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Sussex Woodstoves
Blue Cedar Lodge
44 Pondtail Road
Horsham
West Sussex
RH12 5HR

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Sussex Woodstoves Water Heating Systems

Dunsley-Baker Neutralizers offer a neat solution to all the problems. 'Neutralizer' is intended to convey the fact that the neutralizer fixes the neutral point location within the system. The cold feed and open vent are both connected to the system at the neutralizing chamber and provided that both boilers are only connected through this point then pumped or gravity circuits connected to the chamber can have no adverse hydraulic interactions.

In this way, the pumped circuit from a gas or oil fired boiler will not induce flow through a solid fuel boiler via its gravity circuit. The solid fuel boiler will, however, feed hot water into the system, thus achieving the desired economy and flexibility objectives. Dunsley Baker Neutralizer Systems can easily to cope with more than two boilers on the one system and with a multiplicity of circuits including Solar or heat recovery systems. Full manufacturer’s details for Dunsley’s may be found at: http://www.dunsleyheat.co.uk/linkupsys.htm

Regarding location of the Neutralizer:

1. Conversion of existing systems is best done within the airing cupboard, avoiding general disruption within the premises.
   
   
2. Where the solid fuel appliances are on the same floor level as the neutralizing vessel, the neutralizer and hot water cylinder should be raised to achieve venting and gravity circulation.

Dunsley-Baker Neutralizers can be used to interconnect diverse heat sources such as Solar panels, Geo-thermal fluid systems, oil, gas and solid fuel boilers, depending on your design needs. A telephone call to Dunsley’s should clarify any unusual features of your proposed water system design, or ask your plumber to contact them.

Detailed pipe-work sizing will be needed for complex or extensive system, but generally the following considerations should be applied to Sussex Woodstoves boiler-heating systems.

1. On two-pipe boilers, the upper outlet is the flow, and the lower is cooler water returning.
   
   
2. On four-pipe systems, normally use one diagonally opposite pair connected to 22mm pumped flow/return pipe-work for central heating and the other diagonal pair for 28mm gravity flow/return to the hot water tank and any heat-leak radiator. If using common gravity and pumped circuit return to one connection on the boiler, these should be connected into a 22mm/28mm/28mm Injector tee using a 28mm boiler connection – this enables the pumped system to assist the gravity return flow to the boiler.
   
   
3. BS5449 specifies that a cold-water feed pipe (usually 15mm) should be connected to one bottom boiler connection and an open vent pipe from an upper flow connection should be fitted for all solid fuel systems. The open vent must be minimum 22mm pipe-work and must discharge into a “heat resistance” feed and expansion tank. Both the cold feed and the open vent pipe must enter the system separately and should not incorporate any valves, either manual or automatic, that may obstruct feed or vent pipes. This is to reduce the possibility of explosion.
   
   
4. Continuous combustion of solid fuel produced heat that must be dissipated from the boiler, even when running at a minimum level. Traditionally this has been achieved by supplying the domestic hot water tank via gravity systems but modern insulated tanks prevent this incidental use as a safety feature. In any event, the cylinder should meet BS1566 Part 1 grade 3 min with a minimum capacity of 117 litres.
   
   
5. Due to modern cylinder insulation and the use of control valves, often a further Heat Leak radiator is needed to dissipate excess slumbering heat when the hot water tank has achieved maximum temperature. This radiator to be the greater of 3kW or 10% of the boiler output. The radiator must be above the level of the stove or gravity circulation may not be at its most effective. Two full-way lock-shield valves must be fitted to this radiator so that it cannot be turned off and it must not be thermostatically controlled.
   
   
6. Where a heat-link radiator is installed, a high temperature limit thermostat should be fitted to the primary flow pipe and set to 800C so that it operates the pump for the central heating should the temperature in the gravity circuit become excessive due to the central heating being turned off with the boiler burning.
   
   
7. Time-programmable thermostats may be used to separately control the flow of central heating water through living and sleeping rooms. These will operate “open-on-mains-failure” valves to appropriately divert the hot water flow.
   
   
8. It is possible to control the temperature of domestic hot water using appropriate two-port motorised valves and a tank thermostat. Remember that the heat-leak must be increased in size if this system is used to restrict gravity flow to the hot water tank primary circuit.

Pipework design

There are 3 basic arrangements for the pipe-work connecting the boiler to the radiators: The methods are Single pipe loop, Twin-pipe flow and return systems and Micro-bore manifolds. All of these layouts will work with wood and coal burner systems. The most efficient method overall is the twin-pipe method.

General practice is for the pipe-work to be installed below the radiator. With suspended timber floors, this is no great problem as the pipes can be installed below the floorboards with the risers to each radiator passing through holes in the floorboards. The pipe-work is normally either run between the joists or across the joists through cut-outs cut in the top of the joists then protected with metal plates. Except for micro-bore systems, the pipe-work should be supported below the floorboards to avoid excessive weight having to be supported by the pipe-work itself. All hidden pipework is best well-insulated to avoid heat-losses.

Under-floor installation is impractical where the building uses solid floors. Such installations normally have high level feed pipes in the ceiling voids with fall pipes feeding single or adjacent radiators in the rooms beneath. Where the ceiling of the room is suspended, the pipe-work is normally installed between the ceiling joists from above.

