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Can You Fill a Hot Tub with Hot Water? (No, but you can do this)

By: Author Jeff Campbell

Posted on  - Last updated:

Categories Hot Tub Operational Tips

Everyone loves a hot tub. But what if your hot tub isn’t hot enough to your liking? Or maybe you’re refilling it and want to speed up the heating? Can you fill a hot tub with hot water?

Avoid filling a hot tub with hot water. Most home water heaters are set between 120° & 140°. Hot tubs are designed for a max temp of 104° F. So adding hot water to a hot tub can damage the hot tub. Using the natural water from a garden hose is the safest way to fill a hot tub.

Additionally, tap water may be coming from a water softener, which can lead to corrosion & excess foam.

But that’s just scratching the surface of the real issue here which is how to heat your hot tub faster or maximize the temperature in it.

So we’re exploring all of that and more in this article.

Can you put boiling water in a hot tub? 

Hot tubs use a lot of electricity to heat up the water.

Sometimes it can take up to a full 24 hours for the water to heat up to the correct temperature. That wait can feel like forever, because who doesn’t want to soak in their brand new hot tub right away!

That being said, 3-8 hours is more of the typical range to heat a hot tub starting with the temperature from your garden hose.

So, can you fill a hot tub up with boiling water? The short answer is yes, you can fill up the hot tub with boiling water.

However, there are risks associated with doing this.

The biggest risk with doing this is risking damage to the hot tub shell. But. some household water can also have water softeners in them, which can invalidate hot tub warranties if soft water is added to the hot tub.

Even if your house has a water softener system on it, chances are your garden hose is not going through that system.

But for me, the biggest reason to NOT fill a hot tub with boiling water is the time it will take to fill it.

After all, depending on the size and shape of your hot tub, we’re talking anywhere from 300 gallons up to 675 gallons of water. I’m not sure how big of a pot you have and how far away your kitchen is from your hot tub. But that sounds like a lot of work to me!

Not sure how many gallons your hot tub is?

I break it down quickly and simply and show you a super-easy way to calculate your hot tub’s gallons in this recent article. Just click that link to read it on my site.

But overall, it’s much safer to fill up your water with cold water and let the hot tub heat it up over time.

Is adding hot water to a hot tub bad?

Yes, as previously stated, adding hot water to a hot tub can be bad. There is a large risk of damage to the shell of the hot tub.

Hot tubs are designed for a maximum working temperature of 104 degrees Fahrenheit.

Most water heaters that are in homes are set somewhere between 120° and 140°. This is so it is hot enough to destroy any bacteria that may be present.

So, if you put in hot water from your home into your hot tub, that means you are risking exposing your hot tub shell to temperatures up to 36 more degrees than it is designed to handle.

This can lead to the hot tub shell cracking or other damage that most likely isn’t covered by your warranty.

Additionally, a lot of household water systems include a water softening filter. Soft water in a hot tub can cause damage which may not be covered by your warranty. It can cause corrosion to the internal working parts of the hot tub.

How can I heat my hot tub faster?

This is the real question, isn’t it?

After all, most people searching this probably are looking for ways to get their hot tub hot again after refilling or are looking for ways to get it above 104°.

The latter I’m not going to get into due to the safety concerns of soaking in water that’s over 104°. Plus, for those of you still under warranty, tampering with your high-limit sensor will void your warranty.

But there are a few ways you can heat up your hot tub faster.

1. First and foremost, use your hot tub cover!

Without the hot tub cover, the exposure to the cold outside air will make it harder for your hot tub water to heat up. The cover is insulated, so it keeps the heat trapped inside to recirculate with the water.

Even on a hot sunny day like we get here in Texas, I can still heat my hot tub faster with the cover securely in place. Always put your hot tub cover on your hot tub when you aren’t using it.

2. The second way you can heat up your hot tub faster is to use your jets!

Turning your jets on improves water circulation and allows your water to be heated more evenly. It eliminates any pockets of cold water and gets all the water flowing through the system, including the heater.

Then, with the lid in place, all that heat and friction just gets put right back into the water.

3. A third way to heat up your hot tub faster is to use a more powerful heater

On most hot tubs, you can replace the heater assembly fairly easily.

Research different hot tub heaters and see which one will work best for your hot tub. A more powerful heater will cut down the time it takes to heat up.

Hot tub heater assembly power is measured in kilowatts.

On the low end, you have 4 kW, but they can range as high as 6kW, and typically the heater assembly can be purchased for under $200.

4. Add insulation 

Less expensive hot tubs are minimally, if not poorly insulated under the tub and behind the panels.

An easy and inexpensive way to increase efficiency and reduce heat loss is to add additional insulation. Traditionally hot tubs use spray-on foam to insulate under the acrylic shell and around jets. Then they may have fiberglass boards to insulate on the backside of the panels.

This waterproof thermal energy heat shield on Amazon can quickly be cut to size and attached to hot tub panels, or placed around and under the shell for a quick, inexpensive insulation upgrade.

