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Trads cast iron radiators combine classic aesthetics and design features with the modern heating technologies you would expect on a quality radiator. We know that for many people reading this, it may be the first time you’ve bought a cast iron radiator and you may have some questions. Keep on reading to find the answers to all of our frequently asked questions.

Cast iron heat radiator output and units of measurement

You're buying a cast iron radiator because you want to heat your home (and with a Trads radiator you’ll be enhancing your interior decor too). So, it’s important to understand the standard unit of measurement that is used to show how much heat a radiator gives off (also known as the 'heat output'). That standard of unit is the BTU. It stands for British Thermal Unit and it’s a unit of energy. 

To put BTUs into context, one BTU is approximately the same amount of energy as the heat given off by a single wooden kitchen match. 

At Trads we sell our radiators in sections. You will find the BTU of each section in the product description. So, for example, you may want to buy a radiator where each section has an output of 201 BTUs. If you buy three sections, then your entire radiator will have an output of 603 BTUs.

If you're unsure how many BTUs you will require to heat your room, please use Trads’ handy BTU calculator.

Tip - Remember to buy a radiator that has a slightly higher BTU than that required by your room. This provides you with a ‘margin of error’. Your radiator will have a bit more power than you need, but you can always turn it down.

If you’ve been browsing our radiators, you may have noticed that our product descriptions also show the Watts of a radiator as well as the BTUs. 

Whilst they may seem similar, they measure different things. 

A BTU is a unit of energy, whereas a Watt measures the rate that energy is transferred. We quote the outputs of our radiators in both Watts and BTUs to make it easy for you to determine the correct radiator sizing you need.

You may sometimes see people talking online about converting BTUs into Watts. This isn’t possible because they are very different units of measurement. Instead, what most people mean when they talk about converting BTUs into Watts is converting BTUs per hour into Watts. This conversion is sometimes written as BTU/h.

While you've been shopping around for your new cast iron radiator, you may have encountered something called a 'Delta rating'. 

BTUs are used to calculate the heat output of a radiator. However, this heat output is impacted by the temperature of the boiler supplying the radiator. Essentially, the performance of the boiler will affect the final BTU result of the radiator. 

So, in order to calculate the BTU of a radiator, manufacturers such as Trads have to make some assumptions about the temperature of the boiler supplying the radiator when we are calculating BTU figures. 

These assumptions about the temperature of the supplying boiler are known as Deltas. There are a number of different Deltas. At Trads we use two different measures - Delta 50 and Delta 60. 

Delta 50 is what European manufacturers have been using for a while. In the UK, we used Delta 60 until recently, when manufacturers such as ourselves swapped to Delta 50. 

Delta 50 is based on a much lower expected boiler temperature. It factors in things like improved boiler insulation. Whereas, Delta 60 is based on a higher boiler temperature. 

These Delta ratings are worked out as follows:

  • We take the flow out from the boiler (80ºc), and the return (60ºc). The average of these is 70ºc.
  • We then minus the room temperature of 20ºc.
  • So, 70ºc minus 20ºc = 50 Delta T.

If you are intending to use alternative flow temperatures such as a ground source heat pump, Trads can apply a correction factor to compensate for this.

We show both Deltas in our product descriptions as we realise there are many people (such as many heating engineers) who still prefer to use the older Delta 60 assumption when calculating the BTU of a radiator.

Tip - When buying a radiator, you’ll naturally want to check its BTU output. But you should also always check to see which Delta assumption this BTU rating is based on. For example, if one store is displaying their BTU ratings based on Delta 60, then their radiators will appear to be more powerful than a store which is displaying their BTU ratings based on Delta 50 (when in fact they are not). That’s why at Trads we include both Delta 50 and Delta 60 in our product descriptions so you can make a completely informed choice.

Cast iron radiators provide a far more attractive way of heating your home compared to steel radiators. Thanks to the grade of cast iron we use here at Trads, our cast iron radiators are highly conductive, radiating far more heat than a steel radiator would. So, by choosing a cast iron radiator you’ll not only benefit from a superior aesthetic and finish, but you’ll benefit from superior performance too. 

Trads' cast iron radiators also stand out from competitors thanks to the way in which we design them to hold a larger volume of water. With a higher volume of water and a larger surface area, you’ll be staggered by the heat output of a Trads cast iron radiator.

Thanks to their longevity, cast iron radiators are certainly environmentally friendly. We design our radiators to last for decades. By the time you have installed and replaced a steel radiator three or four times, a Trads cast iron radiator will still be going strong, meaning fewer raw materials are used in the long-term. 

Thanks to their superior heat output, cast iron radiators are more environmentally friendly than standard steel radiators which cool down and lose heat quickly. 