This may not be possible where each floor is a separate dwelling. A third option is to run the feed pipes around the top of the wall just below the ceiling, disguised by boxing-in, with fall pipes to each of the radiators. It is never really desirable to run feed pipes around the building at floor level unless underground. Problems arise where the pipes have to cross doorways, although the pipes could be taken up and around the door frame or be buried under the floor, either of which layout is cumbersome and may create flow rate difficulties. Furthermore, future maintenance may prove unnecessarily intrusive.

Where pipes need to be installed in a loft, or under a floor, all the pipes must be insulated. Traditionally it was not normally considered necessary to insulate pipe-work below suspended floors, but energy conservation considerations nowadays make this a desirable option.

Where the level of the circulating pipe-work is above the radiators, the pipe-work circuit needs to incorporate high-level bleed valves to allow any air in the system to be released.

Single pipe loop

This is the ‘old fashioned’ way to design a central heating system. A single pipe runs from the boiler and returns to the boiler. Each radiator 'sits' upon the pipe with both connections made to the same pipe. As heated water is fed along the pipe, fluid convection (hot water rises) causes heated water to rise into the radiator displacing cooler water back into the pipe. For the system to work properly, water flow should always enter the bottom and exit the radiator top.

On single pipe loops the first radiator gets hotter than the second one etc. and the last radiator is considerably cooler as much of the water will have given up most of its heat to the previous radiators.

In principle the number of radiators on a single pipe loop is unlimited, but with more radiators, greater cooling occurs along the pipe run. The heat ratings of the radiators connected should not exceed the rated capacity of the boiler or radiator temperatures will remain disappointingly low and it may be advantageous to distribute to smaller radiators first on the loop. These systems are often used in industrial buildings where the loop pipe may be extremely large. The systems can still be found in older domestic premises but they are generally old installations and are not considered efficient.

Twin-pipe flow and return systems.

This system is more efficient over all radiators than the single pipe loop. The heated water from the boiler is fed to one side of every radiator (the feed pipe) while the other end of each radiator is connected to a separate common return pipe. This means that the temperature of the water entering each radiator is more or less the same so each radiator should heat the local environment by the same amount.
For oil & gas thermostatic systems using twin-pipe networks, a pressure relief valve fitted between feed and return pipes allows pumps to circulated water from the boiler if all radiators are shut off but for solid fuel it is better, and safer, to incorporate a heat-sink radiator with valves that cannot be shut off.

Because of the restriction of flow imposed by the radiators, the number of radiators is limited basically by the size of circulating pump. A standard pump for domestic use probably supplies up to 12 radiators. As with any system, the heat ratings of the radiators connected should not exceed the rated capacity of the boiler or radiator temperatures will remain disappointingly low.

Micro Bore pipework

Micro-bore systems use normal pipe-work for the feed from the boiler to manifolds and from manifolds back to the boiler on the return side. From each manifold, small pipe-work (normally 8mm) connects to radiators. Pipe-work between manifolds and radiators is normally kept below 5 metres, and special radiator fitting may be used so that both feed and return micro bore pipes connected to one end of each radiator.
For oil and gas systems, a pressure relief valve between the boiler feed and return pipes to protect the boiler should all the radiators be turned off. but for solid fuel systems a heat sink radiator is essential.

The advantage of micro-bore is that the smaller pipes contain less water so less heat is lost on each pipe run. Micro-bore can be easily bent during installation and does not require the same number of joints.

The disadvantages are than being small, pipes can become blocked with sediment and the pump needs to overcome increased resistance when circulating the water from the boiler so the pump is more prone to wear than with twin-pipe systems.
In hard water areas, lime-scale can build-up in any circulating pipe-work, this especially effects micro bore circulation systems and a suitable additive or water softening device is essential.

Sealed Systems

This type of system is appropriate for many gas and oil boilers but NOT for solid fuel systems in the UK. If combining heat sources using Dunsley-Baker units then the other boilers should also be open vented. A sealed system normally operates at a pressure of about 1 Bar above atmospheric pressure, i.e. about twice the pressure of an open vented system, around 30 lbs per square inch. This high pressure is achieved by a filling loop connected from the mains water supply to the system. A stop-cock in the link allows for the system to be pressurised as required and then disconnected once the system is ready. Once pressurised, the system should retain its pressure unless the radiators are bled or a leak occurs in the system.

To avoid potential damage by excess pressure within the system (which normally will only occur if there is a fault in the system), a safety relief valve is incorporated so that any excess pressure is vented direct to atmosphere, preferably to outdoors.

Anti-corrosion additives may be injected into sealed systems using a pressurised canister of the compound, now available from plumbers’ merchants. In hard water areas various devices may be fitted in the feed to the filling loop to soften the water as it is added to the pressurised circuit. Such a softening device should reduce lime scale build-up in the system. However, with a little ingenuity, conventional corrosion inhibitor products may be added either through an upstairs radiator or through a specially designed input mechanism incorporating manual stop-valves.

A lot of other-than-solid-fuel boilers are designed specifically for sealed systems and incorporate the boiler, controls, expansion vessel, pressure gauge & relief valve all within one casing. However all the various parts are available separately and it may be necessary to use separate components for large volume systems where the size of the expansion vessel needs to be relatively large.

Note that not all boilers are suitable for sealed systems – in particular do not use this method for solid fuel stoves. The manufacturers technical details must always be consulted before using a boiler in a sealed system.

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