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How radiators heat your home

March 8, 2012

Theodd thing with radiators is that they are actually somewhat misnamed. Most ofthe heat which comes from them is actually by convection. Most modern radiatorshave fins on the back, or between its panels if it is a double (like thepicture below), as against the older style radiators that were just a panel.This has allowed smaller radiators to be used as the fins vastly increase thesurface area available for giving off heat.

Radiators work by heating the air which flows past them. Warm air rises fromthe radiators and colder air in the room falls. This circulation develops aflow of air around the room sending warm air from the radiator and deliveringcooler air back to be heated. For radiators to work well there must be adequateclearance around them so that air flow isn’t restricted. Ideally you want aminimum of 100mm clearance at the bottom, 40mm at the rear and at least 50mm atthe top. In a perfect situation the radiator would not have any obstructionabove it. Now you know why radiators are mounted off the wall a little andabove the floor.


Thesize of radiator required for a room depends upon two factors. Firstly thetemperature that you want it to be able to maintain. That is a relativelystraightforward task, but you can use this table as a guide

in degrees C

Dining Room
Secondly,the heat loss from your room. The calculations for this are actually quitecomplex since they depend upon the size of windows, number of doors and, inparticular, the construction materials used to build the house. Consult a localheating engineer if you need to fit radiators in a previously unheated room ora new extension. To give you a guide please see the calculations below. This isnot 100% accurate, it will probably oversize the radiator slightly but it willgive you an idea of the output you require to heat your room.

If you are replacing an old radiator, make a note of its details and replacewith one of similar heat output capability.

Find the volume of the room in cubicmeters (length x width x height) 

Use of Room
Lounges and diningrooms multiply by 50.
Bedrooms multiply by 40.<
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