Reviving a Hot Tub: A Complete Heat Pump Installation and Upgrade

Recently, a client of mine, Chris, embarked on a journey to upgrade his 7-year-old hot tub, which had been suffering from several issues, including water damage, inadequate insulation, and internal leaks. 

While the primary goal was to install a new heat pump, the process revealed deeper challenges that required significant time and effort to fix. In this article, I’ll walk you through Chris’s step-by-step approach, highlighting his solutions and the remarkable results he achieved.

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Diagnosing the Issues

When Chris dismantled the hot tub, he discovered a series of problems that had been affecting its performance. Rainwater had seeped into the bottom skirt, causing structural damage and wood rot. Additionally, the hot tub had virtually no insulation, which led to substantial heat loss and obviously, wasted energy costs.

On closer inspection, Chris identified four internal leaks stemming from non-functional speakers that were completely destroyed. These leaks not only damaged the internal components but also contributed to the water damage in the base structure. 

These unexpected issues meant that the project was no longer just about installing a heat pump but about rebuilding key elements of the hot tub.

Repairing Internal Leaks

The first step was to take care of the internal leaks. Chris discovered that all four speakers were beyond repair and removed them entirely. Along with the speakers, he removed the sound system, wiring, bass speaker, and power supply unit.

To seal the gaps left by the removed speakers, Chris used UPVC sheeting, cutting it to the exact dimensions of the speaker holes. This method not only eliminated the leaks but also ensured the hot tub was now fully watertight.

Addressing Wood Rot

The wooden base of the hot tub had suffered extensive rot due to prolonged exposure to rainwater. Chris carefully removed all the rotten wood and treated the remaining areas with a wood hardener to restore their integrity. To fill the gaps, he applied expanding foam, sanded it down, and painted all visible external surfaces with Owatrol Clear decking paint.

To prevent future water damage, Chris installed a damp-proof course (DPC) around the bottom of the hot tub. This protective layer acts as a splash guard, preventing rainwater from soaking into the wood and extending the life of the structure.

Improving Insulation

One of the most critical upgrades Chris made was improving the hot tub’s insulation. Recognizing that poor insulation was a major contributor to heat loss, he implemented a multi-layered approach:

• Base Insulation: He started by installing 25mm Celotex boards on the inside floor, creating a solid, insulated foundation.
• Wall Insulation: Along the fiberglass walls, Chris added waterproof silver bubble insulation from top to bottom, followed by 100mm thick fiberglass wool for additional thermal protection.
• Outer Panels: To complete the insulation, he installed 25mm Celotex boards on the outer panels before reattaching the exterior covers.

These measures considerably reduced heat loss, ensuring that the hot tub retained warmth far more effectively. Chris estimated that the improved insulation reduced temperature drops by two-thirds, even in cold weather.

Installing the Heat Pump

Once the structural repairs and insulation were complete, Chris moved on to installing the new heat pump. This phase required careful planning to optimize water flow and minimize resistance.

He encountered challenges when trying to fit the flapper valve and T-pieces into the existing filter piping, as the flexible pipes were particularly stiff. To solve this, Chris ordered an additional T-piece and made precise cuts to the original setup.

The heat pump piping was installed with a deliberate design: the outlet pipe was sloped upwards, and the inlet pipe sloped downwards. This ensured that when the heat pump valves were isolated, water would drain away from the pump rather than collecting inside it. Chris used only four 90° bends to keep water flow resistance to a minimum.

Testing the Results

After priming the system and connecting the heat pump to WiFi, Chris conducted a series of tests to evaluate its performance. With an air temperature of 12°C and 90% humidity, the heat pump operated at 90% efficiency. It raised the water temperature by 3°C per hour, reaching a comfortable 37°C with ease.

In comparison, the old 2kW heater had only managed to raise the temperature by 1.5°C per hour. The new heat pump, consuming just 900W (0.9kW) at 90% efficiency, proved to be four times more efficient than the previous system.

Adjustments for Cold Weather

During a recent cold spell, with temperatures dropping to -7°C, Chris decided to temporarily shut down the heat pump to prevent damage. By isolating the valves and draining the system, he ensured the pump remained safe. Thanks to the enhanced insulation, the hot tub maintained its temperature far better than before, even in such extreme conditions.

Chris noted that while the hot tub was originally designed for tropical climates, his upgrades had successfully adapted it for colder environments.

Closing Thoughts

Despite the unexpected challenges and the time consumed by this project, Chris is thrilled with the outcome. His hot tub is now more energy-efficient, better insulated, and structurally sound. The combination of a modern heat pump and targeted repairs has transformed it into a reliable and comfortable space for relaxation.

Chris’s experience is a valuable example for anyone looking to upgrade their hot tub and highlights the importance of addressing underlying issues for long-term success.

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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