Solar Space Heating System

Attic Heat Harvesting systems
The solar heat harvester system will very efficiently transfer hot solar heated air from high in your attic via insulated ducting to your home.

Before you order and install a Solar Heat Harvester System there are things you should consider:

If you wish to reduce home heating costs the first and most cost effective thing you can do is ensure that your attic floor has at least 300mm of insulation.

The area you would initially like to heat - the Attic Heat Harvester hot air outlet in your home is generally located in the lowest frequently occupied room in your home, it is better to heat a room at a low level because hot air rises tod heat all your home.

The Attic Heat Harvester controller (and the room temperature sensor) should generally be located in this room approximately 1.5m from the floor so the controller features can be easily accessed. It will be easier if the controller is located near a suitable 230vac electrical supply, from for example a 13 amp socket. The controller internal connectors on the right side of the printed circuit board will be connected via cables to the attic Fan/Blower J8, the air valve J8, and to the attic J5, and room temperature J6 sensor cables.

attic heat harvesting system circuit board

The hot air outlet vent should be fitted between 2 ceiling joists, with an air valve mounted immediately above. The air valve is automatically closed when the attic Heat Harvester is not operating stopping hot room air escaping into the attic.

Which is the hottest side of your attic - this is often the direction of the sun around 1pm. The open attic end of the flexible duct should be close to this point and approximately 300-600mm (1 to 2 ft) below the attic apex where the attic air is hottest. The attic temperature cable sensor end should be fitted close to the open end of the duct. The Attic Heat Harvester system components diagram shows the cables.

Attic Heat Harvester Mk1 Controller

attic heat harvester wiring diagram

For the system to operate well the heated air needs to be able to move from the heated room into other areas of your home, in older homes it can often escape through gaps around doors and windows.

However if your home is fairly air tight you may need to install a second air valve in the attic floor of a cool room of your home to permit are to move back into the attic to be reheated and recirculated. You may also wish to install gravity closing air vents in the heated room walls or you hallway to let the air escape to adjacent rooms.

If your home is not a single storey you will also need to decide the route the 203 or 254 or 305 mm insulated duct is going to take to pass through the upper storeys, through for example cupboards. Holes will be required in the floors in the upper storeys to pass the duct through.

Answers to the above questions will probably determine the best route that the insulated flexible duct will take. The duct length should ideally be minimized, and it’s path be as straight as possible, gentle bends are OK, but sharp bends will reduce the airflow which impairs the system efficiency.

In order to get the best solution to the steps above you may have to compromise somewhat.

When you have decided on the location of the system components you can determine the minimum length of the cables you will require, you will need these to choose the cable lengths to order.

We usually do not supply all the items your need for your system as you can easily obtain them at a lower cost and also obtain items that suit your home's decor.

The items we usually do not supply are:

a)   the insulated ducting

b)   the hose or jubilee clips that secure the ducting to the fan and one way air valve

c)   The system fused ON OFF switch and mounting box

d)   a short length of twin and earth 1mm² cable from the main supply to the fused On Off switch

e)   a short length of twin and earth 1mm² cable from the ON OFF switch to the Attic Heat Harvester Controller

f)   the air vents

g)   sundry screws and parts

At this point you can place your order.

Installation Instructions for a One Floor Home

1.   A hole is needed in the attic floor large enough to pass the insulated ducting through. Before cutting the hole ensure that there are no cables or pipes in the area and that there is sufficient height above the hole. For single storey homes generally at least 1m and preferably more is required for the air valve and the ducting bend.

2.   Make a support for the air valve from for example a piece of plywood. Cut a hole in it for the air valve you are using and fix the air valve to the support then fix the air valve support onto the floor joists. Air valves can be obtained that are 203 or 254 or 305 mm in diameter. Solar Heat Harvester Ltd stock some air valves.

3.   Connect the air valve cable to the air valve and run the cable back to the back of the controller location. The air valve power cable should be rated for at least 1 amp.

4.   Make a mounting plate for the fan/blower and fit it high in the attic ideally within 300 to 500mm from the roof apex on the most sunny side of the attic.

5.   The ducting goes from the top of the air valve to the fan unit, determine the length of ducting that you need and order it.

