How big do heat pump radiators need to be?

Key takeaways

• Heat pump radiators are still standard radiators sized to accommodate the lower flow temperatures of heat pumps.
• Several factors influence the correct radiator size including room size, heat loss, desired temperature, and ambient conditions.
• A heat demand and heat loss calculation is key to ensuring that radiators are sized correctly.

Heat pumps are gaining traction as an eco-friendly, energy-bill-reducing alternative to gas boilers, but ensuring your radiators are correctly sized to accommodate their lower flow rates is crucial for achieving high efficiency.

It's important to note that a heat pump radiator is still a standard radiator, just sized appropriately for optimal system performance. Here's what you need to know to get the most out of your air source heat pump.

Key factors in sizing heat pump radiators

The size of your heat pump radiator plays a critical role in the efficiency and comfort of your home’s heating system.

Heat pumps, unlike gas boilers, work at lower flow temperatures - typically between 35°C and 55°C - while gas boilers operate at much higher temperatures, usually around 70°C to 80°C. This lower operating temperature means heat pump radiators need to be larger to provide the same cosy indoor temperatures that traditional systems deliver with smaller radiators.

When determining the correct radiator size, a heat pump installer will consider the following factors:

1. Room size and shape: Larger rooms or those with unusual layouts will require bigger radiators to ensure proper heat distribution.
2. Heat loss: Factors like wall insulation and window type affect heat retention. Thicker walls or double glazing reduce heat loss, impacting the size of the radiator required.
3. Desired room temperature: The warmth you want in your space dictates how much heat the radiator must provide.
4. Flow temperatures: Since heat pumps operate at lower flow temperatures, radiators must be larger to compensate for the reduced heat output.
5. Ambient temperature: Colder regions demand higher radiator output, making proper sizing even more critical.

By accounting for these factors, a heat pump installer can perform a heat loss calculation and recommend the right size and type of radiator to meet your home’s specific needs.

Understanding heat pump radiators

Heat pumps, especially air to water heat pumps, are becoming a popular choice for more sustainable, cheaper home heating. However, as we’ve touched on, heat pumps operate at lower flow temperatures than gas boiler heating systems. This lower temperature means your heat pump radiator needs to be larger to distribute the same amount of heat.

In fact, radiators used with heat pumps are often about 2.5 times larger in BTU (British Thermal Unit) output and up to 30% bigger in size compared to those used with gas systems.

There are several types of radiators that are typically used in home heating systems, each with varying levels of efficiency, including:

• P1 (Type 10): 1 radiator panel, no convection fins.
• K1 (Type 11): 1 radiator panel, 1 set of convection fins.
• P+ (Type 21): 2 radiator panels, 1 set of convection fins.
• K2 (Type 22): 2 radiator panels, 2 sets of convection fins.
• K3 (Type 33): 3 radiator panels, 3 sets of convection fins.

The more panels and fins a radiator has, the more surface area it provides for heat exchange, meaning it can deliver more heat at lower flow temperatures. Due to their size, we typically install K2 radiators with our Aira Heat Pump systems, but if a room has a very high heat demand we use a K3.

Importance of proper sizing

Selecting the right size for your heat pump radiator is essential for efficient heating. A radiator that's too small won’t be able to meet the heat demand of the room, leading to higher energy bills and increased wear on the heat pump. On the other hand, an oversized radiator can take up too much physical space, cause inefficiencies and unnecessarily drive up costs.

That’s why, following a free home energy assessment, our Clean Energy Experts and Designers will perform a heat demand and heat loss calculation. During these, they will assess the specific needs of your home, taking into account:

1. Room size
2. Insulation
3. Desired indoor temperature

They will also ensure the flow temperatures are optimised for your system, guaranteeing that the heat distribution is even. This step helps determine the ideal type of radiator to efficiently warm your space while keeping energy costs low.

Learn more about how heat pumps work with radiators.