But, that’s not all. The high-quality cast iron used by Trads not only heats up quickly, but goes on to radiate heat for a long period of time - meaning your room heats up and stays warm for far longer than with a steel radiator. 

The heating characteristics of Trads cast iron radiators also means they work really well with alternative energy sources such as ground source pumps and solar powered heating systems. 

At Trads we also offer a lifetime guarantee on all of our cast iron radiators, so you can be sure that your radiator will go on and on and on. 

Additionally, all of our radiators go through a 60 step quality assurance process and adhere to ISO 9001:2015, BS: EN 442-2 and carry the CE mark.

Radiator Valves Guide

A manual valve is simply an angled tap on your radiator which is used to turn it on and off. In a manual radiator valve system the radiator control is based on a thermostat located away from the radiator (not located on the body of the radiator). With a manual radiator valve, you control the temperature of the radiator by turning the valve to a greater or lesser extent.

Thermostatic valves on the other hand, feature an in-built temperature sensor which controls the temperature of the radiator automatically. Thermostatic valves actively monitor the temperature of the room and will adjust the radiator’s heat output to maintain a consistent room temperature. With a manual valve, you’ll need to monitor the temperature of the room yourself, as the radiator will stay at the manually set temperature regardless of how hot or cold the room is. 

Cast iron radiator painting and finishing information

We understand that for many people, their new cast iron radiator purchase is part of a wider home renovation project. As such, they want to match the colour of their radiator to their overall decor. To do this, they need to colour match. 

At Trads, we provide just such a colour match service.

In addition to the 10,000 colours that we have available, our expert colour matching service can provide you with the ultimate level of customisation for your cast iron radiator. Our on-site paint and spray shop has a huge amount of experience working with customers to achieve their desired colour.

We can also provide you with up to six swatches so that you can compare our colours in the comfort of your own home. Click here to request swatches.

At Trads we offer arguably the most comprehensive paint and finishing services in the UK radiator industry. 

In addition to our 10,000 colours and colour matching service, we also offer paints from leading brands such Farrow & Ball, Little Greene, Roberson Liquid Metal and many others. 

Our paint finishes include semi-gloss, full gloss, satin and metallic. We also offer a range of polished, patina and even hand gilded finishes. 

In other words, if you have an idea about a finish for your cast iron radiator, then speak to Trads. We can accommodate almost any paint or finish you can think of!

Yes. It’s always best to view a sample of paint in person, as colours can sometimes look different online or in print. 

We are more than happy to send you up to 6 swatches so that you can see our beautiful paint options for yourself. Simply complete the short form here, and we will have colour swatches sent out to you.

In addition to our huge range of colours, we also offer a variety of different finishes which really accentuate the classic design touches of our radiators. 

However, one of the questions we regularly receive is about the difference between our various finishes. You’ll find the answers below.

Hand Burnished

A hand burnished finish is achieved using a high degree of polishing using fine ceramic abrasives. The radiator is then buffed with a stitched polishing mop. It’s a time consuming, labour intensive process, but it produces a finish which is bursting with character. It’s the sort of finish that will make your decorative radiator the centrepiece of a room. 

Satin Polish

As with the hand burnished finish, a satin polished radiator also undergoes a ceramic abrasive process. However, with a satin polish finish, the final polishing process is changed to give a subtle sheen and a wonderful antiquated quality. As with a hand burnished finish, a satin polished radiator can be lacquered which will ensure no further maintenance is required. 

Highlight Polish

With a highlight polish each section of your radiator is first painted in your colour of choice (in the case of a highlight polish, this colour is usually black as it has the most impact once polished). Once the paint process has been completed, the raised details of your radiator are then delicately polished by hand using a fine abrasive wheel. Like the hand burnished finish, this is a labour intensive process involving our craftsmen. But the hours of work are worth it - a highlight polish accentuates the raised details of your radiator wonderfully and creates a beautifully authentic aged look and feel.

As the name suggests, a bare metal finish is a finish in which all of the manufacturing marks such as Casting Chaplets are left visible. This finish gives radiators an industrial, yet surprisingly aesthetic look. 

It’s important to note however, that bare metal finish radiators are finished with a clear lacquer top coat. This ensures that your radiator is protected from corrosion and guarantees that your radiator will stay looking like new for years.

Cast iron radiator assembly and installation information

If you are ordering a cast iron radiator that is particularly large, then it may not fit onto the delivery pallet. For that reason, it will be delivered in two parts. To put it together you will need a joining tool (don’t worry, Trads will let you know if your radiator is going to be delivered in two parts in advance). 

Another reason that some radiators are delivered in two parts is due to weight. Large cast iron radiators can be very heavy, so providing them in smaller sections makes it easier to move them into your property and install them. 

