There is absolutely no problem running a 1 inch primary flow pipe from the stove/boiler up into the attic and running horizontally until dropping down in to the hot press area and connect to the cylinder. The 1 inch primary return can be ran under the floor and up into the hot press and connect to the cylinder. This circuit will indeed be free from any valves or pumps. This circuit will work perfectly well once the dip in the return pipe will not exceed one sixth of the circulating height between the centre of the boiler/stove and the centre of the hot water cylinder.
I disagree. What happens if there is a circulating pump failure or a power cut? The heat will rise and travel to the point where it must drop. The heat will back up within the solid fuel boiler and boil. This will cause banging and possible joint leaks. It will also cause enough expansion within the circuit to pitch from the OVSP back into the expansion tank, re-oxygenating the system, causing sludge and rust.
A well known case in the UK was where this happened, the heat melted the expansion tank, it leaked and scalded to death a sleeping baby below it.
Just because it is commonly installed does not make it right. Do you not remember all the cylinders fitted in a cupboard in the living room close to the back boiler to ensure a gravity circuit? There was never an issue as there was no circulating pump in the first instance so it had to be installed correctly.
To explain, when water is heated it becomes less dense that cooler water resulting in the heated water wanting to naturally rise. The circulation of water can be achieved by convection currents being set up within the flow and return pipework, resulting in a natural circulation. Do not get me wrong, a fully pumped system is by far more the better option and it is against Building Regulation to install a heating system unpumped. However, allowances in solid fuel systems must have the ability to disapate heat when there is a pump failure or power failure.
The pipework will have to be metallic and be installed using as many bends as possible to ensure proper circulation.
This system was used extensively because in most bungalow design the cylinder was located in the hot press area which was 6/10m down the hallway. All solid fuel boilers will boil if the circulation is not assisted with a heat leak gravity heating circuit/radiator or by using a circulator.
Bends must be kept to a minimum. The maximum pipe length permissable is 25.5ft or 7.8m between the boiler and the cylinder coil. It should also be well lagged. This is ensure the velocity of the circuit to the coil. Each 90 bend (from horizontal to vertical & from horizontal to horizontal) is equivalent to 4ft of the total allowable length of pipe run. Therefore 3 x 90 bends = 12ft, so now the total allowable length of pipework is now halved! Bends from vertical to horizontal should preferably be made with a pipe bender rather than an elbow joint to allow a sweeping bend. 90 elbows are, of course, acceptable.
I have mixed views on non-return valves. I cannot see a problem with spring type walves as they can be fitted on any plane once in the right direction. Flap type valves have a habit of passing.
I agree somewhat but only if they are located in a suitable position. Spring type should not be located on the flow pipe close to the boiler as excessive heat can melt the plastic inards of the valve. I have no problem installing them on the return pipework between the pump and the boiler where temperatures are cooler and only if of course the pump in this situation is located on the return.
Flap types should not pass if they are located on the driving side of the pump and close to same.
Down through the years I have fitted many a dual system in a bungalow and I have had no problems with restricted circulation.
The installation installed in the way you have described will of course work each and every day as long as there is a circulating pump in operation. My argument and Building Regulations willl argue what happens when there is not and who will suffer the possible consequences of it!
A little test for anybody who has this installation: Light a good fire and switch off the pump. The amount of installations that I have seen where the pump is wired through a switch and not a pipe thermostat and when I have asked the homeowner when do you switch on the pump, the reply is the pipes tell me (banging!).
I would stay away from garden hose/ pex pipes on the primary circuit.
I completely agree. They cannot take the heat and will sag and melt. Also do not use push fit connections. The plastic inards can also melt.