Hi All, I am so glad I found this forum whilst looking for advice on the net. I am not a plumber as such but I do know a thing or two about DIY. Our house is a 1937 built detached which had a central heating system installed in probably around the early 80's, originally oil boiler system. But now this has been converted to a newer condenser boiler, a Vaillant 938 to be precise. Our heating works very well and throws out a lot of heat, we have really old style long radiators (2.5m wide) but they do warm the house up really well. The system is on two zones, with an upstairs and downstairs circuit run off two individual Nest thermostats again work brilliant no issues at all. This weekend my DIY part of me has decided to install 2 new radiators into our second hallway and utility room. I have used the online BTU calculators and bought the following from Wickes in terms of best output and what can be fitted in the space we have: - Rad 1 - 600(H) x 800(W) Rad 2- 600(H) x 900(W) All these rads are the Type 21 slim double style ones. We have a family member work for Wickes so with a nice 20% staff discount they came out at a decent price. TRV's I already have new spares (Drayton) the fancy expensive ones, although we never control our heating with thermostats. They always run on open full, as they never have seemed to work right and now I probably know why. We have only been in the house for a year so still tinkering away with DIY projects and discovering new things - the house really is a world of wonders! Luckily we bought it off the chap who's father had the house built from scratch and he lived here with his father ever since a child and we have regular contact - so know a lot about the homes history. I am going to get a plumber in to do the job (pipework) and have already been quoted by 3 of them who all have their separate opinions with is why I am here to ask the professionals. I will be putting the rads onto the walls as I have a bit of OCD and want them to be fitted perfectly and straight. All plumbers have agreed to this and said would come and simply solder up the pipework. Before calling the plumbers in I went into our crawl-under cellar which houses all the pipework for the downstairs and I though it would be a simple matter of hooking the new rads up to the Flow and Return by tapping a 15mm into the 22mm main pipes that run right across the cellar of the house. But to my shock the house is on a one pipe system. This now explain why the hallway and kitchen radiator always take longer to heat up than the rest of the system, as they are the last on the run! Now the flow and return pipes for the main house heating system run from the garage where the boiler is and go through the utility, store room and second hallway and we would be tapping into the flow/return pipes from under the basement in order to hide the pipes as best as we can. I have attached 3 pictures, one of the system how it is currently and two further pictures of what the plumbers have proposed. But I am yet to find out which is the correct one that will work properly. We do not want to loose any heat from the house main radiators, and we just want these extra 2 rads to break the chill in the other 'outbuilding' areas . So my understanding from 'common sense' was that hooking these two new rads to the return pipe would be the best way forward as eventually they would get hot once the water has made its way around the system all hot and warm, just like the kitchen and hallway one do. But one thing I will note is that we changed the main hallway radiator for a new Type 22 radiator and although it gets very hot eventually, the bottom is always cold and I have tried everything to rectify this and only this weekend I have found out it's on the last leg of the return pipe on our one pipe system! I read somewhere that Type 21 and Type 22 are no good for one pipe systems, but not sure how true this is. The good things about the system is that if we turn off a rad at the valves it dos not **** off the system. As you will see in the pictures there is a main 22mm pipe what goes around the system and each radiator is spurred off this using a T 22x15x22 going into each radiator. So I was hoping to do the same but instead this would be on the Return flow very close to the boiler, as the return pipe and even flow pipe have about 4-5m stretch before they reach the main house circuit. However further into this I am unsure how it would affect the upstairs too as I cannot make a diagram of this as we have had new carpets down which I do not want to rip apart just yet. Another thing I would like to add is that the house has a total of 11 radiators (pretty large ones too) and out of them 11 rads, 2 down stairs ones are fitted with top entry and all the upstairs barring then towel radiator are also top entry for some strange reason. What are your thoughts on this? Oh and by the way the 3rd plumber has completely disregarded the job and said we would be better off with electric heaters which I am not going to do. Lastly changing over to a 2 pipe system is an option downstairs as it's easily doable in the basement, but not upstairs. Although I would like to keep this 1 pipe system and just add the extra rads to make life easy. Then when and if we do a big renovation we can change the whole piping system for the better one. Please also be easy on me it's only my first post! haha Thanks in advance!!!