Designing open vented system

[pas le plumbier]

Hello to all. Notwithstanding some people’s views on open vented gravity centralheating systems I am in the process of designing such a system to run of mywoodturning Rayburn. I have spent sometime considering the options and various safety aspects of such a system butwould appreciate a little clarification on some finer points of detail.
First point, I amaware that on the gravity section of the system the flow pipes should risecontinuously but I also note that in order to eliminate air being trapped inthe system the pipe ‘t’ing off to the heat sink should fall slightly, acontradiction in my view. Do I assumethat if there is sufficient rise first and the slope is minimal this will notaffect the thermsyphon? Iam planning on installing an air separator so would this negate the need toslope the pipes anyway? Would there beany significant affect in ‘t’ing off the heat sink before or after the DHWcoil?
Second point, Is thepositioning of the injector tee critical, (in relation to the stove) if so whatdegree of leeway is there? The Rayburn will be on the ground floor but thecentral heating flow and return will branch off on the 1[SUP]st[/SUP] floor, itis a two tapping boiler.
Finally, for now! Ihave seen a number of different layouts where the central heating pump is positionedeither on the flow or return, which would be the most advantageous? This also applies to the low limitthermostat, again which would be best? Rayburn show this on the flow but other informed sources state return,personally I would have thought the return would be best as it indicates thewhole body of water is to the required temperature but I would appreciateclarification.
I hope this is not toomuch of ask for my first post and if the questions appear a little naive I do apologise.

 

[joni os]

On gravity side of system, flow and return needs to be vertical," rise continuously" will not do if it implies horizontal displacement exceeding 1 metre. Ensure your DHW cylinder is this close to being vertically above boiler. Pipes should be 28mm or larger and flow goes to top of coil and radiator, heat sink, and exits from bottom tapping. Vent should be vertical continuation of flow pipe from boiler until it bends over above F & E tank . F & E tank needs to be metal or otherwise not liable to deform due to hot water. Any fall to heat sink needs to ensure air can escape direct to vent.

 

[Best]

It is not a job for DIY - really need it installed very professionally with someone that understands how to do pipework and gravity solid fuel circuits.
The tee off should be falling, and it sometimes can actually be beneficial to have the tee off higher than the coil (even when not essential) both to aid easier install and actual gravity circuit circulation.
The injector tee is usually best immediately at heat source if a 4 pipe arrangement is to be connected to 2 pipe boiler. The thermostat to work pump is normally required on return where it leaves cylinder.
The pump can be installed on either flow or return, but less heat is better for pumps, so return is IMO preferable.

 

[pas le plumbier]

On gravity side of system, flow and return needs to be vertical," rise continuously" will not do if it implies horizontal displacement exceeding 1 metre. Ensure your DHW cylinder is this close to being vertically above boiler. Pipes should be 28mm or larger and flow goes to top of coil and radiator, heat sink, and exits from bottom tapping. Vent should be vertical continuation of flow pipe from boiler until it bends over above F & E tank . F & E tank needs to be metal or otherwise not liable to deform due to hot water. Any fall to heat sink needs to ensure air can escape direct to vent.

Thanks for the reply, got the 28mm pipe covered and metalF&E with copper float ball. Ho****er cylinder will be more or less above the boiler and it is my intention toplace flow and return on heat sink top-bottom, left-right. Thank you for the clarification on thecontinuous rise, I was just confused (although I understand the logic) why someschematics advocate a slight fall from flow/vent to heatsink if this is not desirable. Any expansion on my other points wouldbe gratefully received.

 

[pas le plumbier]

It is not a job for DIY - really need it installed very professionally with someone that understands how to do pipework and gravity solid fuel circuits.
The tee off should be falling, and it sometimes can actually be beneficial to have the tee off higher than the coil (even when not essential) both to aid easier install and actual gravity circuit circulation.
The injector tee is usually best immediately at heat source if a 4 pipe arrangement is to be connected to 2 pipe boiler. The thermostat to work pump is normally required on return where it leaves cylinder.
The pump can be installed on either flow or return, but less heat is better for pumps, so return is IMO preferable.

Sorry I had not seen your post before my last reply. Thank you I have noted your words of caution re: using a pro. and to some extent I agree but the reality is I will be doing this myself and wish to do the best job I can, hence the desire to obtain has much information as possible. I acknowledge that I am not a plumber and I am not conceited enough to imagine I know everything but without boring you with my life experiences I have some experience with plumbing etc. In a previous life I used to manufacture copper cylinders for example. Thank you for some useful points I will take them on board, much appreciated.

 

[joni os]

If air gets into heat sink, circulation could be cut off, hence fall required from vent. Pipework requires continuous fall so as not to create airlock between heat sink and vent. Fixing, left/right, corner to corner, is a matter of some debate. I've known radiator 1.800 metres long, fixed top and bottom, same side, work correctly for so long it was a 6' foot radiator when first installed.