Understanding Delta T & What It Means for Your Heat Output
When purchasing radiators for your home, it's no secret that understanding the heat output they provide and whether it's sufficient for the space they will be installed in is important. With various numbers and technical heating terms to decipher, it can be a little overwhelming when it comes to making the correct decision. Alongside BTU, Delta T is another important figure to consider when shopping for radiators.
In this blog, we'll explain how to understand Delta T and what it means to you as a consumer.
What Is Delta T and What Does It Mean?
Delta T, or ∆T as it is commonly abbreviated, specifically relates to the difference in temperature between the water circulating in the central heating system and that of the ambient room temperature. For example, if the ambient room temperature is 30ºC and the mean water temperature inside the radiators is 70ºC, the Delta T or ∆T value is calculated as 70ºC - 30ºC = 40ºC.
Why are Delta T Values Important to Know?
Delta T 50° is the UK standard for all domestic gas boilers and is set to allow professionals, end-users and consumers alike, to make fair and reasonable comparisons of radiator and towel rail outputs from various suppliers and across a mix of product types. This test is based on a set of parameters that replicate the temperature of the water coming from the boiler/heat source (flow temperature), the desired room temperature and the return temperature of the water.
However, if any of these factors are changed it will affect the amount of heat given off by a radiator meaning you may need a different size. For example, if your flow temperature is lower than 80ºC, then the radiator will provide less heat. With today’s new boilers and renewable heat sources, a lot of heating systems are producing a flow temperature of 55ºC or lower which will mean a delta T of 30 (less heat in = less heat out!).
Our simple conversion tool below can tell you how much heat your chosen radiator will produce based on this new Delta T so you can find an alternative size if needed.
Delta T Correction Factors - Delta T 50°C
When comparing radiators/towel rails, ensure you are being quoted Delta T 50°C, furthermore, look for the MARC logo (Manufacturers Association of Radiators and Convectors) and be sure to request the Declaration of Performance, conducted by an accredited body.
A Delta T correction factor allows end-users and professionals to find out the actual output of a radiator or towel rail in the range of Delta T variations. Our Delta T Calculator has been designed to efficiently calculate this based on input at Delta T 50°, alternatively, you can use the listed correction factors below, also based on Delta T 50°C:
Delta T | Correction Factor | Delta T | Correction Factor |
75° | 1.69 | 40° | 0.75 |
70° | 1.55 | 35° | 0.63 |
65° | 1.41 | 30° | 0.51 |
60° | 1.27 | 25° | 0.41 |
55° | 1.13 | 20° | 0.3 |
50° | 1 | 15° | 0.21 |
45° | 0.87 | 10° | 0.12 |
Example:
Assuming a radiator or towel rail has a heat output of 1000 Watts at ΔT (Delta T) = 50°C.
At ΔT (Delta T) = 60°, the output would be 1000 Watts x 1.27 (from the table above) = 1270 Watts. Alternatively, at ΔT (Delta T) = 40°C, the output would be 1000 Watts x 0.75 = 750 Watts.
Still Need Help?
Is Delta T still leaving you a little perplexed? If you have any further queries or are still unsure, please don't hesitate to reach out to our customer service team!
