How to Calculate the Right R290 Refrigerant Charge for Peak Heat Pump Efficiency

Why a Precise R290 Refrigerant Charge Guide Matters

You’ve just installed an air source heat pump. You’ve picked eco-friendly propane (R290) for its low global warming potential. Nice choice. But here’s the catch: too little refrigerant and your heat pump slugs along. Too much and you risk damage—or worse, safety incidents. This R290 refrigerant charge guide shows you how to hit that sweet spot every time.

• Efficiency: Get every ounce of energy out of R290.
• Cost savings: Avoid higher electricity bills from undercharged systems.
• Safety & compliance: Stick to the IEC 60335-2-40 standard—max 150 g per circuit in Europe.

Understanding R290: The Eco-Friendly Champion

Propane, technically labelled R290, is turning heads in the HVAC world. Why? Three big reasons:

1. Low GWP: A Global Warming Potential of just 3.
2. High efficiency: Better heat transfer than many synthetic refrigerants.
3. Regulatory push: Governments love zero-carbon refrigerants.

But don’t let its friendly footprint fool you. It’s flammable. You must respect the rules: 150 g maximum in sealed circuits. Larger systems use multiple loops, each under 150 g. Simple. But only if you calculate correctly.

Key Factors in the R290 Refrigerant Charge Guide

Getting the right refrigerant charge isn’t guesswork. It’s a mix of maths, manufacturer specs and practical know-how.

1. Heat Pump Capacity

• Smaller units (5–8 kW): Typically need 200–300 g total.
• Medium units (8–16 kW): 300–600 g.
• Larger units (>16 kW): Split across two or more circuits.

Tip: Always check the unit’s data plate. It shows the recommended charge for each circuit. Follow it to the letter.

2. Pipe Length & Diameter

Longer pipe runs trap more refrigerant. Larger diameters hold more, too.

• Standard 6 mm pipe: ~20 g per metre.
• Standard 8 mm pipe: ~30 g per metre.

Calculate:
Required charge = (Pipe length × charge per metre) + internal coil charge.

Example:
20 m of 8 mm pipe = 20 m × 30 g/m = 600 g
Plus 100 g in the evaporator coil = 700 g total
Split across two circuits = 350 g each → exceeds 150 g → redesign needed.

3. Evaporator & Condenser Coil Volume

Most manufacturers publish coil charge data. If yours doesn’t, weigh the coil’s internal volume:

• Volume in litres × 550 g/litre = coil charge.

4. Ambient Conditions

Charging in cold weather? You’ll register different pressures. Always follow pressure–temperature charts for R290.

Step-by-Step R290 Refrigerant Charge Guide

Let’s walk through a full calculation:

1. Gather data:
   – Pipe length
   – Pipe diameter
   – Coil volume (or manufacturer data)
   – System capacity (kW)

2. Calculate pipe charge:
   – e.g. 15 m × 25 g/m = 375 g.

3. Add coil charge:
   – e.g. 80 g (from spec sheet) → 455 g total.

4. Divide into circuits:
   – 455 g ÷ 3 circuits = ~152 g per circuit.
   – Exceeds 150 g? Redesign for four circuits: 455 g ÷ 4 = 113.75 g each.

5. Charge on site:
   – Use a precision scale.
   – Record ambient temp & pressures.
   – Adjust per manufacturer’s valve‐set procedures.

6. Verify performance:
   – Monitor superheat/subcooling.
   – Aim for superheat: 5–10 K (cold side).
   – Subcooling: 3–8 K (hot side).

Stick this system in your pocket. It’s the core of the R290 refrigerant charge guide.

Common Pitfalls & How to Avoid Them

Even pros slip up. Here are top mistakes:

• Overcharging: Looks safe until pressures spike.
• Undercharging: Leads to weak heating/cooling.
• Ignoring coil data: Never assume coil volume.
• Skipping safety checks: R290’s flammability demands care.

Always run a leak‐test after charging. A simple soap bubble test or electronic detector works wonders.

Learn more about R290 heat pumps

How The Heat Pumps UK Ensures a Perfect R290 Charge

At The Heat Pumps UK, we don’t wing it. We offer:

• Expert installation and maintenance services.
• Strict adherence to IEC 60335-2-40.
• Tailored system designs to keep charges under 150 g per circuit.
• Flexible finance options and government grant assistance.

Our Maggie’s AutoBlog may write SEO articles, but our engineers are all about real‐world performance. We’ll run the numbers, adjust for your pipe layout, and even train you on routine checks. No guesswork.

Benefits of a Properly Charged R290 System

Hit the nail on the head and you’ll see:

• Energy savings: Up to 25% lower bills.
• Longevity: Less wear on the compressor.
• Comfort: Steady heat output, no cold spots.
• Eco-cred: Low GWP locks in green credentials.

Frequently Asked Questions

What if my system needs more than 150 g?

Use multiple refrigerant circuits. Many modern heat pumps come pre-designed for this. If yours doesn’t, talk to our design team.

Can I charge R290 myself?

Only if you’re certified in flammable refrigerants. Otherwise, call a professional—safety first.

How do I know I’ve charged it right?

Measure superheat and subcooling. Match them to the manufacturer’s spec. If they align, you nailed it.

Conclusion

Calculating the right charge is a blend of science and know-how. Follow this R290 refrigerant charge guide, lean on manufacturer data, and partner with experts like The Heat Pumps UK. That’s how you keep efficiency high, costs low and carbon footprints shrinking.

Contact our expert team today