Joining your radiator together into one piece is a straightforward job. 

A radiator will be delivered in two parts if it is over 1200mm in length. This is because it will be too large to sit on a single delivery pallet. Therefore, we have to split the radiator into two sections for delivery purposes. We will also split radiators into two parts if they weigh over 200kgs.

Assembling a two-part radiator is a straightforward job. 

Before you start, you should make sure you have an appropriate connecting tool (we will let you know if you need one when you place your order). 

Each section of radiator is held together via a threaded insert along with a reinforced expanded graphite gasket which ensures water tightness (there will be a threaded insert at the top and bottom of your radiator sections). These threaded inserts have counter-opposed threads, which means that when you tighten the insert it pulls the two sections of radiator together.

Depending on how your radiator has been delivered, there may be a set of ‘end caps’ which need to be removed before you can join your two radiator sections together. It’s important to note that these end caps have a left hand thread, so they undo in the opposite way you are likely used to. 

Once you’ve done this, you should align your two radiator sections together. You will need to put the insert in place on one section of the radiator. Thread it in slightly. It helps to place the reinforced expanded graphite gasket around half way along the inset. You then want to connect the insert to the other section of the radiator to the insert. You should be able to turn the insert using the connecting tool until the two sections are loosely connected. 

Once you’ve done that, push your connecting tool down to the point at which the two sections of the radiator join. By turning the connecting tool, you should be able to turn the insert and pull the two sections of the radiator together. Make sure you don’t fully tighten the top or bottom inserts in one go. You should tighten the top and bottom in turn, bit by bit, so that the two sections evenly come together and connect.

We sell the tools that you require on our website here. There are four different sizes to choose from (the 1 ½ inch tool being far the most popular). If you are unsure what size tool you require, we have listed the radiators that are compatible with each tool on each tool’s page.

However, when you order a Trads cast iron radiator, the Trads website will automatically select the correct size tool for you. All you will need to do is pay the cost for postage and packaging (delivery and return) and the cost of the tool will be refunded to you (please include a note in the package so that we know who is returning the tool). 

If you require any instruction or assistance in the assembly of you radiator, please refer to our 'how-to' videos here.

Measure the diameter, and then use this conversion table to determine the correct connector size.

Connector Size

Outside Diameter mm / inch

1 Inch BSP

33.25 mm / 1.390”

1-¼ Inch BSP

41.91 mm / 1.650”

1-½ Inch BSP

47.80 mm / 1.882”

2 Inch BSP

59.61 mm / 2.347”

Valve thread sizes

BSP Thread Size

Outside Diameter mm / inch

½ Inch BSP

20.99 mm / 0.825”

¾ Inch BSP

26.44 mm / 1.041”

1 Inch BSP

33.25 mm / 1.309”

½ inch threads are the most popular, with around 90% of radiators using this size valve. Whereas, 1 inch valves are only rarely used - they are typically used on much older radiators (for example radiators in period properties).

If you have a radiator that has a ¾ inch inlet at the bottom and the valve tail is ½ inch, you have two options - either get a reducer to take the ¾ inch inlet down to half inch or get a different bushing on the radiator to change the inlet to ½ inch.

Wall stays provide support for your cast iron radiator, helping to anchor it in place. How many wall stays you require will depend on the size of your radiator.

At Trads we recommend that you use one wall stay for a radiator of between 3-10 sections. For radiators of 11-20 sections you should use two wall stays, and for radiators of 20 or more sections you should use three wall stays.

Heated towel rail information

The majority of Trads' heated towel rails are designed and manufactured to be part of a central heating system.

However, many of Trads' heated towel rails are dual fuel compatible i.e. can be connected to a central heating system and also have a heating element installed to allow towels to be dried in the warmer months without the central heating being on. It’s worth noting that dual-fuel heated towel rails cannot be used with a heating element alone, and must also be connected to a central heating system.

The type of Trads heated towel you buy, will determine what sort of valve you need to buy. Each towel rail requires one valve set, so it’s important that you buy the right type.

Whilst the majority of heated towel rails have inlets that are 15mm in size, some much older central heating systems require a larger inlet size. At Trads, we can accommodate this thanks to our wide range of heated towel rail valves.

When selecting a valve for your heated towel rail, you can choose between manual towel rail valves and thermostatic towel rail valves.

As detailed above, the difference between a manual valve and a thermostatic valve is that a thermostatic valve will continually monitor the temperature of the room, adjusting the temperature of your towel rail accordingly. With a manual valve, it’s up to you to change the temperature of the radiator.

To make selecting a valve for your heated towel rail easier, we show the compatible valves for your desired towel rail at the point of order.

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