Posted: Friday, August 23, 2024
When choosing a radiator, it’s important to consider more than just its appearance. Calculating the appropriate BTU output prevents under or overheating and the choice of radiator material impacts heat retention. At Trads, we’re often asked, ‘Do cast iron radiators take longer to heat up?’. Compared to modern steel or aluminium options - yes, they do. However, this can be easily managed with prior planning. To appreciate the benefits and differences of the main types of radiator material - cast iron, steel and aluminium - let’s delve into the science behind each metal.
Why Do Cast Iron Radiators Take Longer To Heat Up? - Thermal Conductivity
Cast Iron
Thermal conductivity is a measure of how well a material can conduct heat. Cast iron has a lower thermal conductivity than steel and aluminium meaning it takes longer for heat to spread throughout the material when hot water flows through each section.
Steel & Aluminium
Steel and, in particular, aluminium, have higher thermal conductivity, which allows them to heat up quickly. This means that when these materials are used in radiators, they transfer heat more rapidly from the hot water inside to the surface of the radiator, leading to quicker heating.
Cast Iron - Heat capacity is the amount of heat required to raise the temperature of a substance by a certain amount. Cast iron has a high heat capacity, meaning it can absorb and store a significant amount of heat before its temperature rises. This property contributes to the longer time it takes to heat up, but also to the ability to retain heat longer once it is hot.
Steel & Aluminium - Steel and aluminium have lower heat capacities compared to cast iron. This means they require less energy to increase in temperature, allowing them to heat up faster. However, they also lose heat more quickly once the heat source is removed.
Cast Iron - Cast iron is denser than steel and aluminium. Density affects how much material there is to heat up within a given volume. The higher density of cast iron means that there is more mass to heat, which contributes to the longer warm-up time. However, this also means that, once heated, cast iron radiators can continue to emit heat for a longer period, even after the heating system is turned off.
Steel & Aluminium - Steel is less dense than cast iron, and aluminium is even less dense than steel. With lower densities, these materials have less mass to heat within a given volume, which translates to quicker heating times.
Surface area directly affects a radiator's BTU output. This unit of measurement determines how much heat is needed to adequately warm a room, making it an important factor to consider regardless of the radiator material. The majority of cast iron radiator designs use multi-column structures that significantly increase the radiator’s surface area and therefore BTU output. Do cast iron radiators take longer to heat up when they contain additional columns? Yes, but larger radiators made from any material take longer to reach their full operating temperature compared to smaller radiators. In contrast, steel and aluminium radiators are typically designed with flat panels or slimline profiles that have less surface area but make up for it with higher thermal conductivity, allowing for quicker heat distribution.
To find smaller radiators with a large BTU output or vice versa, use Trads’ BTU calculator. Alternatively, call our helpline to speak with one of our experienced team members who will be more than happy to help.
Do cast iron radiators take longer to heat up? Yes. Should this be a reason not to purchase one? Definitely not! The Trads team manufacture over 50 styles and heights of cast iron radiators in their Lincolnshire-based factory. To view the full collection, visit our website, book a factory tour or visit our showroom.
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