Hot tub heat pump vs electric heater

Hot tub heat pump vs electric heater: the honest comparison

Nearly every inflatable and foam hot tub — Lay-Z-Spa, CleverSpa, Intex, Wave Spa and the rest — comes with a built-in electric heater. It works, it's simple, and it's also the most expensive way to keep the water warm. An air-source heat pump does the same job far more efficiently, but it costs more upfront and it isn't magic in the depths of winter.

This guide lays the two side by side, honestly, so you can decide which suits you. We won't quote a fixed payback figure — that depends on your tub, tariff and habits, so we'll point you to the savings calculator for that. If you want the wider picture on costs first, see our hot tub running costs guide.

How each one actually heats the water

The built-in electric heater is a resistive element — essentially a large kettle element sitting in the water flow. Electricity passes through it, it gets hot, the water gets hot. It's about 100% efficient, so one unit of electricity gives you one unit of heat. That's a COP (coefficient of performance) of 1, and it's the ceiling — resistive heating can't do better than that.

An air-source heat pump doesn't create heat, it moves it. It uses a small amount of electricity to run a compressor that harvests warmth from the outside air and pumps it into the water — the same principle as a fridge, run in reverse. Because it's moving heat rather than making it, each unit of electricity delivers several units of heat. That's why it's so much cheaper to run.

The efficiency comparison (COP)

COP is simply "units of heat out per unit of electricity in". Higher is better. Here's the honest picture — note the heat pump's winter drop, because that matters:

Heating method	Typical COP	What it means
Built-in resistive heater	1 (all year)	1 unit of electricity → 1 unit of heat. No better in summer, no worse in winter.
Air-source heat pump — milder weather	~3–5	Same heat for roughly a third to a fifth of the electricity.
Air-source heat pump — near freezing	~2–2.5 (treat winter as ~2–3)	Efficiency falls in the cold, but still uses around half the power of resistive.

These are efficiency ratios, not a promise of a specific bill. Your real numbers depend on weather, water temperature and how you run the tub.

Pros and cons, side by side

Built-in electric heater

• For it: already fitted, nothing to buy, simple, silent, and it doesn't care how cold it is outside — COP 1 in July, COP 1 in January.
• Against it: it's the most expensive method to run, full stop. It's also typically slower to heat, and on some tubs it won't run the heater and the massage jets at the same time.

Air-source heat pump

• For it: dramatically lower running cost for the same heat, and it heats roughly twice as fast. App-controlled, and it retrofits to the tub you already own.
• Against it: it costs more upfront, it's a unit that sits beside the tub, and it makes a gentle fan/compressor hum while running (about the level of an outdoor AC unit). Its efficiency drops in freezing weather — still ahead of resistive, but less dramatically.

Are hot tub heat pumps worth it? Who each suits

A heat pump makes most sense if you use your tub regularly or keep it warm much of the year, you want to cut running costs and carbon, and you're happy with a one-off spend to get long-term efficiency. The more heat you ask for over the year, the more the COP advantage compounds.

The built-in heater may be fine if you only dip in occasionally, drain the tub between uses, or aren't ready to spend on new kit. There's no shame in it — for very light use the running cost stays modest simply because you're barely heating.

Our retrofit heat pump for Lay-Z-Spa and similar tubs is designed exactly for this switch: it does the built-in heater's job, far more efficiently, on a tub you already have. Add solar and battery and you can push running costs lower still — that's covered in our solar hot tub kit guide.

More than a heat pump: a self-managing renewable system

A heat pump versus an electric element is a fair fight to have — but it undersells what we actually build. The heat pump is only one of four parts. Alongside it sits a 610W bifacial solar panel, a smart power box that stores that solar in its own battery, and a smart switch box that safely swaps between your free renewable power and household mains.

An electric heater can only ever do one thing: pull expensive mains electricity and turn it into heat. Our system generates, stores, and manages its own energy — then chooses the cheapest greenest source for every heating session automatically. The heat pump handles the efficient warming; the rest of the system makes sure it's sipping from your solar and battery long before it ever touches the grid.

So the honest comparison isn't "pump or element." It's "a swapped-out heater" versus "a small power station in your garden that runs itself." If that sounds like a step up, our solar hot tub kit page walks through the whole setup.

What about payback?

Honestly? It depends on you — your tariff, how often you soak, how well the tub is insulated and how cold your winters run. Anyone quoting a single payback figure for every tub is guessing. Rather than invent one, we built a savings calculator you can put your own details into, and we monitor real, measured performance on our own kit so the assumptions behind it are grounded. If you'd like a hand working it through, drop us a line.

Frequently asked questions

Are hot tub heat pumps worth it in the UK?

For regular users, usually yes — the built-in heater runs at COP 1 while a heat pump manages around 3–5 in mild weather and 2–3 in the cold, so it uses a fraction of the electricity for the same heat. Whether the upfront cost pays back in a timeframe you're happy with depends on your usage and tariff, which is what the calculator is for.

Do heat pumps still work in winter?

Yes, but less efficiently. As the air gets near freezing, COP falls to roughly 2–2.5. That's still meaningfully better than the built-in element's COP of 1 — you're using about half the power for the same warmth — but the gap narrows in the coldest spells. We think it's important to be upfront about that rather than pretend efficiency holds steady all year.

Are heat pumps noisy?

They make a gentle hum from the fan and compressor while running, similar to an outdoor air-conditioning unit — noticeable up close, easy to ignore from a few metres away. The built-in electric heater, by contrast, is silent. For most gardens the sound isn't an issue, but it's worth knowing before you buy.