Portable Water Heater for a Hot Tub or Pool

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Introduction: Portable Water Heater for a Hot Tub or Pool

I recently purchased a portable hot tub - Intex PureSpa 6-Person Portable Inflatable Bubble Jet Ho t Tub. While looking at the specs and reviews I was concerned about the heating capacity of the unit. The 1,300 Watt heating unit only heats the water 1-2 degrees Fahrenheit an hour. Customer reviews also indicated they had a significant increase in their electrical bill. This information lead me to come up with a portable water heater solution. I am not a handyman by any means so suggestions and optimization ideas are very welcome. Please let me know what you think for my first Instructable.

Step 1: Pieces and Parts

Here are the basic pieces that I used to make the portable hot water heater.

Camplux 5L 1.32 GPM Outdoor Portable Propane Tankless Water Heater

Flojet 03526-144A Triplex Diaphragm Automatic W ater System Pump, 2.9 GPM 50 PSI, 12 volt DC

4 - 1/2 to 1 1/4 " stainless steel hose clamps

2 - 1/2" galvanized coupling

2 - 1/2" Male NPT X 1/2" Hose Barb

2 - 10' braided vinyl tubing 1/2" inner diameter

Kastar AC Adapter, Power Supply 12V 6A 72W

Teflon Tape

Wrench and Screw Driver

Step 2: Making the Water Connections

Apply Teflon tape to the threading and hand tighten the 1/2" coupling and 1/2" to hose barb to the water inlet and outlet on the water heater unit. Affix the hose to both of the hose barbs and tighten with the hose clamps.

Step 3: Connect Hosing to the Pump

Using the hose barb connections supplied with the pump attach the hoses and tighten with hose clamps. Ensure you follow the directional arrow that indicates the flow of water through the pump so it draws water from the water source and into the water heater.

Step 4: Connect the Propane and Check for Leaks

Connect the supplied propane supply line to a 20 lb propane tank and check for leaks by using soapy water on connection points. If you see bubbles turn off the propane and tighten that connection point, do not overtighten. Once no leaks are detected mount it in a safe location. It must be mounted outside where adequate ventilation is provided. I had plenty of space under my deck where the heat could dissipate and not overheat the wood.

Step 5: Attach the Power Supply to the Pump

Attach the power supply to the water pump. The outside of the barrel is negative (-) and the inside is positive (+). Do not plug the pump in until all water connections are attached and the suction end is submerged in the water.

Step 6: Check All Connections and Turn It On!

Check all connection points to ensure they are adequately tight and not leaking. Ensure propane is turned on. If not already installed place the 2 D cell batteries in the water heater. Ensure both ends of the hose are underwater. The suction hose must remain submerged at all times.

When you are ready to connect the pump power supply and water will begin to flow. Once water flow is detected in the water heater it will auto start the flame. You can view this in the flame window on the front of the water heater unit.

Relax in whatever you are heating and watch the temperature rise. Be careful, if you have the water flow turned low and the gas high it is capable of producing hot enough water to scold and burn. This should be supervised at all times by a qualified adult.

Enjoy! :-)

Step 7: Follow Up / Updates

Thank you to everyone who built or provided suggestions for this project.

Something that appears to be a reoccurring problem is the pump overheats. Quite a few commenters suggested using a hot water based pump. I am curious to replace that original pump with one designed for hot water. I am not sure if it will have the same water pressure as the original pump above. I am suggesting this pump as a replacement 3 GPM hot water pump

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2 People Made This Project!

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70 Comments

0
GBX23
GBX23

Question 8 weeks ago

Won't the chlorine or bromine in the spa water cause corrosion inside the heater? My spa has a salt water chlorine generator. Won't the salt also cause corrosion inside the heater? Won't the salt also cause the pump to eventually seize up? There are other chemicals in the spa water not found in tap water. I use dry acid (sodium bisulfate) to lower the pH. I use boric acid as a pH buffer and to make the water "sparkle." I use potassium monopersulfate to "shock" the spa after use. I use "Silk Balance" to prevent biofilm growth inside the passages. Nobody knows what's in that stuff except for the people who make it. Seems like a whole bunch of unknown chemical reactions might occur on the hot metal surface of the heat exchanger. Not to mention the sweat, dead skin cells, hair, body lotions, dust and whatever else you can think of that's going to be sent that way. Of course, the built-in electric heater has to deal with all that stuff as well, but I would imagine that its hottest surface doesn't get anywhere near as hot as the heat exchanger in the gas heater. It also has a filter to keep out the hair, skin, etc.

