I took it that your one pipe system already had a pump, so you will need a pump for the two pipe system. You may also need to install a flow restrictor valve in the flow pipe to the two pipe system, so that the one pipe system is not starved of flow.
The two pipe system from the extension ends up at the boiler(combi) in 15mm copper,i proposed to tee into the 22mm pipes at the boiler so it would be after the last return on the one pipe system.
I realise a lot of the time you can never tell the outcome until its actually connected to the boiler, as I think it may try to short cycle through the two pipe system and rob the one pipe system of flow.
I have fitted a few heating systems years ago before Corgi stepped in (rightly so) and make things tougher for non-competant people to mess with gas.
I guess my main question is, would you have piped the extra extension area in a one pipe system as the existing or went with the two pipe system?
I agree the 1 pipe system in my opinion will be robbed by the two pipe system (path of least resistance). Mixing the two types of system is not the best idea, but getting a hold of 1 pipe radiator valves is not easy. The best thing in an ideal world would be to scrap the one pipe system by converting it to a two pipe system. Is this possible? The cost would be offset in a few years by the reduction in your gas bill
In an ideal world renewing the one pipe system to two would be the preferred option,cost at the moment is prohibiting us.
1 pipe radiator valves? Thats new to me my friend,never came across those :-) Theres a difference?I vaugely remember micro bore and attaching a lenght of pipe to the valve which inserted into the rad (3/4 or 2/3 of the length) IIRC.
The one pipe system works quite well at the moment but piping the new system in two pipe was to future proof it, I'm guessing the way to balance the system to make both circuits operate efficiently would be to make both returns to be boiler flowing at the same temp/speed.
Do you think fitting a lockshield gate valve to the two pipe flow and return would suffice?
Yes one pipe radiator valves, these are valve which have a lower resistance through them. Check out http://danfoss-randall.co.uk/xxTypex/28 ... IT313.html to see these, Drayton also do this type of valve. These reduce the frictional loss through the radiator. So makeing the system pump work a lot less. As to putting a valve a l/s gate valve this will help, the correct valve is a flow regulating valve on the flow. Based on the radiator outputs you would work out how much water you would require to serve just these rads in litres/sec. and set your regulating valve acordingly. Gate valve is guess work and it could be trial & error for ever.
If you mean tee off the flow AND return pipes near the boiler, then that's not what I meant. That would make two heating circuits in parallel to each other, and one or the other may very likely be starved of heated water. That's why other posts mention fitting a second pump (as you would for underfloor heating).
I meant choose EITHER the flow or return (preferably the return) cut it and fit an elbow on each end and use one as a flow and the other as a return. Basically making a second circuit that is in series with the first ie, one big circuit. This would guarantee hot to all rads.
The critical point is of course to ensure a flow of water through the boiler at all times!! Hence the fitting of a bypass.
It could be difficult to balance the system as a whole, but nothing's going to be easy when there are two different circuits in use.
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