I have had an Intex 77in PureSpa Portable Spa for 5 years. When the heater/pump is turned on, the water temperature rises about 2 degrees (F) or so every hour, so approximately 24 hours to reach the maximum temperature of 104 degrees (F). Way too slow. I am considering replacing the heater/pump with a better performing one.

How to go about it ? I am a bit confused on what hardware to get and how to determine the performance of an heater/pump. Any help would be appreciated.


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    See that dainty cord there? It's small because you conveniently plug it into a wall on a 15 or 20 amp circuit. Most hard-wired spas have dedicated 30 or 50 amp circuits. You're limited by that fact. Maybe you can find a standalone pump that you run from a second circuit and throw the hoses over the side during warmup. – isherwood Jul 15 '20 at 14:17
  • As a comment only, not a full-on suggestion (I'd let the electrician chime in on safety/feasibility before taking action on this): If you can purchase a 2nd heat pump unit, you could set it to the side of the tub and either A) run the output from the built-in pump to the input of the add-on, or B) have the add-on pull from the tub and pump back into the tub (weigh down the 2 hoses, place them on opposite sides of the tub so you're not creating a hot spot). Plug the new heater into a different circuit to avoid overloads. – FreeMan Jul 15 '20 at 14:33
  • Looks like a great idea @FreeMan. I have a dedicated AC outlet not too far I could plug the second heat pump. Should be a 20Amp one. – Lou Jul 15 '20 at 15:01
  • @Lou I will repeat: Do not do this without some additional confirmation that it's safe!! I'm not an electrician, nor am I a pool/spa expert. Treat me as a random goober on the internet and qualify my suggestion with that thought in mind. While I personally don't see an issue with it, that does not mean that it's not fraught with potential dangers. – FreeMan Jul 15 '20 at 15:38
  • The problem I see with a separate pump/ heater is the controls. on the ones I saw online there was a control panel separate from the pump unit , small units like this would not be able to handle the doubling of the ampacity wiring everything in parallel. We have standards like 14 awg wire but mfg’s can use smaller wires in listed assemblies because their use is limited to the system as delivered. Just doubling the heater could melt down the wire harness if it worked it probably would not cycle many times before the contacts melted down if relay and may blow fairly quickly if solid state. – Ed Beal Jul 15 '20 at 15:41

The hardest material on earth to heat

With off-grid homes, they sometimes use solar-thermal panels to collect the sun's heat. The early systems circulated the solar heated water through "tanks full of rocks" during daytime, to heat up the "rocks"... and then at night heated their house with the extra heat.

But what are the best rocks? Which material holds the most heat? Scientists did an exhaustive search, looking at every element and compound known to science. It was -- are you ready for it?

H2O. Plain water.

It holds more heat than any other substance, and that means it is also the hardest substance to heat up.

So let's crunch the numbers. Your tub holds 210 gallons. That's 1750 pounds of water. A "BTU" is the energy needed to heat 1 pound of water 1 degree F. So your tub takes 1750 BTUs to do that. (we're not talking BTU/hr, yet).

Your heater is 1300 watts. 1 watt is 3.41 BTU/hour. 1300 watts is 4433 BTUs per hour.

Applying that to 1750 pounds of water should raise the water 2.533 degrees F per hour (4433/1750). In theory.

You say it's doing about that. So the heater is working pretty efficiently.

Plain power sockets are painfully limited

Why is it only 1300 watts? Because the heater has a common plug-in cord that plugs into any ordinary wall socket. (Mind you, the circuit feeding all the wall sockets on it, has a capacity of only 1800 watts to begin with). In order for an appliance to be certified as safe, a common cord cannot draw more than 1500 watts. It needs some for the pump, so that leave 1300 watts. Ouch.

So 120V is a real pain in the keister.

Now, you had an idea to use a dedicated 20A, 120V socket. Again we must derate 20% so we are at 16A @ 120V, or 1920W. OK, that's 6547 BTU, or 3.7 degrees per hour warmup. Added to your 2.5, that's 6 degrees per hour warmup.


Now, the way I'd do that is, they make "tanked" 4 gallon water heaters that take 120V @ 16A. Gosh, there'll be 4 gallons left in the heater, who cares out of 210? So I'd just plumb that "tanked" water heater to the loop going from the regular heater to the hot tub. You'll want those lines to be insulated, so get some snap-around foam pipe insulation.

Mind you, this heater needs to be hardwired, and it should be on a GFCI for your family's safety. Anytime you're doing some sort of horky-dorky "hack" like this, you should always GFCI-protect everything - and that goes triple for anything involving water! I would install a switch-rated GFCI "deadfront" in the receptacle location, and use that to turn the heater on and off. (it has an "OFF" label for "test" and an "ON" label for "Reset").

