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What does ΔT, Delta T, and DT mean and why are some 50oC and others 60oC when it comes to radiators?

Hello, we thought we'd tackle a slightly thorny issue with radiators today. Heat outputs.

Despite there being the European directive EN442, there remains plenty of confusing information regarding how radiators perform and how much heat a radiator is truly providing. This post is simply a layman's overview of how radiators are measured and calculated for output.

The first thing we need to understand is that two exact same radiators can offer different heat outputs depending on the system they are operating on. The reason is that heating systems can be set at different temperatures. So how do we know if a radiator is giving enough output at the temperature our boiler runs at?

EN442 came out in the late 90s with the plan of standardising radiator performance across Europe. The method is simple. We take a radiator and put it on a heating system operating at 75oC. The water then leaves the radiator at 65oC with us looking at achieve an ambient (room) temperature of 20oC. this is referred to as  75/65/20 - Delta T 50oC or ΔT 50oC or DT 50oC. This is the standard required by the EU.

Sadly, it doesn't end there. Because boilers can be adjusted to run hotter and the fact that older boilers run at an optimum of 90oC (Delta T 60oC) we then have an issue that your radiators can in fact offer more output than this benchmark of 75oC. This has created a loophole for the industry and very misleading issue for consumers who don't know what they're supposed to be looking at.

There are many manufacturers and retailers offering outputs at  Delta T 60 and in some cases, where our suppliers have provided published outputs, we've used the 90oc calculation, (although we are trying to wean ourselves off this, ha!). It is very tricky as its very difficult to inform the end user (this is the entire point of this post) about this issue. We've had customers call us asking why we offer the exact same radiator as a competitor, but ours offer less heat. Ultimately, Delta T 50oC should be the figure you're looking for. If you need to work out the true calculation from Delta T60, you divide by 1.264.

If you want to read more on the science of this, please see our page here.

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