Our customer had already fitted a Hot Water & Central Heating installed Hometronic system in his main residence, complete with an accumulator boosted hot and cold water system.

He has a beautiful wooden barn building, separate from the house, which he uses to work from home.

We discussed using a combination boiler and radiators, but the sloping eaves design of the barn and the various space constraints within meant that radiators would not be ideal.

The barn, having a roof room with a vaulted ceiling, gets very warm in the summer, so we recommended fitting a heat pump.

Historically, a heat pump has two speeds, on and off, which for a heating appliance is uneconomic, because the task is never quite the same every day (British weather being what it is!).

The Worcester Bosch air/air heat pump is the latest modulating design, manufactured by Bosch subsidiary IVT.   This means it can deliver a higher level of efficiency than earlier units.

The Worcester Bosch heatpump has two components, an internal fan assisted heating /cooling unit, which is very small,

Ground floor unit

Ground floor unit


and an outside unit containing a quiet fan.  The outside fan unit extracts latent heat from the outside air, by passing very large volumes of low temperature air across a heat exchanger.

Outside Bosch air 2 air

Outside Bosch air 2 air

This low level latent heat – which can be extracted even in temperatures as low as   -12ºC – is forced through an electrically powered (variable rate) compressor and transmitted via a pair of small bore refrigerant pipes to the inside unit. 

The inside unit then gives up to 6kW of heating,

– using typically 2kW of energy you have paid for,

– and 4kW of latent heat from outside, which you have not paid for. 

In very warm weather the unit can work backwards, extracting heat from the inside unit and discharging it outside, cooling the office.

Generally speaking, electric heating is very expensive.  Conventional heaters use resistive elements (eg: night storage, electric fan heaters, immersion heaters etc) and the energy you put in, is what you get out.  So if you put in a 3kW heater, you will get 3kW of heat from it. 

The low temperature latent heat extracted from the air, once fed through the compressed and then uncompressed refrigerant, gives far more efficiency for your money.  If you put 2Kw into a Bosch air/air heatpump, you can expect to see around 6Kw output for most of the year, giving a Coefficient of Performance 0f 300%.  It sounds like an impossible ‘perpetual motion machine’, but the extra performance is coming from low temperature latent heat in the atmosphere.


Upstairs unit (grey cable is not part of our installation)

Upstairs unit (grey cable is not part of our installation)

We fitted two of these units, one to each floor.  The two compact exterior units were mounted around the rear of the building, used as a garden storage area.

Our customer reports that he is very pleased with the installation, which was fitted in January 2009.

If you have a small open plan flat, conservatory or barn conversion, and would like cheap running costs comparable or less than Natural Gas fired heating, together with air cooling in the summer, this may be what you need!