Hot tub heat pump: how it works & is it worth it

If you already own a hot tub, the heater is the expensive part. Not the tub, not the water — the electricity it takes to keep that water hot. A hot tub heat pump changes that, because it heats in a completely different way to the pump that came with your tub.

This is the plain explainer: what a heat pump actually is, how it works, the honest running-cost story including the bit that gets worse in winter, and whether it's worth it for the way you use your tub. No invented savings figures — we run real kit and won't guess yours.

What a hot tub heat pump actually is

Your tub's built-in heater is a resistive element. It turns electricity into heat at roughly 100% efficiency — one unit of power in, one unit of heat out. That sounds good until you realise it's the ceiling. It can never do better than one-for-one.

A heat pump — specifically an air-source heat pump — doesn't make heat. It moves it. Think of a fridge running in reverse: a fridge pulls heat out of its inside and dumps it out the back, and a heat pump pulls warmth out of the outside air and pushes it into your water. Because it's moving heat that's already there rather than generating it from scratch, one unit of electricity can shift three, four, sometimes five units of heat into the tub.

It sits beside the tub, plumbs into the same water circuit, and runs off a normal supply. The tub you already own doesn't change — this is a retrofit, not a new tub.

How much less electricity it uses

The measure is COP — coefficient of performance, or how many units of heat you get per unit of electricity. A resistive heater is COP 1. A hot tub heat pump runs around 3 to 5 in mild weather, dropping to roughly 2 to 2.5 near freezing. Across a UK year, plan for something like 2 to 3.

In practice that means it uses roughly a third to a fifth of the electricity of a resistive heater in mild weather, and around a third to a half in the cold. It also heats about twice as fast, so you're waiting less and paying for fewer hours of heating.

We won't turn that into a pound figure here, because it depends entirely on your tub, your usage, the season and your tariff. For a personalised estimate, try our savings calculator. If you want the physics side by side, our guide to how a heat pump compares to an electric heater lays it out.

The honest cons

We'd rather you knew these upfront than found them later.

• Upfront cost. A heat pump costs more than the heater already in your tub. It pays back through lower running costs over time, not on day one.
• Winter dip. The colder the air, the less warmth there is to move, so efficiency falls when it's near freezing — more on that in our hot tub winter running costs guide. It's still far better than resistive, but it isn't the summer figure.
• It takes up space. The unit sits next to the tub and needs airflow around it.
• A gentle hum. There's a soft fan and compressor sound when it runs — quieter than a conversation, but not silent.

Is it worth it?

Honestly, it depends on how much you heat over the year. Heat all winter, use the tub often, run it at temperature — the more you heat, the more a heat pump saves, and the sooner it pays back. Use it a handful of times in summer and the maths is tighter. Anyone quoting you a single fixed saving is guessing; the calculator is the honest way to see it for your own tub and tariff. And if you're weighing up tubs, our guide to the cheapest hot tub to run in the UK puts the heat pump in context.

Where it fits in the bigger system

The heat pump is the core of what we do, and it works beautifully on its own. But because it multiplies every unit of electricity you feed it, it pairs naturally with a renewable, app-automated setup: a bifacial solar panel, a battery power box and a smart switch box that decides when to draw from sun, battery or cheap off-peak mains — all managed from an app that learns how you use the tub and gets smarter over time. That's the full picture in our solar hot tub kit, and the same heat pump slots into a Lay-Z-Spa or any of the tubs we support. Lay-Z-Spa is a trademark of its owner; we are not affiliated — our kit is simply compatible with it.

Curious what it costs to run your tub today, before any of this? Our guide to hot tub running costs in the UK is the place to start.

FAQ

How does a hot tub heat pump work?

It moves heat rather than making it — pulling warmth from the outside air and pushing it into your water, like a fridge running in reverse. That's why one unit of electricity can deliver three to five units of heat, instead of the one-for-one you get from a resistive heater.

Is a hot tub heat pump an air source heat pump?

Yes. A hot tub heat pump is an air-source heat pump sized for a tub — it draws warmth from the outside air, the same principle as the air-source heat pumps that heat houses. That's what lets it deliver several units of heat per unit of electricity, instead of the one-for-one a resistive heater gives.

Are hot tub heat pumps worth it?

It depends on how much you heat across the year. The more you use and heat your tub, the more a heat pump saves and the faster it pays back its higher upfront cost. Use the savings calculator to see the answer for your own tub and tariff rather than a made-up figure.

Does a heat pump work in winter?

Yes, though less efficiently than in mild weather. As the air gets colder there's less warmth to move, so the COP falls from around 3–5 toward 2–2.5 near freezing. That's still a big improvement on a resistive heater, which stays stuck at one-for-one all year.

Hot water needn't cost the earth — and it starts with the heater you use.