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How to check radiator efficiency

person checking for radiator - Radiator Efficiency

Radiators are a big deal here in the UK. They can mean the difference between a cosy, warm winter and a miserable one. So, whether you’re a homeowner or a landlord, this guide will help you get the most out of your central heating system by identifying the most efficient radiators for your property, which involves knowing the best size and type for your particular space.

Maintenance is key to keeping your radiators efficient, so our HomeServe home experts have included a guide to diagnosing issues with your radiators, along with flushing and bleeding them. Get to the end of this article and you’ll be your very own rad expert, so let’s talk radiator efficiency!

Table of contents

  1. How efficient are my radiators?
  2. How to make sure your radiators are working efficiently?
  3. What size radiator do I need?
  4. What is a BTU?
  5. FAQs

How efficient are my radiators?

Well, there’s a simple process of elimination you can work through to find this out. Eliminate the following issues and you’ll be dealing with your current radiators at their maximum efficiency:

Cold spots

The first problem you should eliminate is cold spots in your radiators, which can be caused by air bubbles trapped in amongst the water. The cold spots in this case are usually at the top of the radiator. In this case, cold spots are typically found at the top of the radiator and can be easily removed with bleeding a radiator.

How to bleed a radiator

You should bleed your radiators if you notice cold spots at the top of the radiators – which is essentially letting out the trapped air by using a radiator key. It can be a messy job so follow our step-by-step guide to How to bleed a radiator for detailed information.

Signs that you need a powerflush:

If you have cold spots at the bottom of your radiator, it’s probably a sign that you have a build-up of sludge, corrosion and debris in your central heating system. This is a bigger issue that will require you to perform a suitable system cleanse on your system. Here are some other symptoms that you may be experiencing:

  • Cold spots on your radiators, particularly at the bottom
  • The radiators require constant bleeding
  • Noisy radiators and boiler
  • Radiator leaks
  • Frequent breakdowns
  • Boiler constantly needs to be restarted
  • Central heating takes a long time to heat up
  • Some radiators struggle to heat up more than others
  • Discoloured water when radiators are bled
  • Cold radiators but hot pipes

In this case, it’s time for a suitable system cleanse. Go straight to our guide on how to perform a powerflush on your central heating system, follow it step-by-step, and then you will get your radiators working at their maximum efficiency.

How to make sure your radiators are working efficiently?

Do you have air in your radiator?

An easy way to check if your radiators have any air in, is to place your hand on or near the radiator (warning: be careful and don’t burn yourself if the radiator is hot) and check for any cold spots.

Before you do this, allow the heating system to obtain maximum temperature and ensure that thermostats etc, won’t operate and shut the radiator off ahead of time. If you feel a difference in temperatures at the top of the radiator you will need to consider bleeding your radiator to allow any air to escape.

To do this, turn off the central heating system, place a radiator key or small screwdriver into the radiator bleeding valve, turn the valve to the left to open the valve. You will hear air rushing out. For best practise, place a cloth or rag over the valve to stop water rushing out which will help prevent spilling. When water starts to pour out of the bleed valve, you will then know that all air is out of that one radiator.

Should I replace my radiators?

If you’ve bled and powerflushed your current radiators and their maximum efficiency isn’t blowing you away – or if you’re renovating your house and looking for a wholesale upgrade to your central heating system and radiators, then let’s talk about what to look for in a new set of radiators.

Plumbed or electric?

Have you considered that perhaps gas central heating isn’t your only option? You might associate electric radiators with the 1970’s but they’re actually becoming a trendy alternative for heating homes because of the advances made in electric heating over recent years.

100% electric efficiency

Did you know that gas boilers aren’t 100% efficient? Even brand new boilers are only able to be about 90% efficient, whereas electric radiators will turn 1 kWh of electricity into 1 unit of heat, meaning they are 100% efficient.

No wasted heat

Electric radiators heat only the room that they’re in, whereas a central heating system has to pump hot water through the pipes in the walls of the house to get to the room or rooms that you really want to be warm. This means a certain amount of all that thermal energy is inevitably wasted.

Great for bathrooms and home offices

It’s for this reason that electric radiators are perfect for rooms that need to be warm when you don’t necessarily need the rest of your central heating to be on like bathrooms and your work-from-home office.

Greater running costs

Pound for pound – or radiator for radiator – one electric radiator costs more to run than one central heating radiator. But when you factor in how you use heating in your home – and how much is wasted – it may work out as cheaper overall to have an electric radiator in a certain room of your home.

Should I buy aluminium radiators?

Did you know that you can get radiators made out of different materials? Alongside steel and cast iron you can even get natural stone radiators. However, aluminium radiators are the most efficient radiators you can get these days for many reasons:

It’s an excellent heat conductor

Aluminium is very good at conducting heat, which means it can quickly heat up to the room temperature you want, so 15% less energy is used compared with other radiator metals.

This means if you’re looking for new radiators for your home or property, you can potentially save as much as 15% in terms of energy (and your heating bills). Over the course of a few years this adds up to a lot of energy and money saved.

It’s recycled and recyclable

Most aluminium radiators are made using recycled aluminium, and at the end of their lives the aluminium can be reused, which is also very environmentally friendly.

What size radiator do I need?

It’s important to get the size of your new radiator right in relation to the size of the room you want to heat. The size of the radiator directly correlates to how much heat it will give you. A central heating radiator’s heat output is measured in kW, which stands for KiloWatts.

What is a BTU?

BTU (British Thermal Unit) is the measurement of a kW that represents how much energy it takes to heat 1 pound of water by 1 degree centigrade.

All gas central heating radiators come with akW rating, which tells you how many BTUs (how much heat) it generates. It’s a good way to compare radiators you like the look of.

The best way to work out how much heat you’ll need is to:

1. Measure the dimensions of the room you want to heat

2. Use an online kW calculator to add your measurements and other factors like double glazing

3. The result will give you a kW requirement for the room

If you’re struggling to match the exact kW rating you need with a radiator, choose one with a slightly higher output to make sure your room is warm enough but don’t go overboard with the size of the radiator as the pipework feeding it may also need to be upgraded to carry the extra heating load.

If you’re sold on the efficiency gains of electric radiators, you can also convert your kW requirement into watts so that you can shop for the most suitable electric radiator for your chosen room.

Happy radiator hunting!

If you’re in the middle of a renovation and need a new boiler to go with your new radiators, we’re working with BOXT, one of the largest boiler installation companies in the UK, who provide a second-to-none boiler installation service. Get your fixed price quote here.


Is a radiator 100% efficient?

A gas central heating radiator system can never be 100% efficient because the whole system uses pipes to pump the hot water around your home. Even brand new boilers are only able to be about 92% efficient, whereas electric radiators will turn 1 kWh of electricity into 1 unit of heat, making them 100% efficient.

Are old radiators less efficient than new ones?

You can lengthen the lifespan of your radiators by ensuring that the levels of inhibitor within the heating system is sufficient to provide ongoing protection to the system and prevent the onset of corrosion, this should be checked every 12 months by a heating professional.

Which are the most efficient radiators?

Aluminium radiators are up to 15% more energy efficient than cast iron or steel radiators, because aluminium heats up more quickly, and the radiators might use less water.

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