0
Ben28472
Ben28472

8 months ago

How long did this take to heat the hot tub from cold (let’s say 60degrees)?

0
weber713
weber713

Reply 3 months ago

We never attempted that. We run the normal heater to keep it at q decent temperature and use this set up to quickly heat it for use. Sorry

0
Wez
Wez

3 months ago

PUMP:
Has anyone tried using a spa circulation pump with the propane heater? Vevor makes a 1/3hp pump which will push water over 20gal a minute (ball park figure). I assume (currently pending vevor support to answer) I can cut the wattage to reduce this down to 10gal a minute which the tankless I’m getting will reduce further to 4.5gpm without damaging the pump. I want to go heavy duty and reduce to about this level so no fluctuations occur in the water supply that will negatively impact the heater. Added benefit - it has a filter built in for pools / spa and is made to handle heat to 120degrees (perfect cause I’d want it to break before burning me at 140 degrees).
If you are doing a 12v pump setup you should get an accumulator tank. This will ensure a very consistent flow… actually this might be good for any setup.



HEATER:
I am getting the vevor 18l/~4.5 gpm tankless propane heater. People claim in reviews they have used it for over two continuous hours with no shut off at 20 minutes. The 20 minute shut off issue doesn’t make much sense to me either some of these are full house water heaters… when it shuts off does the water stop flowing or does it keep flowing but the flame shuts off? Is it because of constant use or is it because of temperature?


SAFETY:
You can install a temperature controlled switch to shut the heater’s pump off when it reaches X temp. These are commonly used in home brewing setups where you need a constant temp for fermenting. I haven’t done my spa project yet - but I have used these in home brew setups. I think the hardest part of this would be installing it so it looks good/pro. Nothing worse than a diy looking like a diy.
Worst case - I’d install a timer on the pump. You don’t want someone falling asleep and boiling to death.

0
Wez
Wez

Reply 3 months ago

My pump choice turned out to be a dead end. I’ll be using the sea flow pump that most others use. For those with the 20 minute shutoff issue - camplux stated it’s a temperature issue or otherwise as they don’t have a 20 minute timer. Make sure your regulator is working well and you have good propane flow. Don’t adjust the water beyond what it can handle for temperature. Worst case - dial it down closer to 104 and see if it still shuts off. Of course this will increase heat time.

0
cooltoolsati2fun
cooltoolsati2fun

4 months ago on Step 1

I think we're all going about doing this (keeping optimum heat of hot tub all wrong. #1. The 1100 to 1200 watts is total power used by these blow-up hot tub units. Divide that up & the heater element is weaker than little over half KW total in a simple H2O heat exchanger!

Most of all though the problem is too fast of cooling w/ air bubblers/jets on;
Solution? Either add a heat element to heat the air or better yet box the unit in so you don't have COLD/cooler air feeding the air pump passively off the hot water circulating/heating air in to jets!

Too obvious for the Geniuses who design these Hot Tubs to worry about making them more efficient. But.... for us, if they really wanted to sell them, they'd make them more efficient in the 1st place.

Generally speaking, there are ways most expensive units do that can help all these HOT TUB heating problems.
1. Use the Heat from the enclosed Pump Motor to exchange its heat into the water flow.
2. Instead of drawing COLD AIR from the ground, deck, floor... build housing unit to pull hot air off the top of the unit or at least maybe an air pre-heating element to Air Bubbler!
3. Insulate the whole Hot Tub better (especially where it gets AIR for Bubbler Jets!
with 2 in thick styrofoam 4ft x 8ft board!

