How I Reduced the Running Costs of my Hot Tub by 66%

Looking for reduced hot tub energy or running costs? With the global increase in fuel costs, most notably, electricity costs, many of us hot tub owners are looking for ways to reduce the running costs of our tubs.

Personally, I am in the same boat. My tub was always expensive to run. However, with the April 2022 price increases it became astronomically expensive to run. I needed a cheaper way of doing things.

Background

I built my hot tub 4.5 years ago now. At the time, my advisor John from the pool supply store told me that I was on the limit of the volume of water for a regular 3KW spa pack. I knew that but the alternatives at the time were custom made big electric heaters which were ridiculous in terms of the cost. Never mind the running costs.

Until the price increase in April 2022, my Hot Tub was costing £50 / $75 a week to run. I know this is expensive, but it is a luxury.

I also did not include any insulation in it when I built it so it is pretty inefficient in terms of retaining temperature too. I certainly do not recommend any of my customers do it this way now!

Fast Forward April 2022

If we fast forward to April 2022, electricity pricing has effectively doubled overnight. At £100 / $150 a week to run my hot tub running costs were getting out of hand. I needed a better way of doing things.

Enter the Air Source Heat Pump

I fitted an Air Source Heat Pump to a Plastic Shell Hot Tub

My good friend of 18 years Paul asked if I would help him fit an Air Source Heat Pump to his hot tub. Of course I said yes. It was pretty straight forward to do. You can read about this one here. You can also view the video on my YouTube Channel

What really caught my attention was the numbers that he was texting me the following day.

Firstly, he said that with his new 7KW Air Source, he was heating 2.5x faster than on his 2KW electric heater. That alone is pretty cool.

Then there were the running costs. When he was running on his electric heater, he was running at 93p ($1.16) an hour on his Smart Meter.

At the time he was texting he knew it was cheaper, but subsequently has sent me some more concrete figures.

He’s looked at the costs running on different power outputs (depending on the ambient temperature) and on the low end, it costs him 22p ($0.27) an hour to run 2/3 cheaper and on the high end 43p ($0.54) an hour to run which is over 50% cheaper.

Bottom line, Paul is running his hot tub on an air source heat pump on average at over half the cost of the electric heater. Plus, he benefits from 2.5x heat up speeds.

This is win win.

This was also why I wanted to add one to my hot tub. I needed some figures like this.

So, I have added an air source to my hot tub. If you want to learn how, you can read this article.

However, let’s look at some numbers as this post is about how much money I am saving.

Reduced Hot Tub Costs – How Much am I saving?

I’m going to split this section into three parts. Heat up costs, running costs and then regular “maintaining heat” costs, then I am going to draw a general (averaged) conclusion on the savings.

Let’s look first at the heat up costs.

Heat Up Cost Savings

Before I added the air source heat pump, I would turn my Hot Tub up from 33C to 39C (91.4F to 102.2F) on a Thursday evening. I would leave it heating up over night as it would take roughly 12 hours to heat up.

If we factor in the costs, this is roughly £0.90 ($1.11) an hour – multiplied by 12 hours which is £10.80 ($13.38) – ouch!

I know that everyone’s prices are different so turn that into KWH – that is 36KWH of electric to get up to temperature. Still an awful lot.

With my air source heat pump, I can now heat up from 33C to 39C (91.4F to 102.2F) in about 1hr 20mins at 15C (59F) ambient temperature outside. This is pulling roughly 8KWH in electric when the heat pump is in heat up mode. This is a 21KW Air Source so quite a big one.

Let’s turn this into monetary terms, that is costing me £2.50 ($3.10) to heat up the tub and it is doing it with 10 KWH of electric.

This is a saving of 72% on the heat up costs – WOW!

Reduced Hot Tub Running Costs

It is a little more difficult to calculate the running costs as was never quite sure if the electric heater was on all the time – but there are some considerable benefits. I can also calculate in the conclusion what the cost savings are.

We’ve seen the heat up time increase – I do have a 21KW air source heat pump on my tub but I have nearly 3000 litres (660 gallons) of a water to heat. As you saw above, for my friend Paul’s tub, he was using a 7KW Air Source (1200 litres) and saw the benefit.

