How to Heat a Hot Tub Fast

Let me tell you how to heat a hot tub fast as we’ve been asked this same question a few times recently.

And the best of it is, there is a very simple answer.

Coleman SaluSpa 6 Person Inflatable Outdoor Spa, Filters, Chlorine Starter Kit OK. Like us, you’ve got your hot tub, all excited and eager to give it a try.

You’ve set it up right, switched on the power —– then what do you do while you wait for ages as it heats up at a snail’s pace?

Tedious, isn’t it, the waiting?


Nothing worse after suddenly getting the urge for a hot soak and realizing it’s too cold, even if you’ve gone down the usually recommended route of having your hot tub serviced regularly, use a tight-fitting newish cover for better insulation and made sure your filters and jets are clean and working properly, as well as shielding your hot tub from bad weather…


Most hot tub heaters raise the temperature by a mere 2 or 3 degrees F per hour, depending on the size of your spa, surroundings and weather, so it can be a full day or more before it is up to where you want it.




Yes, you read that right!


You need to boost your hot tub temperature and the only way to do that is by putting in more energy very quickly – so that simply means using a larger heater.

Solar and heat pumps (shown lower down the page) barely boost the temperature in any meaningful fashion – unless you live in a desert, but then you’d be wanting to cool it down, wouldn’t you?


Pool Heaters…

For your info, swimming pool temperature can be limited in certain states owing to their laws, but as we’re looking at heating a hot tub and not a swimming pool, these laws can be sort-of ignored.

Pool heaters usually have a maximum thermostat reading of around 90 F, but this is generally to protect pool liners and swimmers from overheating through exercise, but as we are wanting 104 F or more, then the temperature can be raised easily using the thermostat.

Trouble is – some have a thermostat built-in, which may be awkward to adjust, but a quick call to the manufacturer would easily remedy that little problem.

Others have a thermostat set in the pool itself, so all that is needed is the heater’s thermostat sitting in a cooler water container until the right temperature is achieved in your hot tub, then switch it off to allow the hot tub’s heater unit to continue keeping the temperature at the right level for you.

Alternatively – why not boost the temperature to maximum ‘pool’ heat and allow your Hot Tub’s own heater to take over from there?


Propane Pool Heaters


Using simple plug-in 110volt power to drive the pump in a pool heater means while it is in use, costs are minimal electric-wise, with Propane providing the heating, giving hot water in a few hours or less.

Different sized ones provide different heat outputs, from 100,000 BTU’s (30KW) upwards and generally any Pool Heater under 150.000BTU’s (near enough 45KW) is ample to raise the temperature of a 350/400-gallon hot tub within a few hours starting from scratch.

We’ve included a few of the larger ones for you, just in case your hot tub is on the larger size.

They are easy to set up and can last for years as normal, low-powered electric hot tub heaters can take over when the water’s up to the pool temperature.


Doing it like this, you can be up and running in no time, regardless of where you live.


There are fully electric pool heaters available which means you don’t need to be messing around with gas, but they need a decent power feed to make them run properly which may add further to the cost.



So, here are our recommended suggestions for PROPANE POOL HEATERS:


Pentair MasterTemp Propane Gas Heater (125,000 BTU)

Pentair MasterTemp Propane Gas Heater (125,000 BTU)

The one we personally recommend and use ourselves is the Pentair as it is a great brand, well known in the pool heating community for reliability, ease of spares and good economy.

At 80lbs and 21 x 23 x 28.2 inches, this pool heater is not going to stand out like a sore thumb and can be easily shifted away for storage when not in use.

As standard, it comes with a plug-in 110v power cord and as the power is only needed for the pump, it is very efficient in use. It is also capable of 220-volt usage if you have it to hand.

Gas-wise, this Pentair runs on propane giving a maximum of 125,000 Btu’s (36KW) meaning under a couple of hours from freezing to near hot tub temperatures for 350 gallons is easily achievable.

There are many other larger Pentair Propane Pool Heater sizes available using the same body but with different heat outputs.

The digital display is programmable, but more than likely with a hot tub rather than a swimming pool, it will be switched on with the temperature control set and left until your water is hot enough.

On top of this, the casing is corrosion and UV-resistant and the plumbing, at 1.5 inches allows a very quick water turnover, so this may need adaptors for your hot tub unless you add extensions and just hang them over the side of your hot tub as we do.

Priming the pump can be a bit awkward, but we use a separate pump in the water line to the Pentair, to get the flow going, and once it’s in action it works great without the added pump being switched on.

Another benefit is the supplied 50-foot gas hose is plenty long enough to have the gas bottle out of sight.

In fact, Pentair also produce and sell an inexpensive conversion kit for this model so your propane heater can run on natural gas with near enough the same power output.

