Through the wall twin duct units, are all in one systems, they have no outdoor units and therefore no pipe connections, this makes them very DIY friendly. All that is visible on the outside are 2 discreet grills for air on and air off.
At only 465mm high the 2 smaller models Fit on nearly all dwarf walls making them perfect for conservatories. In addtion to this, having no outdoor unit means they are ideal for apartments and hotels, they can be nearly always installed entirely from inside. They are also suitable for listed buildings and areas where planning permsision would be necessary if an outdoor unit was used.
They are also popular for portacabins and portable offices.
NB - Compared with split systems efficiency is poor with a heating efficiency ratio of 2.5kw produced per kw used.