My heat pump when running, draws around 8KWH of electricity and costs roughly £2 ($2.48) to run per hour.

However, huge benefit for a hot tub owner here is that I am seeing zero heat loss from my tub when I used it for a couple of 90-120 minute sessions – again at around the 15C (59F) ambient temperature outside. This is massive for a hot tub user.

Previously, I would be dropping from 39C to 36C (102.2F to 96.8F) in that time and then have to get out as it was too cold.

Hot Tub Maintenance (keeping it warm) Costs

I’ve found over the years that holding the hot tub at a lower temperature during the week when I don’t use it is a cheaper way of running the tub. This is compared to letting it go cold.

Previously, I used to hold it with my electric heater at 33C (91.4F) as I have explained. I have dropped that now to 31C (87.8F) as I have faster heat up speeds now so don’t need to hold it quite as high.

So what did this cost to do on the electric heater?

It is difficult to say really as I did not monitor the smart meter as I have been doing to get the costs for the air source. However, if we assume on April 2022 price increases which doubled, this was costing me £100 ($124) a week to heat in total.

Let’s subtract the heat up cost which was £10.80 ($13.38) which is 36 KWH and assume that the tub was running on full power for 3 x 1.5 hours (Friday, Saturday and Sunday usage) which is 40.5KWH. If it was then dropping down to 36C before I got out, and needing 6 hours to heat back up each time, another 54 KWH of electric.

Heat up and running costs are about 130.5 KWH. However, but that does not allow for the “keeping the hot tub hot” during the weekend. If the tub is losing 0.5C an hour, but then takes 1 hour to heat back up – that is another 36KWH per day x 3 to add to this value. This totals 238.5 KHW – Current prices are around £0.28 ($0.35) a KWH so that is £66.78 ($82.71)

This means that if my tub was costing £100 a week to run, the maintaining at 33C was costing me £33.22 ($41.15)

Wow – lots of calculations here but we have our costs that we can revist in the conclusion.

With the air source heat pump, this is a little easier as I just took some screen grabs from my Smart Meter to help with the calculations.

The week before I connected the Air Source, I took some average daily usage reading from my Smart Meter

On average over 5 days, I was using 22.94KWH of electric in my home. You can see some of the screen shorts of my meter below.

What I wanted to find out is what it is costing me to maintain the hot tub at the 31C (87.8F) I have it set to now.

So, over the same period, with the Air Source Heat Pump holding my hot tub at 31C (87.8F), I am using 35.86 KWH, so 12.92KWH a day more. At current prices of £0.28 per KWH, that is costing me £3.62 a day to hold the temperature.

Conclusion on How much I am Saving on my Hot Tub Running Costs

From April 2022 when the price rises came into place on electric here are my findings on my reduced hot tub running costs.

On 3KW Electric Heater

Initial Heat Up Costs                           £11 ($14)

Weekend Usage Costs                        £56 ($69)

Weekly Maintenance Costs                £33 ($41)

Total Weekly Costs                             £100 ($124)

On Air Source Heat Pump

Initial Heat Up Costs                           £2.50     ($3.10)         (arguably I don’t need this as this number is in the figures below but I will leave it in anyway)

Weekend Usage Costs                        £16.50     ($20.48)      (3 days @£5.50 a day average / 20KWH)

Weekly Maintenance Costs                £14.48   ($17.97)         (4 days @£3.62 a day average / 13KWH)

Total Weekly Costs                             £33.48 ($41.54)

Total Saving of 66% on my hot tub running costs!

What about the ROI?

Taking the retail cost of my Air Source Heat Pump which is £2564 ($3181) and I am saving £266 ($330) a month, I will have an ROI (return on investment) in 10 months.

Not bad at all, especially when electric prices are due to rise again in October 2022.

Can I help you with an Air Source Heat Pump?

If you would like some help with the parts and how to fit them to your own hot tub, then please do get in touch below.

Happy “66% Cheaper” Hot Tubbin’

 

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

Thanks - Andi

 

Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Today, I've helped over 1000 DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi