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Because hot tubs come in a whole host of sizes and are each fitted with their own components, it can be a challenge to know exactly how long it takes a hot tub to heat up.
Hot tubs heat up at a rate of 6-11°F (3-6°C) per hour. The temperature of cold water averages 50°F (10°C), which means it takes between 5 and 9 hours to heat to 104°F (40°C). Standby mode reduces a hot tub’s temperature by around 20°F, meaning it takes 1.5 to 3 hours to heat up fully.
If you’re looking to buy a hot tub, it’s vitally important to take the time to understand the factors that influence heating time as budget models can be very uneconomical.
Amount of time to heat a hot tub
There are four instances when you’ll need to heat the water in your hot tub, which can be divided into two categories:
- Filling for the first time
- Adding fresh water after draining
- After winterizing during the coldest months
- After lowering the temperature using standby mode
Time to heat a hot tub with freshly filled water
The majority of hot tubs are able to raise the water temperature between 6 and 11°F (3-6°C) per hour.
Depending on the season, cold water from the faucet (tap) in the United States ranges between 45-55°F (7-13°C), giving us a year-round average of 50°F (10°C).
The recommended maximum temperature for a hot tub is 104°F (40°C). If we take the average faucet water temperature of 50°F, we see that it would take between 5 and 9 hours to heat up fully.
To the inexperienced, those figures might seem far too long, but think for a minute how long it takes to heat just one gallon of water on the stove.
Now multiply that figure by 300 (300 gallons being a typical-sized hot tub), and you can see why it takes so long. Just be thankful that you don’t have to heat a swimming pool!
Time to heat a hot tub from standby/sleep mode
Once heated, most modern hot tubs have been designed to maintain the water temperature. When you place a hot tub in standby or sleep mode, the temperature is reduced by around 20°F (11°C).
At a warm-up rate of 6 to 11°F per hour, having to raise the temperature 20°F will take anywhere from 1.5 to 3 hours.
Leaving your hot tub running all the time might seem like a huge waste of electricity, but the combination of built-in thermostats and super-insulating materials makes it far more economical so long as you’re a frequent user.
Unfortunately, cheaper hot tubs are typically more expensive to run because they’re not as thermally efficient. Because they have to work harder at heating and maintaining their temperature, it results in higher energy bills for you.
Factors that influence heating time
Now you have a general guide to hot tub heating times, I want to let you know the factors that most influence how quickly a hot tub can get to the ideal temperature, as well as what to look for to ensure the hot tub is thermally efficient enough to maintain that temperature as economically as possible.
The great thing is that you have (almost) full control over all these factors, so let’s dive in.
Heater size and efficiency
Unsurprisingly, the power output and efficiency of the heater inside your hot tub play a huge role in how long it takes to heat the water.
The power rating for heaters is measured in kilowatts. As a general rule, the higher the kilowatt rating, the quicker it’ll heat the water.
Simplifying things a little, this means a 3-kilowatt heater should heat up the water three times more quickly than a 1-kilowatt heater.
Well-designed hot tubs come equipped with heaters suited to match the water capacity, meaning that are thermally efficient.
Unfortunately, the same can’t be said for cheaper models. Oftentimes, heaters on budget models are far too small for their capacity, meaning that not only do they heat up more slowly, but they also have to work extra hard.
The use of a cover
As I learned a long time ago in school, heat rises. So if you don’t have a cover for your hot tub, then you’re throwing money down the drain.
There are two types of covers available for hot tubs:
- Floating hot tub blanket
- Custom-sized, insulated hot tub covers
Floating hot tub blanket
The cheapest option is a simple floating thermal cover that sits directly on top of the water and acts as a blanket. They can be purchased online for less than $40, and all you have to do is cut them to size.
While they’re better than nothing, they don’t do much to trap in the heat of your hot tub. However, they are worth buying if you’re going to be in and out of your hot tub every few hours during the day.
Used this way between uses, they not only keep some of the heat trapped in, but they also keep any debris and bugs from making their way into the tub.
Custom-sized, insulated hot tub covers
If you’re serious about thermal efficiency, what you really need is a fully insulated cover that’s gold-plated and diamond-encrusted. Only kidding… Gold is a terrible insulator.
Insulated hot tub covers are specially made to fit each hot tub model perfectly, which dramatically decreases heating times and allows your hot tub heater to work less hard. They also trap maximum amounts of heat when the hot tub isn’t being used.
The annoying thing is that hot tub covers aren’t cheap and have a limited lifespan of around 5 to 7 years, no matter the quality. Over time, they begin to soak up moisture which leads to deterioration and reduces thermal efficiency.
It’s important to look over your hot tub cover routinely for any cracks or holes that have appeared. Once you notice signs of wear and tear, it’s time to order a replacement.
Although hot tub covers are a little pricey, you’ll be able to recoup the money during its lifetime with lower electricity bills.
Both the quality of the insulation and the quantity used have a huge impact on how quickly a hot tub heats up and how well it maintains its temperature.
Older hot tub models are poorly insulated by today’s standards, which is something you’ll want to watch out for if you’re looking to buy a second-hand model.
Constantly leaking heat will leave you frustrated as it takes far longer to heat each time and will take a lot more energy to maintain that temperature, meaning higher electricity bills.
If you haven’t yet purchased a hot tub, it pays to spend a little more on a hot tub with thermally efficient insulation. Look for hot tub models that have full-foam insulation as a minimum.
We’ve just seen how important a cover is for efficient heating, but a great deal of heat can also leak out from tiny cracks in the hot tub cabinet.
It’s a really good idea to add insulation to the cabinets of your hot tub if it doesn’t already have it. If the cabinets do have insulation, make sure to check for any cracks where heat might be leaking from.
Yet another spot where heat escapes is in the base of your hot tub. Having your hot tub sit on concrete (or similarly hard surface) creates extra thermal insulation, which will speed up heating times.
Air temperature and hot tub location
It won’t come as much of a surprise if I tell you that the colder it is outside, the longer it will take to heat up your hot tub.
While you can’t control the weather, there are a number of simple things you can do to speed up the time it takes to warm your hot tub water.
If your hot tub is located in a windy spot in your yard, then creating a windshield is one simple way to stop unnecessary heat loss. Here are few ideas for sheltering your hot tub:
- Enclose the hot tub with a gazebo
- Install fencing around your yard
- Install a fence around the hot tub to protect from the prevailing wind direction
- Plant a row of shrubs to create a barrier
For the best protection possible, position the hot tub against the side of two or three walls in a part of the yard that receives a lot of sun.
The walls will absorb the sun’s heat and provide extra insulation to the hot tub. The other benefit of positioning the hot tub against a wall is that it will also protect from any winds.
Condition of hot tub components
The condition of your hot tub’s components contributes toward the amount of time it takes to heat the water. When all of the components inside your hot tub are in good shape, the water is able to flow freely, increasing the thermal efficiency.
You’ll already have guessed that the better the condition your heater and pump are in, the more efficient they are at heating the water.
But something you probably wouldn’t have thought is that even the condition of components such as the jets and filters all affect how long it takes to reach the ideal temperature.
The condition of your hot tub filter also plays a large role in reducing the time it takes to heat up. For maximum efficiency, you need to make sure that the filters are kept clean and clear using a filter spray cleaner and chemical soak.
Make sure to also replace your filter once it reaches the point where the filter cleaner stops working. Trying to save a few pennies by continuing to use a dirty filter will end up costing you more in electricity as your hot tub has to work harder when heating and maintaining the temperature.
Get yourself a floating thermometer
When you first get your new hot tub delivered, the only thing you want to do is get in there as soon as possible and start relaxing.
They say a watched pot never boils, and so the amount of time you have to wait can seem like a frustratingly long time.
To avoid going out into the yard every five minutes to check the temperature, get yourself this wireless floating thermometer.
It provides temperature feedback that you can monitor using an app on your phone from the comfort of your home. You won’t have to miss a minute of soaking time!