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Have just bought a house in which we've inherited a hydronic system - so just beginning diagnosis and diagramming, etc.

It seems that radiators use only one line for both supply and return; presumably valves in each radiator regulate flow to that radiator? Apart for a need for balancing the whole system - some rooms are too hot, others cold - it basically works.

Longer-term vision for system is to break it up into 'n' zones; individual valves, and I imagine, dedicated return line. At this point, house has only two zones, so much work to be done in warm weather!

Does this sound like a crazy setup? An ad-hoc kind of installation?

DrLou
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  • It sounds odd, since most water type systems need two lines to make a loop, or one line in a loop(radiator to radiator then back). Having two lines in one pipe seems inefficient since the cooler return will cool the supply. Can you provide pictures. – crip659 Mar 28 '23 at 20:21
  • A single line doesn't make any sense. How could you possibly replace the cool water in the radiator with warm water through a single line? – brhans Mar 28 '23 at 20:25
  • That doesn't work and makes no sense, because the hard part is finding the route/pathway for the pipes - once you have that, 2 pipes is no harder than 1. The only way 1 pipe can work is if the radiator has huge volume (large enough to absorb the cool water in the supply pipe and still receive enough hot water to usefully heat), and then the furnace pushes this slug of water back and forth. – Harper - Reinstate Monica Mar 28 '23 at 20:36
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    Another possibility (apart from the monoflow system Ruskes mentions) is that the system is steam, not hydronic, where a more literal "one- pipe" (not even a loop) is quite common - steam rises to the radiators, condensate flows back from them. Look Ma, no pumps! But steam systems are becoming rarer with time for logical reasons.... – Ecnerwal Mar 29 '23 at 03:05

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You have a One Pipe System and it looks and works like this

one pipe heating

one pipe

Suggest to Read the article, it nicely explains the details.

The main drawback is there is a temperature drop at each radiator feeding back in the single line thus reducing overall heat supply. Thankfully each radiator has a thermostatic valve for individual control.

asinine
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    Usually called Monoflow and it's important to know the tees are not just tees, they are special and the flow and return ones are installed differently. There's nothing wrong with this system but it's not easily cut up into zones. – jay613 Mar 28 '23 at 21:20
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    It does have "per radiator" zoning ability with the thermostatic control valves, though. Won't suit people who buy into "$mart thermo$tat$," works fine if you like your thermostats dumb and the valves are in good repair. – Ecnerwal Mar 29 '23 at 15:19
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    Thanks so much for all responses - you guys are great! Yes, indeed - that 'one pipe' diagram above is schematically what we have... $Ruskes comment I think summarizes my findings; that heating is wildly different at different points in the circuit. $Ecnerval - Yes, a sophisticated 'n' zone system, under IoT control, is precisely the goal of this exercise - though not this week! I'm thinking - eventually - individually-controlled pumps(?)/valves(?), perhaps even on a per-room basis. I think a lot of efficiency could be achieved in this house... – DrLou Mar 29 '23 at 21:15
  • That's a really good article thanks. – jay613 Mar 30 '23 at 01:24
  • @DrLou Use the `@` to ping someone, no need to ping the answer author - they're automatically notified. Also, be sure to say "thanks" properly but up voting answers, and giving a check mark to the one that helps the most (you may want to wait 24 to 48 hours to see if additional answers show up). – FreeMan Mar 30 '23 at 14:29
  • One thing worth noting - I have also seen one pipe systems with no monoflow tees or anything like that, so the radiators are just daisy chained one after the other. It is definitely worth checking to see if your system is using monoflow tees, because if it isn't it is pretty hard to balance the system, because restricting the flow at one radiator restricts the flow for all of the radiators. – zelinka Jun 16 '23 at 18:49
  • @zelinka That's **not** Monoflow - that's a baseboard loop, and the balancing is done by adjusting the airflaps on the baseboard over the finned pipe. Vaguely similar looking but entirely different to operate. – Ecnerwal Jun 16 '23 at 18:52
  • Yes that is what I was saying - you need to be able to differentiate between if the system has monoflow tees, in which case you can adjust the flow to an individual radiator, or if it lacks monoflow tees, in which case the flow rate throughout the entire system is uniform. It is worth nothing that I have also seen systems that are basically baseboard loops with cast iron radiators, which don't have fins or anything else to adjust their heat output. – zelinka Jun 20 '23 at 17:03