How To Determine Radiator Size?

How To Determine Radiator Size

In this guide, I will explain how to determine radiator size so that you can buy the right type of radiator for your needs.

The UK uses a heating system called ‘radiators’. Radiators are pipes that are filled with hot water, and the heat is transferred to the room through convection. They work best in areas where there is low air movement (high ceilings, windows closed). A radiator is a device for heating water by the process of convection, so you need to know how many gallons of water your space requires per hour.

To reduce the risk of a hot water tank bursting and causing serious damage to your home, it’s important to know how much radiator space you’ll need. This article will help you figure out what size of radiator is right for your house.

The information needed to determine the size of a radiator is pretty straightforward. The first thing you need to do is measure the width, depth, and height of your space where you plan on installing this heating system.

After you have done that, go ahead and look for radiators with those dimensions online or at your local hardware store. If you are unsure about which one will work best for what type of space and how to determine radiator size, then consult our handy guide below!

How to determine radiator size

The size of the radiator needed for your home depends on many factors including: –

Type of home you live in (detached house or apartment)

One of the most important factor that determines the correct radiator size is the type of home you live in.

If you live in an apartment, then you need to take into consideration your neighbours heating system and how it might affect your rooms temperature; also if there are any external factors that affect it (external walls, wind).

Detached homes become extremely hot during summer (and extremely cold during winter). Therefore, the correct size of radiator is needed to keep your home warm in winter and cool in summer.

To determine the right sized radiator for your detached house, you need to measure the length and width of all your rooms (length x width), take an average of this figure. For an apartment, you need to check your room sizes.

Number of rooms in your home and how they are laid out (open plan or not)

Another important factor that determines the size of radiator you need for your home is how the rooms are laid out.

For example if you have a large room which contains the living area, kitchen and dining area next to each other, then there will be no problems with too much heat affecting other areas. This is because these three areas won’t affect another.

However, if your home is laid out in a different way that may cause problems with the heat. For example, if you have two rooms which are smaller than the living room and are contained within it (i.e. one room contains the master bedroom and the other contains an en suite), then this would cause a problem because the heat from the living room would affect both rooms.

The appropriate sized radiator will need to be fitted in these two rooms, and this is where problems may arise.

Home heating is a significant cost for most UK home owners, and one of the easiest ways to reduce this cost is by not heating your home when it doesn’t need to be. Therefore you should determine whether your family uses the heating system in specific time slots (i.e. during certain hours in the day).

If your home is empty for certain hours in the day, then the radiator size should be reduced because you are not using hot water/heating during this time.

Where you want to heat up first (kitchen, living room, bedrooms)

The size of the radiator also depends upon where you want to heat up first. There are certain rooms that are more important than others, especially the Kitchen. Therefore for this room, you should use a larger radiator compared to other rooms in your home.

How much power you have available from your boiler/heating system

The size of the radiator also depends on how much power you have available from your boiler or heating system.

If your boiler is more powerful, then you need to make sure you buy a larger radiator. The opposite of this situation will result in an incorrect sized radiator which may lead to needing multiple radiators fitted into each room – this would be less energy efficient and can cost more money.

How To Determine Radiator Size

How it affects your water bills

The size of the radiator you buy will also affect your water bills.

If you use less power to heat up your home, then this will save you money on your water bills because the boiler/radiators won’t need to work as hard to reach the desired temperature. However if you install a larger radiator which requires more power than needed, then this will increase your water bills unnecessarily.

If you have a radiator that is roughly half the size of its equivalent, then this can have a very noticeable impact on your energy bills and therefore it is not recommended to do so.

It will also depend on where you install the radiator. If you put it in a corner, the heat will only spread to both sides of the wall it is against. A radiator can also be installed above head height with an air gap behind it. This means that warm air stays trapped between ceiling and wall, spreading out more evenly around the room.

To determine your radiator size, you will need to calculate the total heat loss from your home. You can do this by measuring the temperature difference between inside and outside your home on a cold winter night, then add on any extra heat that is needed for cooking or drying clothes.

Radiators are available in different lengths, shapes and colours. The most common type of radiator is the close (or standard) radiator. This is the most widely used type of radiator and gives off heat quickly. The larger your room size, the more power you will need from your boiler/heating system to run it.

The average sized radiator size

There are different types of radiators which have their own specifications, but they can be categorized into two main categories: enclosed and semi-enclosed.

The average sized radiator that you need is one which has a heat output of 1000watts, although the smallest size is 500watts. If your home is relatively small, then this size will suit you fine; if your home is quite large (over 2000 square feet), then it might be advisable to use two radiators of the average size, one in the living room and another in the master bedroom.

For a larger home or an open plan house, then you should use two of these type of radiators fitted in each room (not necessarily in full view).

You might want to ask a plumber about the right sized radiator for your home. If it is not possible to speak with them, then you can follow the guidelines given below.

If there are rooms in your home that are bigger than 20 square meters, then you should fit two average sized radiators to keep these rooms warm.

The heating system should be able to produce 1500 watts of heat every hour – the electrical supply must support this general load. For a smaller home (less than 2000 square feet), a single radiator of average size should suffice. But if you have a larger home, then you might want to use two of these radiators in the most important rooms, such as living room and bedrooms.


There are different factors which determine the radiator size but the most important thing to take into consideration is the total heat loss from your home. You can get a rough estimate of this by measuring the outside temperature on a cold day and adding this number to the amount of heat necessary for cooking, drying clothes etc. A general rule would be that you should have at least one radiator per room if it is more than 20 square meters. This will allow for your home to be heated evenly and prevent hot spots, which could lead to health problems caused by the exposure of extreme heat.

Read more about how you can save money on your energy bills: “How To Lower Gas Bill In Winter“.

References : How to Size Radiators for Rooms


I am John Oakley. I love to share tips and reviews on products to keep our homes warm and comfortable.

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