Heat Emitters

You can use conventional radiators and towel rails, low temperature fan assisted radiators, fan coils and under floor heating with a heat pump system.

A heat pump loses efficiency with higher water temperatures. Therefore we need to try to keep the water temperature as low as possible.. But the lower the water temperature the smaller the output from the heat emitters.

A heat pump can produce water at up to 55 degrees (or 65 degrees with a Panasonic HT system and even hotter with a Daikin cascade HT system) but will not qualify for the RHI at these hotter temperatures. For this reason we show ratings on this page and on the Aquarea selection page assuming -

  • Standard Radiators water flow at 50C & return at 45C and air at 20C so 27.5C TD
  • Low temperature radiators at 45C flow, 40C return and 20C air so 22.5C TD
  • Under Floor heating at 35C flow, 30C return and 20C air so 12.5C TD

This TD figure is important because conventional radiators are rated by their manufacturer at 50C TD (75C flow, 65C return and 20C air) and there is a conversion factor for conditions other than these. This is not just important for heat pumps but also condensing boiler systems that require the return water temperature to be around 50C to operate correctly. Typically a condensing boiler system will operate with flow 60C, return 50C, air 20C so TD of 35C.

According to Stelrad the conversion factors for these different conditions would be

  • Conventional boiler 50C TD - 100%
  • Condensing Boiler 35C TD - 63%
  • Standard Radiators 27.5C TD - 46%
  • LT Radiators 22.5C TD - 35%
  • UFH heating 12.5C TD - 17%

Conventional Radiators

If you are using a conventional radiator then you can calculate the output with a heat pump using the manufacturers rated capacity and apply the correction factor as discussed above


The depth of these is 78mm for a P1, 94mm for a K1, 112mm for a P+ and 135mm for a K2

Figures for a 450mm high 1000mm wide Stelrad Compact

 Model Rated TD50C Cond Boiler TD35CStd Rads TD27.5C LT Rads TD22.5C 
 P1 0.47KW 0.30KW0.22KW 0.16KW 
 K1 0.76KW 0.48KW0.35KW 0.27KW 
 P+ 1.06KW 0.67KW0.49KW 0.37KW 
 K2 1.37KW 0.86KW0.63KW 0.48KW 

Figures for a 600mm high 1000mm wide Stelrad Compact

 Model Rated TD50C Cond Boiler TD35CStd Rads TD27.5C LT Rads TD22.5C 
 P1 0.62KW 0.39KW0.29KW 0.22KW 
 K1 0.98KW 0.62KW0.45KW 0.34KW 
 P+ 1.73KW 1.09KW0.80KW 0.61KW 
 K2 2.39KW 1.51KW1.10KW 0.84KW 

Obviously for radiators slimmer than or wider than 1m can be calculated by multiplying the above figures by their actual size in metres in order to get an approximate capacity.

Panasonic Aquarea Air low temperature fan coils

More details here. These are hybrid radiators and fan coils and are capable of cooling and heating as standard.

There are three models all of which are 659mm high and 129mm deep. It is only the width that changes with the AIR200 at 735mm, the AIR700 at 935mm and the AIR900 at 1135mm.

Figures for the AIR models at various different fan speeds and water conditions are shown on the main AIR page here but below is a similar chart to the one for the conventional radiators at high fan speed.

 Model Rated TD50C Cond Boiler TD35CStd Rads TD27.5C LT Rads TD22.5C 
 AIR200 2.24KW 1.56KW1.22KW 1.00KW 
 AIR700 4.61KW 3.21KW2.51KW 2.05KW 
 AIR900 6.44KW 4.50KW3.52KW 2.87KW 

It is obvious from this chart that size for size they significantly outperform a conventional radiator.

Jaga Strada Low temperature radiators

We are big fans of the Jaga Strada low temperature radiators which are significantly quieter than a fan coil and perform very well. They are suitable for installation with a TRV mounted internally and come in a variety of different case sizes.

Jaga Strada 650mm high 1000mm wide models

 Model Rated TD50C Cond Boiler TD35CStd Rads TD27.5C LT Rads TD22.5C 
Type 06 1.34KW 0.94KW0.74KW 0.60KW 
Type 11 2.14KW 1.50KW1.18KW 0.96KW 
Type 16 3.13KW 2.19KW1.72KW 1.41KW 
Type 21 3.99KW 2.79KW 2.20KW 1.80KW

Type 06 is 85mm deep, Type 11 is 118mm deep, Type 16 is 168mm deep and Type 21 is 218mm deep.

Please contact us for a selection for your application.

Oh - in the photograph above where the radiator is shown next to the bed, that is not a posed publicity shot - it is a live example and the house owners sleep right next to it, showing how quiet the Strada models really are!

The Strada is not the only design available but it is the biggest seller. Two very attractive options are shown below.

Under Floor Heating

We do not offer an Under Floor Heating product ourselves but these are widely available. Ask your supplier to design based upon 35C flow and 30C return suitable for a heat pump.