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Heat Loss BTU Calculator

Calculate heat loss per room of your home to choose the right size and style radiators.

We offer basic and advanced heat loss programmes that will help you calculate the BTU (British Thermal Unit) requirement needed to heat your room or project. Discover more about our BTU calculator here and information on why this is a crucial step before buying radiators.

Both the basic and advanced heat loss calculator programmes are online platforms, meaning you can quickly use them whenever needed. For the advanced programme, you will need to log in which can be done from anywhere to access your account. Doing so will give you access to all of your previous projects that are stored and can be easily duplicated, saving you time and hassle.

All you will need is a few details about your home to get started with calculating BTU for a room. Calculating BTU for radiators is an essential step to ensure the room where you are installing radiators will be sufficiently heated. As a basic rule of thumb, the larger the room, the bigger the radiator or number of radiators required, whereas a smaller room will need a more compact radiator.

However, to ensure as much accuracy as possible before purchasing, calculating BTU for radiators is the best way to ensure heating efficiency throughout your home. If you’ve never considered this before, or you are buying radiators for the first time, we are here to help.

Basic Heat Loss Programme

Using our heat loss calculator will provide you with a quick estimate of how much heat you need for your room or project.

The Stelrad basic heat loss calculator makes various assumptions based on your choices and may not consider all factors relating to your particular requirements. If you require a more detailed calculation, please use the advanced version of the programme at starsapp.co.uk.

We accept no liability for any errors resulting from the estimates given using our BTU calculator. All calculations are based on Delta-T 50°C (Δ-T50°C) in accordance with BS EN 442. Your use of the Stelrad basic heat loss calculator is subject to these terms and conditions.

STARS – Advanced Heat Loss Programme

Our advanced heat loss programme is also known as STARS (Stelrad’s Technically Advanced Radiator System).

Use this heat loss programme for a comprehensive calculation which allows you to enter all the parameters that affect heat loss in your room.

A step up from the basic BTU calculator, STARS is an online heat loss programme designed by us for anyone who needs to calculate heat loss for a room or needs a radiator size calculator. This will give you more comprehensive results for the heating requirements that you need to know for a project.

The advanced heat loss calculator programme takes the user through a simple step-by-step process of inputting key information for any room type including the wall, floor and ceiling dimensions, choosing wall materials and door and window types. This enables instantaneous heat loss calculations using the unique room planner where you can simply drag the walls and calculate the output figure in real-time.

Once the room specification is completed the heat loss programme suggests a selection of appropriate radiators from our product portfolio. A radiator can then be selected to replace heat lost in the room. STARS will also calculate the heating requirements for an entire building and suggest appropriate boilers (combi or heat only). A radiator schedule and boiler specification can then be printed or saved for your reference.

BTU Calculator – Other important terms

You will find additional terms and conditions and assumptions within the STARS app.

We may update, vary, and amend these assumptions and terms from time to time without prior notice. Each time you use the BTU calculator programmes, the assumptions used at that time will apply.

Please click here to find out more about the advanced heat loss programme.

How to Calculate BTU for a Room

If you want to know how to calculate BTU for a room, consider the following:

  • Measure the length, width, and height of the room in meters using a tape measure. Multiply the three dimensions to find the cubic meters of the room.
  • Use a BTU calculator or the following formula to calculate the BTU required to heat the room: BTU = (cubic meters of the room) x (insulation level factor) x (temperature difference factor). The temperature difference factor is calculated by subtracting the outside temperature from the desired temperature. The insulation factor is how well insulated the room is, rated good to poor.
  • Once you have calculated the required BTU, select a radiator with a BTU rating that matches or exceeds this value.
  • Other factors to consider when selecting a radiator include the style, size, and material.

Using our BTU calculator helps you define the BTU for a room and choose suitable radiators all in one easy-to-use tool. This is much simpler than working out the calculation yourself and will provide the accuracy you need to decide on which radiator.

How to Work Out BTU for a Radiator

Working out the BTU for a radiator can be complex. The amount of BTU a radiator has will tell you how well it will heat a room. The higher the BTU output, the more powerful the radiator is. However, before you choose the most powerful radiator, you’ll need to consider other features of the room as it’s not just about the radiator size.

This makes BTU a very useful thermal measurement. It helps you consider other factors of the room such as the level of heat loss. For example, the room size, the type of windows and walls, the amount of insulation, and any external doors will all contribute to the amount of heat loss. It will also consider what temperature you ideally want to keep your room at, as not all rooms you will want to keep the same temperature throughout the day.

Using a BTU calculator is by far the easiest way to work this out and will quickly show you the best radiators to choose from for each room.

Heat Loss Calculator for radiators
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How Many BTU to Heat a Room?

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The answer to how many BTU to heat a room will depend on which room and its features. As mentioned above, everything from the types of windows the rooms have, if any, to the amount of insulation and room size will have an impact on this. As a guide, 1 watt of energy is equivalent to 3.41 BTUs. The simplest way to work out how many BTU your room needs to be heated efficiently is to use our BTU calculator which will ask you step-by-step details about the room and will then recommend which radiators you need.

What’s the Best Setting for Central Heating?

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The best setting for your central heating will depend on how comfortable you want the room temperature to be. According to the Energy Saving Trust, this is typically between 18°C and 21°C[1].

You should ideally set your thermostat to the lowest comfortable temperature. This way, the rooms of your home, assuming you have the right radiators in each room, will stay at a comfortable setting throughout the day.

[1] https://energysavingtrust.org.uk/take-control-your-heating-home/