The Radiator Revolution Nobody Talks About

When people install heat pumps, they obsess over the unit itself - its capacity, brand, features. But the real secret to heat pump efficiency isn't the heat pump. It's what's hanging on your walls.

We learned this the expensive way. Then we fixed it. Here's our story.

Our Starting Point: Fighting Physics

Our home came with 19kW of radiator capacity (at ΔT50). For those unfamiliar with the terminology, that means our radiators could emit 19kW of heat when the water inside was 50°C hotter than the room.

This would have meant running flow temperatures of 49°C when it was -2.5°C outside - a recipe for poor efficiency and high bills.

The Uncomfortable Truth About Temperature

Here's what most people don't understand: every degree you raise your flow temperature dramatically reduces your heat pump's efficiency. It's not a linear relationship - it's exponential pain.

At 49°C flow temperature, your heat pump is working incredibly hard. The compressor is stressed, the efficiency is poor, and you're basically using an expensive electric boiler.

The Smart Solution: Upgrade First, Install Second

Before installing our heat pump, we made a strategic decision: we more than doubled our radiator capacity from 19kW to 40kW (at ΔT50).

Yes, it meant: - Bigger radiators in most rooms - Some double radiators where we had singles - A few new radiators in previously unheated spaces

But here's what happened next...

The 9°C Advantage We Built In

With our new 40kW of radiation capacity, our heat pump could deliver the same heat output with a flow temperature of just 40°C instead of the 49°C that would have been required with the original radiators.

Nine degrees. It doesn't sound like much. But in heat pump terms, it's the difference between a marathon runner and a Sunday jogger.

The Cascade of Benefits

1. Dramatic Efficiency Gains

Lower flow temperatures mean higher COP (Coefficient of Performance). Our heat pump now delivers significantly more heat per unit of electricity consumed.

2. Battery Storage Transformation

Here's the game-changer nobody mentions: with our 60kWh battery storage, improved efficiency means we can run longer on cheap electricity.

When we charge our batteries at 6p/kWh overnight, that stored energy now heats our home for far longer. Less draw at 28p/kWh during peak times means massive savings.

3. True Comfort at Last

Lower flow temperatures mean: - No more hot and cold spots - Consistent, gentle warmth - Silent operation (no more expansion noises) - Even heat distribution throughout each room

The Hidden Challenge: Pipe Sizing

Here's something installers rarely discuss: when you run lower flow temperatures with a small temperature differential (ΔT5), you need more water flow to carry the same amount of heat.

Your existing pipes might become a bottleneck. Fortunately, our house was built in the golden age of heating when installers used generously sized pipework. No 1980s microbore nonsense here - our substantial pipes could easily handle the increased flow rates.

If you're not so lucky, you might need to check flow rates and potentially upgrade some pipe runs. There's no point having massive radiators if your pipes can't deliver enough warm water to them.

The Maths That Matters

Let's talk real numbers:

Before: 19kW radiators, 49°C flow, fighting physics After: 40kW radiators, 40°C flow, working with physics

The result? Our heat pump now runs in its optimal efficiency zone almost constantly. During those -2.5°C cold snaps, we're warm, comfortable, and not dreading the electricity bill.

The Investment Perspective

Upgrading radiators before installing a heat pump is one of the smartest investments you can make:

• You design your system for optimal efficiency from day one
• Your heat pump operates in its sweet spot from the start
• No retrofit disruption after your heat pump is installed
• You avoid ever experiencing poor efficiency

This proactive approach means you never pay the "inefficiency tax" of undersized radiators. With electricity prices where they are, starting with proper radiator capacity is essential.

Lessons Learned

1. Radiator capacity is not optional - It's the foundation of heat pump efficiency
2. Every degree matters - Lower flow temperatures compound into major savings
3. Comfort improves with size - Bigger radiators mean better heat distribution
4. Pipes matter too - Don't let narrow pipes bottleneck your upgraded system
5. Battery storage amplifies savings - Efficiency gains multiply when you're storing cheap electricity

The Path Forward

If your heat pump is running flow temperatures above 45°C, you're leaving money on the table. Every degree you can drop that temperature improves your COP and reduces your running costs.

The formula is simple: - More radiator surface area = Lower flow temperatures - Lower flow temperatures = Higher efficiency - Higher efficiency = Lower bills + Better comfort

Your Next Steps

1. Check your current flow temperature - If it's above 45°C at design temperature, you have room for improvement
2. Calculate your existing radiator output - Most are rated at ΔT50, but you need to know their output at lower temperatures
3. Identify upgrade opportunities - Which rooms could benefit from larger radiators?
4. Don't forget the pipes - Ensure your system can handle increased flow rates

The Bottom Line

We doubled our radiator capacity and dropped our flow temperature by 9°C. The improvement in comfort and efficiency has been transformational.

Your heat pump is only as good as the radiators it's connected to. Give it the radiators it deserves, and it will reward you with efficiency that seemed impossible before.

Want to optimize your heat pump system for maximum efficiency? Join our early access program and discover how intelligent control can work with your upgraded radiators to deliver even better results.