What Size Heat Pump Do You Need for Your Pool?

If you’ve ever slipped into your pool that feels more like an ice bath, you’ll know how important a good heating system is. The right pool heat pump size keeps your water at the perfect temperature without chewing through electricity.

But what size heat pump do you need for my pool?” This pool heat pump sizing guide will walk you through the essentials, so you can heat your pool efficiently, save on energy, and enjoy more swim days in comfort.

Why the Right Size Matters

Pick a heat pump that’s too small and you’ll shiver, too big and you’ll overspend, the right size hits the sweet spot for comfort and cost. Here’s why it matters:

• Undersized heat pump: It will struggle to keep up, especially during cooler months or windy days. You’ll end up running it longer, which means higher power bills and a pool that never quite reaches your ideal temperature.
• Oversized heat pump: While it might heat faster, you’ll pay more upfront, potentially waste energy, and risk short-cycling (turning on and off too frequently), which can shorten the pump’s lifespan.

The sweet spot is a heat pump that matches your pool’s volume, local climate, and usage habits.

Key Factors to Consider When Choosing a Heat Pump

Pool Volume

First, work out your pool’s water volume; it’s the foundation for pool heat pump sizing.

• Rectangular pool: Length × Width × Average Depth × 1,000 = litres
• Circular pool: π × Radius² × Average Depth × 1,000 = litres
• Convert litres to cubic metres by dividing by 1,000. For example, a 5 m × 4 m pool with an average depth of 1.5 m holds around 30,000 litres, or 30 m³.

Climate

New Zealand’s weather varies a lot between regions. A pool in Auckland may only need a moderate boost to stay warm, while one in Queenstown will need more heating capacity to counter cooler air and water temperatures, especially in shoulder seasons.

Desired Temperature

Decide on your target water temperature. The bigger the difference between your current and desired temperatures, the more power your heat pump will need. Most Kiwi pool owners aim for 26–28 °C for comfortable swimming.

Pool Cover

A pool cover is a game-changer. It can reduce heat loss by up to 35%, which means you can size down your heat pump or run it for fewer hours. Without a cover, you’ll need extra capacity to compensate for overnight cooling and evaporation.

Usage Patterns

If you swim all year round, size for your coldest month of use. If your pool is seasonal, you can opt for a slightly smaller pump as it won’t need to fight winter’s chill.

Simple Sizing Formula & Quick Reference Table

Once you’ve got your pool’s volume, adjust for climate and whether you use a pool cover. As a general rule:

• With cover: Multiply your pool volume (m³) by 0.3–0.4 to get an approximate kW size.
• Without cover: Multiply by 0.4–0.5.

Here’s a quick reference for common NZ pool sizes:

These figures are guides; local weather, pool location, and swim frequency can all shift the ideal size up or down.

How Correct Sizing Saves Money & Extends Equipment Life

A correctly sized pool heat pump is more than just an efficiency win; it’s a long-term investment in your pool.

• Lower running costs: The unit operates in its optimal range, using less electricity to maintain your set temperature.
• Fewer repairs: Overworked pumps wear out faster; right-sizing reduces strain on components.
• Consistent comfort: No wild temperature swings, just steady, enjoyable swimming conditions.

In short, you’re getting better value from every dollar spent on both energy and equipment.

Choosing the Right Model for NZ Conditions

When narrowing down models, don’t just look at the kW rating. Check for:

• High COP (Coefficient of Performance): The higher the COP, the more heat you get per unit of electricity. Look for at least 5.0+ for good efficiency.
• Corrosion resistance: Essential for coastal areas, opt for units with titanium heat exchangers and weatherproof casing.
• Trusted brands and warranties: A reputable supplier ensures you’re not just buying a heat pump, you’re buying support, spare parts, and expert advice.

At Dolphin Pacific, we supply heat pumps from trusted brands like Hayward, built for NZ’s varied climates and backed by our technical know-how.

Right Size, Right Comfort

So, what size heat pump do you need for your pool? The answer comes down to knowing your pool’s volume, your climate, your temperature goals, and whether you use a cover. Get those factors right, and you’ll enjoy warm, inviting water for longer, without blowing out your power bill.

If you’re ready to get the sizing spot-on, our team at Dolphin Pacific can help. Find your local dealer today, and start heating your pool the right way.