6.   When you have the ducting fit ducting supports as necessary to the roof trusses using wide webbing loops. Minimize bends in the ducting as bends impair air flow and reduce the system efficiency. Long straight duct lengths to the fan can be supported by a narrow piece of wood beneath the ducting, supported by wide webbing. Gentle duct bends can be made using flexible wood or plastic duct supports.

Low Attic Heat Harvester 50mm fan and support duct

7.   Securely mount the attic temperature sensor cable so that the sensor is near the centre of the open attic duct end, and run the sensor cable together with the fan/blower cable back along the ducting through the attic floor to the controller position making holes as required. The fan/blower motor cable should be rated for at least 2 amps.

8.   If you wish to hide controller system cables in walls make channels for them.

9.   The solar heat harvester room temperature sensor should be located in the same area as the return air hole and approximately 1m from the floor, you may have to make small holes in walls etc to run the cable. If there is no return air hole to the conservatory run this sensor cable to a cooler area of your home where the heated air can flow through. Run the room temperature sensor cable from the sensor location to the back of the controller location.

10.   Fit the gravity air vent(s) if any are used on the wall air exit sides of the air holes.

11.   We recommend that the Attic Heat Harvester power be fed via a separate fused (2 or 3 amp) isolating switch which is generally mounted beneath the controller.

12.   Carefully remove the front of the Attic Heat Harvester controller by loosening the four black corner screws.

13.   Disconnect the 4 way connector to the front panel mounted keypad , and put the front panel aside.

14.   The Attic Heat Harvester Controller user connections are on the right hand side inside the enclosure – see the picture above.

15.   Mark and make mounting holes in the walls for raw plugs to mount the controller, and the fused power switch.

16.   Fit the controller and fused power switch to the wall.

17.   Connect the controller cables as shown in the wiring diagram above.

18.   Carefully check all system connections to ensure they comply with the wiring diagram.

If you will use the system in a two or more floor home and need the heat in a lower floor, including a basement, you will need to pass the ducting through the upper floor(s). The system will be much more efficient if the duct run is straight or nearly straight as the air flow will be greater.

You will have to locate somewhere to pass the insulated duct, this can often be through a closet or cupboard. Make holes between the floor joists in the floors to pass the ducting through and install the system as detailed in 'Installation in a one floor home' above.

System commissioning

1   Initial commissioning can be done without the front panel keyboard being fitted.

2   Temporarily disconnect the 6 way controller connector J8 for the initial tests. Only the attic temperature sensor J5, room temperature sensor J6, and main power connector J9, should be connected.

3   Turn on the power to the Attic Heat Harvester controller.

4   If the controller is connected correctly the green Power On LED should turn on, the display back light will turn on for 1 minute and the yellow LED (top left) should blink every second. The LCD display will sequentially display a 'Sign On' message, and the 'firmware version number'. The controller then performs a self-test displaying any problems seen.

5   If problems are detected with the 230vac supply voltage or with the temperature sensors they will be displayed and you should consult the Attic Heat Harvester Controller Manual 'section 4 Systems Tests’ at for help. To select the controller 'built in test features' the front panel keypad will need to be connected. Problems need to be rectified before you can proceed to the next step.

6   If there are no problems the Current Time will be displayed as 0:00 and give you the option of setting the time using the + and – keys. This process can be aborted by pressing the front panel Mode key, then the attic and room temperatures will be displayed.:.

7   Turn OFF power to the system.

8   Connect the 6 way connector J8 that supplies power to the air valve and to the Attic Fan/Blower.

9   Turn ON power to the system

10   When room and conservatory temperatures permit the air valve will be opened. After a 30 second delay that permits the air valve to fully open the attic fan/blower will turn on.

The Attic Heat harvester Controller has many user set parameters that enable you to configure the system to suit your installation and your needs. See section 3 Parameter setting mode at

The Attic Heat harvester Controller continually monitors your systems performance, see section 2 System Performance Display mode at

Enjoy your Solar Heat Harvesting System and the heating cost savings you will have.

Thank you for helping future generations of mankind by reducing your carbon foot print.

To get the best from you system we suggest you read and become familiar with the Attic Heat Harvester Controller Manual at