

7:25 pm  87 degrees.

7:30 pm  89 degrees.

7:35 pm  92 degrees.

7:40 pm  94  degrees.

7:41 pm I turned the gas valve to be one full turn "open"

7:45 pm  99 degrees.

7:50 pm  108 degrees.

5 minutes later, my temperature reading was off the dial, +120 degrees.
38 minutes total test time.
 

2nd Test

8:24 pm, Filled the 5 gallon pail with cold tape water, let it run a couple of minutes.  I fired up the burner again, and turned the valve 1/2 a turn.  Remember, I am only continuing to fill the 5 gallon pail of water, not recycling the 5 gallons of water. *47 degrees cold water.

8:30 pm  61 degrees.

8:35 pm  66 degrees.

8:40 pm  67 degrees.
*Again, I turned the gas valve to one complete turn.

8:45 pm  76 degrees.

8:50 pm  82 degrees.

8:55 pm  84 degrees.
*Now the gas valve set at 1.5 turns open.

9:00 pm  87  degrees.

9:05 pm  93  degrees. 
*I turned down the gas valve to be 1 full turn.

9:10 pm  90 degrees.
Temperature went down, so I adjusted the water flow down to 1 GPM.

9:15 pm  94 degrees.

9:20 pm  111  degrees.

5 minutes later, my temperature reading again was off the dial, +120 degrees.

56 minutes total test time.

 

My next test, to fill the hot tub, and recycle the water, and see how long it takes to heat to 102 degrees.

 
June 2007

Saturday morning, I started filling the hot tub at 11:30 am, tub was full by 1:30 pm.

Water temperature was 52 degrees, the blue solar bubble cover was on top of the water, plus the hot tub cover was in place.   Outside temp was close to 100 degrees.

4:30 pm, 3 hours later, the water had risen to 63 degrees.

5:30 pm, water was at 66 degrees.

6:00 pm, water was at 67 degrees.   I fired up the burner, 1/2 turn on the gas valve, solar cover and hot tub cover on.  **I had the water flowing only through the heat exchanger, as I have gate valves to control the flows.  Water is flowing close to 40 GPM.

6:30 pm, water was at 70 degrees.  I turned down my water flow on the "exit" valve, trying to keep the water in the heat exchanger longer.

6:45 pm  73 degrees.

7:00 pm  75 degrees.

7:19 pm  77 degrees.

7:30 pm  79 degrees.  Lots of condensation, as you can see below.

8:00 pm  84 degrees.   Rise of 17 degrees in 2 hours.

8:15 pm  86 degrees.

8:30 pm  88 degrees.  Rise of 21 degrees in 2.5 hours.

8:45 pm  90 degrees.

9:00 pm  92 degrees.

9:15 pm  94 degrees.   Rise of 27 degrees.

9:30 pm  96 degrees.

9:45 pm  98 degrees.

10:00 pm  100 degrees.  Total rise of 33 degrees in 4 hours.

10:16 pm  Time to jump in the tub, 102 degrees.

11:00 pm, water temp is still at 102 degrees, I turned of the heat exchanger.

11:40 pm  Water still at 100 degrees, and were done hot tub'n for the night.

I covered the tub with the solar blanket and the hot tub cover.

The next morning, the water temperature was still at 98 degrees, and later that evening, 7:30 pm, the the tub had risen to 100 degrees without the need to fire up the burner.

Overall, this test was a success.


JULY 2007

Second Test, I call this one "The Hot Fill"

I hooked up the water to the burner, turned on the water and adjusted the flow to about 1 GPM, and fired up the burner, turned the valve 1/2 turn.

4:56 pm   Water out of the tap, 48 degrees, running through the burner, and entering the hot tub, 96 degrees.

8:00 pm  I increased my water flow, just a little, and turned the gas valve to one full turn.

9:30 pm  Tub is full, water temperature is 100 degrees.  I disconnected the water from the cold water tap, and hooked it up to the system to start recycling the water.

10:00 pm  Water temperature is 102 degrees.

*Added 1/4 pint of Purox to the system, all reading for chemicals read "Ideal".

Time to jump in and enjoy!

 

I would like to thank Todd Harrison of The Red Neck Pool Heater  once again for all his advise.   It's people like Todd that makes projects like this come to life!

 
 

So, now what can we build?