Calculating radiator sizesaigburth plumbing and heating/> Calculating radiator sizes


radiator 1

BTU (British Thermal Unit) is a measurement of the energy used in heating and air conditioning. Knowing the BTUs a unit can produce is key when heating and cooling a room. Purchasing units or room heaters that are the improper size are insufficient room heaters. Equally important when making room heating calculations is the ability to decipher the number of BTUs needed for a particular room of a particular size.




    1. 1

      Measure the room. You will need to know the square footage of the room as well as the height of the ceiling before you begin determining the BTU required for room heaters.

    2. 2

      Find the room’s volume in cubic feet. Multiply the room’s square footage by the height of the ceiling. The total is the room’s volume in cubic feet.

  1. 3

    Rate the room’s insulation. Use numbers 2, 3 or 4. Very good insulation is rated 2, average is 3, and 4 represents poor insulation.

  2. 4

    Multiply the room’s insulation rating by the room’s volume. This will give you the total number of BTUs it takes to heat a room.

If you clink on this link you can work out your btu’s and then be able to order the correct sized radiator for your room.

Radiator problems


If your radiators are cold on the top it’s more than likely they need bleeding.  You need a bleed key and a dry cloth.  At the top right hand side of the radiator you should be able to locate a nipple. Insert the bleed key into the nipple and start turning anti-clockwise.  You should start to hear air coming out.  Eventually water will start spurting out and then you turn the nipple back clockwise to shut the radiator water back off again.


Check the pressure on the boiler whilst you are doing this.  If the water pressure is at zero you need to keep topping it up to 2 bar whilst you go through the process of bleeding all your radiators.