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Posted: January 18, 2018

Heat emitters

-Heat emitters

-Patrick Wheeler


  • Radiators


The vast majority of homes in the U.K are heated by radiators, although not necessarily the most effective way to heat a home they are the most cost effective to install and most homes already have them.  They are quite simply steel or iron panels or tubes filled with water which is heated by a boiler or heat pump.  As the water cools down transferring heat via convection from the panels to the air the water returns to the heat source (boiler or similar) to be heated back up and pumped back into the system.

The radiators that were fitted in your house ten years ago are probably perfectly ok, as long as the system water hasn’t been dirty they will be pretty much as good as the day they were fitted.  If your radiators are older than that then the likelihood is they are not efficient, they might not have additional convection fins and they are almost certainly undersized.

Fifteen years ago and more radiators sizes were calculated to match the heat loss of the room as they are now but with one difference.  Older boilers used to run at far higher temperatures, modern condensing boilers are most efficient at around 50–65°c (flow temperature) but boilers in the 1970’s-1990’s ran at very high temperatures.

Because of that the radiators that were fitted 15 years ago or more are likely to be undersized by up to 40%.  Even if the radiators are in good condition there is a great benefit in installing a larger equivalent with convectors.  The lower the temperature you can run them at the less gas you will need to burn and the more the boiler will be able to condense.

2018-01-18 17.19.12

Radiator fins


  • Underfloor heating – wet


Probably the best way to heat a property, heat rises.

Underfloor heating runs at very low temperatures, ideally somewhere between 35-45°c so it is great with modern condensing boilers.  Each set of underfloor heating tubes will run to a manifold which is likely to have a thermostatic blending valve and a pump.  The manifold ensures the correct design temperature and flow is given to each circuit (flow and return) of pipes.

It is generally cheaper to run than a system of solely radiators, most of the produced heat can be used as it is heating the floor directly and heating from beneath the room.  Radiators use convection the heat up the air around them which travels up and then into the room.  Underfloor heating uses the same principal but as the pipes are in all parts of the room there is a much more even temperature.

The only big problem with underfloor heating is installing it, most properties in the U.K have wooden floors and low ceilings and although retro fit options exist they are not cheap.  We can install underfloor heating in most types of property, as long as you don’t mind the upheaval there are many retro-fit options available to go in-between the floor joists.  The floorboards can then be refitted and either carpet or another covering to finish the room as you like.

Fitting underfloor heating in new build properties is far easier, as long as it is part of the planning phase making the extra room in the floor and making sure the ceiling height won’t be affected is easy enough.

The insulation levels required by modern building regulations make most modern houses enormously thermally efficient and the low temperature and slow response of underfloor heating make it a good fit for new build.

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An underfloor heating manifold



  • Electric heating – underfloor or panel


Electric underfloor heating is far easier and cheaper to install compared to water filled tubes.  Electric cables are run with a very low profile and can be easily put underneath tiles for bathrooms within the screed.

It is, however very expensive to run.  Electricity at the time of writing this is over 20p per kw.  This makes electric heating of any kind far more expensive than a gas lead water filled heat source.  Although the initial low outlay is enticing, unless you have a free or cheap source of electricity the running costs long term will be painful.

If you have micro generation, solar photovoltaic or wind for instance and can store the electricity then electric heating becomes far more viable.  Power generated en-masse is not efficient, unfortunately even green energy from wind farms and solar loses a lot through the grid.  Small scale generation is very good because there are few leaks and it doesn’t need to travel.  This is likely the future of heating, we have the technology but we don’t yet have the incentive.

Electric panel radiators are also available, filled with a water and corrosion inhibitor or another thermal transfer fluid.  They can be installed by a qualified electrician rather than a heating installer and special consideration must be made to the draw on the supply.

Electric radiators should be only installed when cheaper emitters are not practical or cannot be used.  Building regulations for instance stipulates that for conservatories a separate heat source to the main house should be used, this could be interpreted as requiring electric heating.

Electric radiator

Electric radiator


  • Convectors

Like radiators convectors are filled with water and heated by the boiler (or other), unlike radiators which only use natural convection to heat a space they incorporate a mechanical fan to increase output.

The most common domestic convector is a kickspace heater, these are found at ground level under the kitchen cupboards and activated thermostatically when the heating is on.  They use a fan to drag air across the heated tubes and use convection fins to maximise the heat that can be transmitted from water to air.

The output of a fan convector is far greater per kg of water than a radiator so they are generally far smaller.

Myson kickspace heater

Myson kick space heater


  • Combining different emitters


It is quite common to have a mixture of underfloor heating and radiators, often systems are designed to have underfloor heating on the ground floor and radiators / towel rails from the first floor and above.  The ground floor then heats the majority of the house from the base level and the above radiators top it up to prevent the cold.

One problem with radiators and underfloor heating is the difference in design temperatures.  Radiators will need to run at 45°c and above* and underfloor heating will run from 50°c and below.  Because of this it is often recommended to fit a low loss header to allow constant temperature flow through the boiler without affecting the return temperature too greatly.

Low loss headers are common in commercial heating, more than ever they are starting to creep into domestic installations and although not a panacea are often a crucial tool to maximise the efficiency of modulating and condensing boilers.  But they definitely deserve a whole post of their own.

Low loss header

Low loss header




*this is a generalisation, they may run lower depending on external temperature, emitter size, insulation of property etc.

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