Check out the natural gas conversion kit out here…


For more info on the Propane PENTAIR MasterTemp, check it out here


Raypak Digital Pool and Spa Heater -156,000Btu – Propane


Raypak Digital Swimming Pool and Spa Heater - 156,000 BTU - Propane


Looking like a large desktop computer, this 115lb Raypak 156,000 Btu (45.7KW) propane gas heater is designed for easy installation on above ground pools, smaller in-ground pools, and larger spas.

Its size is  27.5 x 12 x 27 inches and it uses 2-inch piping with corrosion-resistant internals to provide a good flow.

A simple plug and play system uses 110/120 volts as standard, but a 220 option is available.

Gas-wise, the usual 1/2″ NPT fitting is fitted, so it is easy to connect up to your Propane feed.

Apparently, this model is remote-compatible, but whether that matters to you is up to you – means nothing to us as we don’t vary the temperature or timing in our hot tub using our Pentair.

Have to admit, the reviews don’t come anywhere near as good as the Pentair MasterTemp above, plus it may be a little too large for most hot tubs.

They do, however, provide a smaller version with 105,000Btu’s and better reviews, that runs on natural gas.

There are many others of much larger size, but as we feel they are a bit over the top, we have not included them here.

For more info on the Raypak Propane Heater, check it out here.



Natural Gas Pool Heaters


The smallest Pentair Natural Gas Pool Heater that fits our sizing is their 125,000 BTU’s (36KW) heater named Pentair 461059 Master Temp.


Very similar to the propane version mentioned above, but this one has a poorer customer review rating which a bit of a downer.

Obviously, there will be many happy customers who don’t even bother to leave reviews on any Amazon products – ourselves included sometimes – so check it out and see what you think.


There are two Raypak Natural Gas Pool Heaters available that fit our category, although there are many others that are just a little bit over the top for what we want.

If you need to check those out, they can all be found here.


But back to others that suit our needs.

Raypak 105,000 BTU Swimming Pool and Spa Heater - Natural Gas The first, at 105.000BTU’s is a RayPak Swimming Pool and Spa Heater – Natural Gas.

Looks very similar to the propane version above, but this one has an analogue control for heating.

Sadly, there is no pump incorporated in this unit, so you will need a pump with a minimum flow rate of 1200 gals/hour – any less than that and this unit does not work – safety cut-outs with over-heating, I believe.

It is, in fact, just a 30KW water-heating unit, so not a lot can go wrong, can it?

It acts like a big saucepan with a flame underneath and needs a constant flow passing through it, so it is nothing too difficult to understand.

Size-wise, this Raypak Natural Gas Heater measures 27.5″ x 12″ wide x 24″ deep with the gas fitting being the usual 1/2 inch NPT and the 120V power supply can easily be converted to 220V.


To read more and see the reviews, click this green tab.



Raypak Digital Swimming Pool and Spa Heater – 156,000 BTU – Natural Gas

Raypak Digital Swimming Pool and Spa Heater - 156,000 BTU - Natural Gas The second Raypak model is just a little bigger at 156,000 BTU’s, almost half as big again (45.7KW).

Now, this water heater is meant for swimming pools and spas, so the heating side of it is no problem regarding temperature achievement – In our view, it might be a bit over the top for most spas.

Being digitally controlled may be a bonus for some, but it is easy to set up.

Size-wise, it’s 32 x 30 x 16 inches makes it a bit heavier than the last one at 101lbs, but the customer rating appears to be a bit on the poor side, although the poorer reviews were from a few years ago but the latest is from a happy chappy.


See more of it here – click this green tab



Electric Pool Heaters


Moving onto Electric Pool Heaters used for smaller swimming pools which could possibly be very suitable for boosting your hot tub temperature, they range from 3KW to 5.5KW, then onto 11W.

The 3KW versions can be used directly from your household power providing you have a 220V supply, but they add very little boosting ability.

In fact, being readily available and much less expensive than manufacturers servicing and parts expenses, they could well be used as a replacement when your heating unit fails.

Admittedly, most are imported heating units, but because of this they make a big reduction in costs.

Firstly, there’s the TOPCHANCES Electric Swimming Pool and Spa Heaters, available at Amazon, one of their best sellers with plenty of good reviews.

They provide as 2KW, 3KW and 5.5KW versions and all heaters of this style are simply heating units and require a separate pump to provide the water flow.

Despite this, there are many other suppliers of similar heating units going by the name of:





Moving to the higher-powered Electric Pool Heater units meant for use with larger pools – meaning capable of boost heating your hot tub from chilled to 104F  in a few hours, one name stands out above the rest.

And this comes from HAYWARD ELECTRIC POOL HEATERS who offer many different sizes of heaters, all requiring a larger power supply than a conventional home output. In fact, they also offer gas-powered heaters too.


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