The added bonus is it also should reduce the noise of your hot tub’s filter cycles.

5. Use a thermal blanket when heating up and when you’re not soaking

A thermal blanket just sits on the surface of the water under your cover. It adds to your cover’s ability to keep the heat in and keep the heat loss to a minimum. It’s also great if your cover isn’t in the best of shape.

The good news is these are cheap on Amazon. They can be cut to size if need be, but they also have several sizes available. CLICK HERE to see your options on Amazon.

By now, you might be ready to give up on heating, or maybe you want to know if you can use a hot tub without heat during the summer?

So if you’re curious if you can use your hot tub without heat, read this recent article where I get into the best strategies for cooling down a hot tub in summer when soaking in 104° water just doesn’t sound appealing.

After all, during summer in Texas where I live, just bumping the temperature down on the panel isn’t always enough to actually drop the temp.

Just click that link to read my solutions on my site.

Does a hot tub heat faster with jets on?

A hot tub will heat faster with all jets and water features turned on. This is because the jets cause the water to be circulated through the heater tube more frequently and eliminate any cold pockets of standing water.

Turning your jets on improves water circulation and allows your water to be heated more evenly. Make sure you have your hot tub cover on too, as this will help the hot tub water heat up quicker.

So turn on every waterfall, and every jet, pump, blower and water feature you have. This WILL cause the hot tub to heat faster.

I mentioned above that typically hot tubs take between 3 and 8 hours to heat up when you re-fill it from your garden hose. 

That’s a large time range.

So if you’re wondering why your hot tub takes so long to heat up and looking for some additional ways to speed that up, check out this recent article.

Just click that link to see it on my site.

Why does my hot tub take so long to heat up?

If a hot tub takes longer than 8 hours to reach the set temperature, the issue may be poor insulation, a lower-powered heater, or a defective thermostat or defective heater. But the water temperature from the hose can also vary between 60°-75° F.

And on that lower end, that can easily add 5 hours of additional heating time.

In fact, it can take up to 24 hours. This is due to a myriad of factors. But as I mentioned, somewhere between 3 and 8 hours is typical.

Issue 1 – Colder garden hose temperatures

To begin with, you’re most likely filling up your new hot tub with cool or cold water from your garden hose.

Garden hose temperatures can vary a lot. The main factors that affect the temperature of the water from your hose are:

  • Time of year – Texas in July often sees weather over 100°
  • Location – Minnesota in winter will take longer!
  • Is your water from a well?
  • Does it come from a storage tank?

So garden hose temps can be as low as 50° or maybe as high as 75°.

That’s a big range, and water heats between 3-6° per hour in a hot tub, depending on how powerful your heater is. So starting at 50° adds an extra 4 hours, even with the most powerful heater, compared to starting with water that is 75°.

Issue 2 – Your cover is off or not in good shape

Another reason your hot tub might be taking a while to heat up is that your cover is off.

Ensure your cover is on so that your hot tub retains heat better! To maximize its effectiveness, make sure it is on perfectly and that the flaps are folded down around the edge of the hot tub.

The cold outside air will work against your hot tubs heater, making it take longer. But a good cover also keeps the heat being generated inside. Even in July in Texas, I’m probably better off leaving my cover on to heat up my hot tub.

Also, make sure your hot tub cover is in good shape.

Issue 2 – Your jets and water features aren’t all on (or some jets are closed)

A third reason your hot tub might be taking too long to heat up is that your jets aren’t on.

Having your jets on helps improve water circulation, ensuring your hot tub water heats up quicker. Also, make sure that your jets are rotated to the on position. Closed jets or partially closed jets will slow the heating process.

Sometimes though, we have an actual mechanical problem causing our hot tub heater not to work, or not to work properly.

If you’re still having issues with your hot tub heating up, read this recent article.

I get into all the possibilities and solutions, and most of those are easy DIY fixes. Just click that link to read it on my site.

Final Thoughts

You can put boiling or hot water in your hot tub, but it isn’t recommended.

Doing so comes with some risks. The hot water can damage the internal machinery of your hot tub. It may also crack the hot tub shell.

Additionally, water from your house may be soft water, which can cause corrosion in your hot tub and void the warranty.

Overall, it’s much safer to fill up your water with cold water and let the hot tub heat it up over time. But, there are a few ways you can heat up your hot tub faster.

First, you should use your hot tub cover. It retains heat and ensures the cold outside air will not slow the heating process up.

Second, invest in a more powerful heater. Third, turning your jets on improves water circulation and allows your water to be heated more evenly.

Hot tubs can take between 3-8 hours to heat up, and this is due to a variety of factors. But the tips we’ve covered here will help you minimize how long yours takes.

As an Amazon Associate, I may earn a small commission from qualifying purchases if you click on Amazon from my site and choose to make a purchase. You can read my complete affiliate disclosure for more details.

Jeff Campbell
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