Central heating is produced from the following models, but in a slightly different way according to type and requiring some variations in their individual plumbing requirements.

Heatranger Solid-Fuel models 216SFW & 355SFW

Direct, Sealed or un-vented systems must not be used with these models

With these models it is normal installation practice to pump-assist the central heating circuit, whilst retaining gravity circulation for the domestic hot water pipe-work.

The heating pipe-work should be a two-pipe, small bore system with the radiators having the appropriate control valves and lock-shield valves for balancing. The control valves may be thermostatic, but it is recommended that at least one radiator should remain in operation with a manual valve, to serve as a heat-leak

An injector tee (supplied with the Rayburn) must be fitted as shown, to ensure that the gravity hot water circulation continues even when the pump is in operation. Note the correct position for this fitting. Drain-cocks should be fitted at the lowest points of the system.

The system must be fully flushed through and filled with an appropriate corrosion inhibitor

Since radiator sizes and outputs vary considerably, it is not possible to quote the actual number of radiators that can be served by each model. It is more appropriate to refer to the radiator manufacturer's rated output and to match this to the Rayburn's specification. Solid fuel appliances often have their boiler central heating rating expressed as being able to heat a specific surface area of radiator, but it must be remembered that radiators have at least 2 sides, whilst double radiators have 4. Convector radiators with fins also increase the surface area and thus the input demand. Allow 10% for pipe-work heat losses.

The available heat to radiators and pipes from these models (in addition to domestic hot water) is:-

216SFW Assuming firebricks in winter position and spinwheel set to give maximum burning rate.
When burning solid fuel (say Sunbrite)	9.3 sq metres	4.65 kW/hr
When burning wood	5 sq metres	2.5kW/hr
355SFW Assuming firebricks set in winter position and damper in heating mode, with boiler thermostat set to give maximum burning rate.
When burning solid fuel (say Sunbrite)	29.89 sq metres	16.12 kW/hr
When burning wood	18.17 sq metres	10.26 kW/hr

• These figures are average over a 2 hour period to allow for the re-fuelling and recovery cycle.
• Control over the central heating is normally achieved by switching the circulating pump, using a time-clock and/or room thermostat.
• In the case of the Rayburn 355SFW, when the pump starts on demand for heating, the water temperature in the Rayburn will fall and this will be recognized by it's own thermostat. This will react by opening the air supply to the fire and thus increasing the burning rate.
• A suggested method of wiring the pump is given below. In each case, a low temperature thermostat isolates the pump when the firebox temperature falls below 50 deg C, thereby reducing corrosion from condensation if the fire is idling.
• A pipe thermostat should also be fitted to the flow pipe adjacent to the Rayburn, which will switch the pump on to prevent boiling of the domestic hot water, if the temperature exceeds about 80 deg C.

To prevent the possibility of the radiators becoming warm from gravity circulation when the pump is off, it is good practice to fit a check valve or motorised zone valve as shown in the diagram. In the latter case this should be wired in parallel to the pump.

The system must be installed in accordance with local water bylaws, Building Regulations and standards and we strongly encourage that the plumbing be carried out by a competent person.