Now you're playing with power

The 120V is also a limitation... big heaters use 240V. Let's take a water heater, 30A @ 240V. It's only allowed to use 80% of circuit capacity, or 24A, and builders realistically aim for 23A @ 240V. Let's see what that does for us. 23A x 240V is 5520 watts.

Let's plug that in. 5520 watts is 18,800 BTUS/hour. That's 10.75 degrees per hour. That's a little bit better.

Let's take a modern "on-demand" heater with dual 40A circuits - again runs a bit shy of 80% of that, so 31A x 2 = 14,880 watts. That's 50,740 BTUs/hour. So into our 1750 pound tank, that's 29 degrees per hour gain. That's more like it!

If you want the bigger kick of a 23A heater, do exactly the same above thing, but with a 15-20 gallon water heater that is 5500 watts. The GFCI will need to be a breaker and be in the breaker panel. Which means you will need a disconnect switch. This is a statutory Code requirement, but you actually will want it! Because you need to be able to turn off the booster heater when it's at the right temp (or if the main pump is turned off)! So get a really decent disconnect with a knife switch made to throw everyday, not one of those hokey pull-outs.

If you want the super big kick of an on-demand heater, you'll probably need to upgrade your electric service also. That would be insane; you'd be at temperature in 2 hours.

2 hours, right? Water is really, really hard to heat.

  • FYI - I really appreciate your answers. Not only are they full of all the technical details, but they're written in a way that the average Joe, who hasn't spent a lifetime studying electricity, can actually understand. The story telling is excellent and the little snarky comments that get thrown in golf clap make them human. If this electrician/construction worker/Home Improvement question answerer gig doesn't work out for you, get to writing the Great American Novel™! – FreeMan Jul 16 '20 at 12:58
  • Nice ! Thanks a lot for all those explanations. I understand better now. Yeah, it doesn't seem like an easy project ... – Lou Jul 16 '20 at 15:18
  • Harper, what do you think of the "EcoSmart ECO 11 Electric Tankless Water Heater", 13KW at 240 Volts ? Going for $200 on Amazon (amazon.com/dp/B001LZRF9M). They say it's pretty fast (heat up 2 gallons per minute). – Lou Jul 17 '20 at 23:33
  • @Lou It's a beast, but if you've got enough electrical service to power it, that will work. Make sure there's always water in it when it's running. You know it'll cost more than $200 to install... – Harper - Reinstate Monica Jul 18 '20 at 3:15
  • Nice @Harper-ReinstateMonica ! Thanks for the help. I will ask my friend who is a certified electrician to install it for me actually. He should give me a good price. Maybe $500 total for everything. Better than buying a new jacuzzi for $2,000 ! lol – Lou Jul 19 '20 at 15:47

The part is a heating element that creates the heat. portable spas are limited on the amperage So just changing out the element is probably not feasible without a fair amount of work. Looking online it states the heater is 1300w that’s the only specifications I could find the cord looks like a standard cord in the photo the element you have draws 10.3 amps even on a 20 amp circuit that leaves 6 amps for the pump , that’s not much. The controls probably are not designed to handle much more and if they could you would start tripping the breaker. Safety would be the main concern here I looked on line and did not see a conversion to a higher power heater and pump (that would require a larger circuit) so in this case I would not try to increase the element wattage as that may cause electrical failures, possibly melting parts due to the higher heat and from the higher current draw.

  • Thanks for the answer. I see what you mean. I have a dedicated AC outlet not too far I could use. Still 20 Amp. But only the heat pump would be plugged on it. How does it sound ? Maybe I could get a heat pump drawing 18 Amp ? Would that help in performance ? If not, I am willing to get an electrician wiring an higher Amperage. – Lou Jul 15 '20 at 14:56
  • Code limits that 20 amp circuit to 16 amps for safety and this allows your pump to start, when pumps start they draw 3-5x normal current the manufacturers know these limits and would not make something that violates the rules (would not be able to get UL or other listings needed to sell the products). Do you have separate plugs for the control and the motor/ heating element? This would be unusual I have worked on very few prices of equipment other than transfer switches that are fed from more than 1 supply. – Ed Beal Jul 15 '20 at 15:36
  • No, it's the same plug. But I would think a new plug would be needed to finalize all of this. – Lou Jul 16 '20 at 14:25
  • Lou have you read or do you not understand that your controller could not push 2 units. Even a separate water heater needs flow and the OEM limit the temp to 104 if you use a water heater and the temp hits 140 are you going to start melting the plastics in your blow up spa? Go for it at least they are quite cheap to replace. – Ed Beal Jul 16 '20 at 15:12
  • No need to be rude. Check your attitude. If I have to install a second plug, I can do it. That's not a problem. I can also install a temp control on the separate water heater. – Lou Jul 17 '20 at 23:05

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