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Do I Need a Hot Water Cylinder with an Air Source Heat Pump?
- Lindo Mavuso
- Oct 1
- 3 min read
If you're thinking about switching to an air source heat pump, there's a good chance you’re also asking:
“Wait… does that mean I need a hot water cylinder too?”
The short answer? Yes, in most cases, you do.
But don’t let that put you off. Because here’s the thing:
Unlike combi boilers that heat water instantly on demand, air source heat pumps work differently; they’re slower, smarter, and much more efficient when paired with hot water storage.
In this quick guide, we’ll explain:
Why do heat pumps need cylinders
What kind of cylinder do you need (and where it goes)
Whether you can avoid one (in special cases)
And how this setup actually saves you more money over time
Already comparing options? Learn more about how we design ultra-efficient heat pump systems here →
Let’s break it down.
Why Heat Pumps Need a Cylinder in the First Place
If you’re used to a combi boiler, the idea of adding a hot water cylinder might seem like a step backwards.
But with an air source heat pump? It’s not just a requirement, it’s part of what makes the system so efficient.
Lower Flow Temperatures = Stored Heat
Gas boilers heat water fast, often at 70–80°C, so they can give you hot water on demand.
But air source heat pumps are designed to run at lower flow temperatures, typically around 35–55°C. That means:
They heat water more slowly
And do it more efficiently, especially when used with stored water
So instead of firing up instantly every time you open a tap, the system stores hot water in advance, ready when you need it.
Why This Is a Good Thing
You heat water when energy is cheapest (e.g., using smart tariffs)
You can store solar energy and use it for hot water later
Your system runs steadily instead of ramping up and down, which extends lifespan and lowers bills
In short, cylinders aren’t just “old school”, they’re smart when paired with a modern heat pump.
Explore more about system design:
Air Source Heat Pump Overview →
What Type of Hot Water Cylinder Do You Actually Need?
When it comes to pairing a heat pump with a hot water cylinder, size and spec matter. It’s not one-size-fits-all.
Here’s what you need to know to get it right.
What Size Cylinder Should I Get?
The right cylinder depends on how much hot water your household uses. For example, we plan based on 45 liters per person.
This allows you to:
Run baths, showers, washing machines, and taps, without running out
Keep the system efficient by avoiding oversizing
Pro Tip: Oversizing can cause heat loss. Undersizing leads to cold showers. We help you get this balance right in every installation.
Where Will the Cylinder Go?
Most modern cylinders are slimline and can fit into standard airing cupboards or utility spaces.
As a general guide:
Space needed: around 2000mm x 900mm
Needs to be close to the hot water outlets (for efficiency)
May be combined with a buffer tank or immersion heater if needed
And yes, cylinders can be neatly tucked out of sight without impacting performance.
What About Cold Water Storage?
In most cases, you'll use an unvented cylinder, which takes cold water straight from the mains and heats it. No need for an extra tank in the loft.
This gives you:
Better water pressure
More flexibility on placement
Simpler plumbing layout
For more information:
Final Thoughts
For most homes in the UK, pairing an air source heat pump with a well-sized, well-insulated hot water cylinder is the most efficient, cost-effective, and grant-eligible route.
It’s not just about what works, it’s about what works best long-term.
And that’s where Puraflow comes in.
Recap: Do I Need a Hot Water Cylinder with a Heat Pump?
Question | Answer |
Is a cylinder required? | Yes, in most standard systems |
Can I avoid it? | Only with compact or air-to-air systems |
What size? | 120–250L+, depending on household size |
Where does it go? | Cupboards, utility rooms, airing spaces |
Does it help with grants? | Absolutely, it’s part of most MCS-compliant installs |
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