Do I need to install New Radiators with a Heat Pump

Do Heat Pumps Need New Radiators

So, you're planning to install a heat pump to cut your energy consumption and reduce your carbon footprint, but your concerned that your existing radiators might not keep your home warm enough. Let's address the confusion around heat pumps and radiators to help you plan effectively.

Heat pumps operate differently from traditional boilers, using lower flow temperatures (typically 35-55°C) compared to boilers (often 60-80°C). This difference will reduce the heat output of existing radiators, especially in older or less insulated homes, this isn't a flaw. With proper radiator sizing and system design, you will ensure your heat pump delivers consistent warmth efficiently.

Understanding Heat Pump Compatibility with Existing Radiators

How Heat Pumps Differ from Traditional Boilers

Heat pumps absorb heat from air, ground, or water using a refrigerant which is compressed to increase the temperature and warm your home. This produces lower-temperature heat compared to traditional boilers, which burn fuel for instant direct, high-temperature heat.

Heat pumps achieve their best efficiency, measured by the Seasonal Coefficient of Performance (SCOP) - the amount of heat produced per unit of electricity used over an entire heating or cooling season - at lower water temperatures. This means they use less energy to keep your home warm compared to boilers operating at higher temperatures.

Impact on Heating Performance

• Radiator output: At lower flow temperatures, radiators emit heat more gradually, maintaining steady warmth.

• Heating cycles: Heat pumps run longer, continuous cycles to avoid inefficient on/off operation, unlike boilers short, high-heat bursts.

• Energy efficiency: Lower temperatures improve SCOP (typically 3.5-4.0), reducing energy use compared to mainstream boilers.

Proper radiator sizing is critical to ensure consistent heat output without forcing the heat pump to cycle on and off, which can reduce efficiency and strain the system.

Professional Heat Loss Calculations: The Key to Efficiency

From December 2024, the Microgeneration Certification Scheme (MCS) references the BS EN 12831-1:2017 standard for heat loss calculations under MIS 3005-D, replacing BS EN 12831:2003. This ensures accurate heating system designs tailored to your home.

What Are Heat Loss Calculations?

Heat loss calculations determine how much heat your home loses through floors, walls, windows, roofs, and ventilation. An experienced surveyor conducts a room-by-room survey (typically 2-3 hours, depending on property size) to measure:

• Room dimensions and ceiling heights.

• Insulation levels

• Window and door areas.

• Ventilation rates and airtightness (further testing can be carried out)

The updated standard accounts for modern insulation and ventilation practices, ensuring radiators are sized to match your home’s heating needs. The MCS online heat load tool supports these calculations, ensuring compliance and preventing oversized or undersized systems.

Why It Matters

Accurate calculations ensure radiators provide enough heat at lower temperatures without requiring the heat pump to cycle excessively. This maintains efficiency, comfort, and MCS compliance for heat pump installations.

Evaluating Your Current Radiators

Before switching to a heat pump, a heat loss assessment will determine whether your existing radiators can deliver sufficient heat, at a lower flow temperature.

The surveyor will check radiator size, type (e.g., single or double panel), and heat output ratings at Delta T (ΔT) (the temperature difference between the radiator and the room).

To get a rough idea of how your current radiators might perform with a heat pump, you can try lowering your boiler’s heating flow temperature to 50-55°C (not hot water temperature), to mimic a heat pump’s operating range.

Also, when running your existing boiler feel the temperature at the bottom of the radiator in the middle, level with skirting board as radiators can become clogged and less efficient

Monitor your home’s comfort over a few days to see if the radiators provide enough warmth. Keep in mind that this test is only indicative, as heat pumps run continuously, unlike boilers, and performance depends on your home’s insulation.

A professional heat loss calculation remains essential to confirm radiator suitability.

Radiator Solutions for Heat Pump Systems

Optimising Existing Radiators

To maintain the steady operation of your heat pump, try to avoid controls (such as TRV's or individual room stats) that turn radiators on and off frequently. Instead, focus on ensuring radiators are sized correctly for your home’s heat loss, as determined by a professional survey. Existing radiators can sometimes work if:

• Additional radiators are added in high-demand areas to distribute heat evenly.

• The home is well-insulated, or more insulation is added, reducing the overall heat demand.

If existing radiators are undersized, they may force the heat pump to run at higher temperatures, reducing efficiency and increasing energy costs.

When Replacement Makes Sense

If your current radiators can’t deliver enough heat at lower temperatures, replacement is often the best solution.

Upgrading heat emitters at the same time as installing a heat pump also offers additional savings as this can be carried out at 0% VAT.

Alternative Solutions: Beyond Traditional Radiators

For optimal heat pump performance you could consider alternatives that complement their steady, low-temperature operation:

• Underfloor heating: Operates efficiently, providing radiant heat that minimises cold spots and can help reduce energy use.

• Fan coils: Effective for large spaces and can provide cooling. Also typically smaller than a radiator with the same output.

Conclusion: Making the Right Choice for Your Home

Choosing the right heat pump and heat emitter combination requires a professional assessment. An experienced surveyor will perform a heat loss calculation to evaluate your home’s insulation, window types, room sizes, and fabric. This ensures radiators are sized to support continuous heat pump operation, avoiding efficiency losses from cycling.

Take Action Today

Consult an MCS-certified installation company for a tailored heat loss calculation. Visit mcs.org.uk to find qualified professionals. Investing in a professional assessment ensures your heat pump system delivers consistent comfort and maximum efficiency for years to come.