Cold room in your home? We look at BTUs

Wood burning stove in the home

Many of us have been swooning under the heat this summer as we’ve struggled to work from home. However, as the heatwave becomes a distant memory, what was once a comfortable working environment may soon feel more like the inside of the fridge. We look at one of the reasons you may have a cold room in your home.

Every room in your house has a different function, and the ideal temperature very much depends on the room’s purpose. You might want to sit for long periods in the living room or office, for example and, as such, you will want the room to be warmer than perhaps the hallway.

The ideal size of the radiators and boiler needed in your home can be determined with a few calculations. This is done by working out the British Thermal Unit (BTU). The BTU is the standard heat measurement used to represent the energy required to heat a pound of water (about one pint) by one degree Farenheit.

The BTU rating of a radiator will tell you how much heat it can emit and will help you choose the correct size of radiator for the room. In simple terms, the higher the BTU output of a radiator (or towel rail), the hotter it will get. 

The BTU of a radiator is important because it will help prevent you from making such mistakes as fitting a oversized heated towel rail in a tiny en suite or a too-small radiator in an open plan living space. A radiator that is too small will inevitably result in a cold room.

Installing a heating system that is too big will simply mean your home is too warm and less economical (although, admittedly, thermostatic radiators can help to balance the temperature). A heating system that’s too small simply won’t be capable of reaching the desired temperature.

Adding an additional radiator to a cold room on an already installed system can also create problems if the heating system isn’t big enough to cope with the additional demand.

To make sure your rooms are comfortable, you first need to ascertain the ideal temperature for each room’s purpose. Elderly and vulnerable people may prefer slightly higher temperatures, but for most people the comfortable range will be:


Ideal Temperature (deg C)





Dining Room








To estimate the ideal size for the radiator(s) in a room you need to work out the BTU output required. You can do this with a tape measure and a visual assessment of the heat loss from each room. Heat loss will depend on factors such as window sizes, type of glazing, the number of doors and the construction material used to build the property.

If this is already getting too much for you, ask a heating expert for help. Alternatively, for a quick and easy ‘rough guide’ method, there are a number of BTU calculators available through a Google search with a few simple calculations:

  1. Multiply the height, width and length of the room to calculate the volume in cubic metres.
  2. Count the number of windows and external doors.
  3. Ascertain whether the room is north or south facing.
  4. Now input this information into your chosen BTU calculator.

When selecting a radiator, choose the next size up from the one required if you aren’t lucky enough to find one the perfect size.

To calculate the ideal size of the boiler you need, add together all the BTUs for each of the rooms in the whole house.  If you have a hot water tank, add another 20% and then another 10% to achieve the final total.

This won’t give you a perfect answer, but it will help to keep you warm without the additional bills.