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Thread: Confusing Situation

  1. #1

    Default Confusing Situation

    This is long but please bear with me.

    My son spent his first winter last winter in a house he bought and found inconsistent heat on the first floor. He battled to make sense of how the thermostat worked because sometimes there was too much heat but most of the time not enough.

    So -

    I'm replacing my sons oil fired hot water boiler and I'm confused by what I see. There are 3 zones, basement, 1st and second floor of a small cape.

    The basement and second floor have baseboard in a series loop and those pose no problem.

    It's the first floor that has me scratching my head. This is a neighborhood of 65 year old homes and USUALLY they were built with a monoflow system on the first floor that also heated the second floor with one thermostat.

    What I found is all copper coming to the boiler from the middle of the house. The basement is finished so I cannot see where these pipes run.

    The strange thing is the first floor zone has a 1" copper feed and 3/4" copper return. The difference in sizes has me confused, if it's a monoflow system, it doesn't SEEM to run around the outside edge of the basement as the black pipe monoflow system does in my house.

    And to make this worse, the two bedrooms on the first floor were connected to that zone in parallel right above the boiler, so at least I can see them. They were just T'd off of that zone with standard T's, not monoflow T's. That's something I don't understand at all, I don't see how those 2 rooms got enough hot water to heat them.

    I've only done hydronics in my house where I pretty much changed everything from how it was when I bought this house but I have not seen what's out there in other peoples basements.

    So what do you guys think? Is that a monoflow system on the first floor? Should I join the 2 bedrooms into it with monoflow T's because it is or do I need to rip open the basement ceiling and see what's going on?


  2. #2
    DIY Hillbilly Southern Man's Avatar
    Join Date
    Jun 2008
    North Carolina


    Not too long but yes confusing. Since you have the boiler out and all the piping to/ from it exposed why not test which ones connect to where using compressed air? Maybe you can gather more evidence to make a diagram that will ultimately make sense to you. Also a good way to test for leaks while you are working on vintage pipes and joints.

  3. #3


    Thank you for the quick reply.

    I just got home from doping things out and what I found is a disaster. The bathroom in the basement is fed by one of the 1st floor pipes and returns to the pipe that's supposed to be the basement zone all with normal T's.

    I'm thinking the previous owner had a monoflow system that leaked and all he noticed is that things were connected with T's BC he re-connected everything the way you would domestic hot an cold water. That's what I'm seeing as I poke around. I don't think this guy understood the difference between a normal T and a monoflow T. Or that he knew what a monoflow T was.

    My work is cut out for me but now I know what I have to do. The rest of this is just doing it.


  4. #4
    Master Plumber nhmaster's Avatar
    Join Date
    Jul 2008
    S. Maine


    Most likely it's a split return system. 1" feeder branched to a couple 3/4 loops. Very common saved money.

  5. #5


    A split return system is something I've never heard of, but then again I don't know too much about hydronics.

    A couple of questions though.

    The system I cut out had 3 zone valves and a thermostat on each of 2 floors and one in the basement. It sure looked like 3 separate zones at the boiler. Would a split return system be connected that way? Does it share a return from 2 series loops? That's the rub, I'm not seeing a series loop anywhere in the basement.

    What I am seeing is how the 2 bedrooms on the first floor is connected. They each were joined into the system off of standard T's. Like this - 3/4" copper on both "runs" and the "bull" was 1/2" copper going to a convector with the other end of the convector joining back to the system the same way. Could that allow water to flow through the 1/2" "bull" with a normal T when that zone called for heat?

    Any help here is appreciated.

    EDIT: here's what I have at the boiler. Two 3/4" lines to the second floor. One 1' line and three 3/4" lines. so that's 6 lines, 2 each for 3 zones. AND the four 1/2" lines, 2 each to both radiators to the first floor bedrooms. Sure don't seem like a shared return system, there's one too many lines for that. I don't know why a 1" line was used, it doesn't feed a monoflow system and maybe this isn't a split return system either. Maybe the guy who did this was confused too, as I am by what he did.

    Last edited by sibi1972; 10-08-2008 at 09:07 PM.

  6. #6
    Computer Programmer Bill Arden's Avatar
    Join Date
    Sep 2006
    MN, USA


    You can make a mono flow system without using monoflow T's, but it won't be as good.

    It's a matter of making sure you have enough restrictions between the two T's to get the desired flow ratios.

    It sounds like the system is very complicated without enough control points.

    As I see it, you have two options
    1. Diagram it out and decide what areas need more flow and what ones need less. Then add valves where you need to reduce the flow rate.

    2. Add more zone valves and possibly even a "Normally open" zone valve to direct the flow where you want it.
    Important note Ė I donít know man made laws, just laws of physics
    Disclaimer: I'm a big fan of Darwin awards.

  7. #7



    Thanks for the advise but I think I'm going to open the basement ceiling where I need to and find the connection points to the basement and 1st floor and just make 2 series loops. I know that's not elegant or the most efficient but with as small as these zones are, I'm thinking I'll get away with it.

    Whatever system is in place now resulted in the basement being 85 degrees all last winter and almost no heat to the 1st floor and the old boiler ran through way too much oil.



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