Does it matter which side of radiator flows & returns?

Does it matter which side of radiator flows & returns?


If you’re having a go at installing a radiator yourself, then you are probably aware that one side of the radiator allows the hot water to flow into the radiator, while the other side returns the colder water back to the boiler. Knowing which is which is important, so in this article, we’ll explain the differences and how you can make sure your radiator installation goes smoothly.

What are flow and return pipes?

In a central heating system, the flow and return pipes are a crucial component of the plumbing system. The flow pipe carries hot water from the heating system's boiler to the radiators, while the return pipe carries cooled water back to the boiler.

The flow pipe is typically connected to the outlet of the boiler, and the hot water flows through it to the radiators. As the hot water passes through the radiators, heat is transferred from the water to the air in the room, warming the room. The cooled water then flows back to the boiler through the return pipe, where it is re-heated and circulated back through the system.

The flow and return pipes must be properly sized and installed to ensure efficient and effective heating. Improper sizing or installation can result in issues such as low water flow, poor heating performance, or even system failure. It is important to consult a professional for proper installation and maintenance of a central heating system.

Typically, the side of the radiator marked as "inlet" or "supply" is intended to be connected to the hot water flow from the heating system's pump, while the side marked as "outlet" or "return" is intended to be connected to the return line that carries cooled water back to the heating system's pump. However, in some cases, it may not matter which side is used for the flow and which side is used for the return, as long as the connections are made properly.

What's the easiest way to identify the flow pipe?

The most straightforward way to identify the flow pipe in a central heating system is to follow the flow direction. The flow pipe carries hot water from the heating system's boiler to the radiators, so it should run from the boiler towards the radiators.

You can use the following steps to identify the flow pipe:

  1. Locate the boiler: Find the location of the boiler in your heating system.
  2. Look for flow direction indicators: Some heating systems have arrows or labels indicating the flow direction. If your system has these, follow the arrows or labels towards the radiators to find the flow pipe.
  3. Observe the pipes: If there are no flow direction indicators, observe the pipes. The flow pipe should be hot to the touch, as it carries hot water.
  4. Confirm with a flow meter: If you are still unsure which pipe is the flow pipe, you can use a flow meter to confirm (if you're a professional). The flow meter will indicate the direction of the flow and help you identify the flow pipe.

How to ensure radiator valves are installed on the right pipes

To ensure that radiator valves are installed correctly on the flow and return pipes, you should follow these steps:

  1. Determine the direction of flow: Before installing the valves, it is important to determine the direction of flow in the piping system, which you can do by following the steps outlined above
  2. Identify the flow and return pipes: Once the flow direction is established, you can identify the flow and return pipes. The flow pipe carries hot water to the radiator, while the return pipe carries cooled water back to the heating system.
  3. Install the valve on the flow pipe: The radiator valve should be installed on the flow pipe, near the radiator. The valve should be installed in the upright position with the flow direction facing towards the radiator.
  4. Connect the valve to the radiator: Connect the radiator to the valve using a flexible hose or compression fitting. Ensure that the connection is tight and secure to prevent leaks.
  5. Install the valve on the return pipe: The radiator valve should be installed on the return pipe, near the radiator. The valve should be installed in the upright position with the flow direction facing away from the radiator.
  6. Connect the radiator to the return pipe: Connect the radiator to the return pipe using a flexible hose or compression fitting. Ensure that the connection is tight and secure to prevent leaks.
  7. Test the system: Once the valves are installed, turn on the heating system and check for leaks. If everything is working properly, you should be able to adjust the temperature of each radiator by turning the valves.

Should thermostatic radiator valves go on the flow or return?

A thermostatic radiator valve (TRV) is typically installed on the flow pipe of a central heating system. The TRV regulates the flow of hot water to the radiator based on the room temperature, allowing you to control the temperature of each individual room.

When installed on the flow pipe, the TRV senses the temperature of the room and adjusts the flow of hot water to the radiator to maintain the desired temperature. If the room is too cold, the TRV opens to allow more hot water to flow through the radiator, warming the room. If the room is too warm, the TRV closes to reduce the flow of hot water, cooling the room.

Quality radiators at Trade Radiators

At Trade Radiators, we have a massive range of well-priced, energy-efficient and easy-to-install radiators.

With the best range of radiators you’ll find from any UK store, better delivery and our unique price promise, we aim to help any room across the country get the radiator it deserves. It all starts with knowing what you need from a new radiator.

Browse our extensive range of quality radiators by criteria that matters to you most. Whether you’re looking for a particular style of radiator, such as column or designer, or a special colour to suit your home’s interior, Trade Radiators has something perfect for your requirements.



Thermostatic radiator valves at Trade Radiators

A thermostatic radiator valve allows you to adjust the temperature of your radiator with just a simple turn of the dial. The easy-to-read numbers will accurately keep track of how much heat your radiator is putting out and helps you to use your heating more efficiently. For example, you can have the central heating running in your home, but not in your second bedroom which is rarely used. TRVs enable you to only warm up the areas in need of heat, without unnecessary waste.

Many people are making the switch from traditional manual valves to something which can afford the user a bit more versatility and control when heating any space. Take a look at the current range of thermostatic valves currently in stock at Trade Radiators, with some fantastic items available.


Related Posts
How to hide vertical radiator pipes

How to hide vertical radiator pipes

Many people find exposed radiator pipes unsightly, but it's not always possible to hide them under the floor or in a wall. This article goes through some alternative ways to hide or disguise your vertical radiator's pipework.

VIDEO - Learn how to pipe a radiator

VIDEO - Learn how to pipe a radiator

In this post, we look at how you can learn to pipe a radiator. This may be something you need to do with new radiators, so have a look at doing this with James the plumber. 

What are the different types of pipework installations used in central heating systems?

How does the pipework in your central heating system operate and what are the pros and cons of the different pipework installations?

VIDEO - How to install a column radiator

VIDEO - How to install a column radiator

James the plumber is back with a very detailed and educational video on how to fit a column radiator! Visit our website today to read more or browse through our column radiator range.

VIDEO - How to install a heated towel rail

VIDEO - How to install a heated towel rail

James the plumber takes you through the process of installing a curved chrome heated towel rail into one of the bathrooms of a Trade Radiators customer. See if it inspired you to have a go!

Related posts
How to hide vertical radiator pipes
17 January 2023

How to hide vertical radiator pipes

Many people find exposed radiator pipes unsightly, but it's not always possible to hide them under the floor or in a wall. This article goes through some alternative ways to hide or disguise your vertical radiator's pipework.

How to stop your heating pipes from making noises
VIDEO - Learn how to pipe a radiator
30 June 2015

VIDEO - Learn how to pipe a radiator

In this post, we look at how you can learn to pipe a radiator. This may be something you need to do with new radiators, so have a look at doing this with James the plumber. 

2 December 2014

What are the different types of pipework installations used in central heating systems?

How does the pipework in your central heating system operate and what are the pros and cons of the different pipework installations?

VIDEO - How to install a column radiator
7 August 2014

VIDEO - How to install a column radiator

James the plumber is back with a very detailed and educational video on how to fit a column radiator! Visit our website today to read more or browse through our column radiator range.

VIDEO - How to install a heated towel rail
1 November 2013

VIDEO - How to install a heated towel rail

James the plumber takes you through the process of installing a curved chrome heated towel rail into one of the bathrooms of a Trade Radiators customer. See if it inspired you to have a go!

Chat with us on WhatsApp