0
jonfen32
jonfen32

Question 1 year ago

Recently completed a setup very similar to this. It works great, until we turn on the air jets on the tub. Then the pump begins to sputter and the heater won't ignite. I then have to back flush the heater to get it working again. Maybe air gets trapped in the heater? I am stumped..

0
weber713
weber713

Answer 8 months ago

We had the same issue when I first started using the system and came up with the same culprit, air. You need to position the intake somewhere that it will not take in air to keep running. We have found our perfect location after some trial and error, but for us it is very close to where the pump connects to the hot tub itself, there is a small break in the bubbles that works perfect. Hope that help you.

0
omhoekstra
omhoekstra

Question 9 months ago on Step 6

How do you keep the temperature on the right level? Is there a thermostat in the heater? I would like to replace the electrical heater in our jacuzzi with a propane gas heater but I just don't know how to keep the temperature at 38 degrees Celsius all day long. Thanks in advance for your help!

0
jonpraed
jonpraed

Question 9 months ago on Introduction

If these set ups are recirculating hot water from the hot tub into the heater, doesn't the gas heater have a temperature overheat sensor that will shut off if the water going through the heater is above a certain temperature? I'm told by one manufacturer the sensor will turn off the heater if the inbound water is over 70F. They are designed to heat cold water, not to re-heat already hot water. And if the sensor turning off isn't a problem, how do you guard against the risk of scalding? If the hot tub is 100F, and the heater is capable of a 40F or more temperature gain, the water exiting the heater could easily scald someone as it re-enters the hot tub. The heaters I've looked at claim their minimum temperature gain (with gas flame on low and water flow on high) is still 35F or more. I don't see a way to run 100+F water through the heater without it either turning off or generating scalding water, but no one's addressed this in the posts, so I must be missing something.

0
KevinW277
KevinW277

2 years ago

I have the same style setup, flow Jet pump, eco temp L5 heater, and digital timer, seems like water flow is slow, I piped it into the inputs and outputs in the spa, seemed like it worked well for a couple days, but because the flow is so little it’s like it doesn’t maintain water temp well. Last night my pump started the cycling and shuddering also. It’s almost like the heater doesn’t have enough flow to keep up with circulation.

0
0Errant
0Errant

Reply 11 months ago

How did you use the in/out on the spa? And are you still using the spa’s heater/pump/filter unit?

I’ve been wanting to upgrade the heater on my spa. It seems like there should be a way to use the propane heater in conjunction with the spa’s original pump setup, eliminating the need for a second pump, yeah?

0
KevinW277
KevinW277

Reply 11 months ago

I took the pump apart, the hose that screws into the side of the spa I put a fitting to hose adapter, I used a sur-flow electric pump with a wifi plug to be able to cycle it a few times a day for 14-20 mins each time, it turns the shower heater on when it senses the water flow, maintains 104 no problem. I also adjust how long it runs based on the outside temp.

0
weber713
weber713

Reply 1 year ago

I have been playing with settings on the heater unit and think I found a happy medium. If you drop the flow rate but keep the temperature higher it reduces the strain on the pump and keeps it running longer. One fellow commenter recommended a hot water pump not the flow jet. I will have to see if I can locate one with similar specs to add into the process above.

0
0Errant
0Errant

Question 11 months ago on Introduction

Dave, isn’t there a way to take advantage of the spa’s original pump with the propane heater? This would eliminate the need for a second pump and filter setup.

0
millingby
millingby

3 years ago

How did you bypass the 20 minute auto shut off feature of the water heater?

0
jimrock66
jimrock66

Reply 2 years ago

I used a timer 19 min on 1 min off then back on

0
mwemaxxowner
mwemaxxowner

Reply 11 months ago

The best I've seen is a timer that will do 15 on 15 off. What have you found that will do intervals of 19/1?

0
nosaints09.ns
nosaints09.ns

Reply 1 year ago

120ac to 12dc timer

0
weber713
weber713

Reply 3 years ago

Great question. I was originally worried about the auto shut off, however, it has not been an issue. I typically let the unit run for an hour and then allow the system to rest for a little while before restarting. I have not had an issue of it shutting off at the 20 minute mark.