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Rookie Mistakes - Hydronic Heating with PEX and trunk and branch?

NolanNolan Member Posts: 6
Hi all,

A first timer whose spent a number of late night, and now cold nights, learning about heating systems.

42,000 BTU with a Crown Aruba Boiler, two main supply line system (1.5” galvanized), with a total of 7 cast iron radiators. House is a townhouse, two stories, 1080 sq feet. Circ pump and expansion tank both right by the boiler.

Needed headroom in the basement and was remodeling the kitchen, so I have to reroute/scrap the main supply lines to 5 of the 7 radiators (the other two have their own lines ran). 3/5 are on second floor. Supply lines are in the thicker blue/red of drawing. Two of the second floor radiators have an initial path for their piping in order to get to the basement (open kitchen, so only one small available wall section).

I understand the appeal of a home run manifold, but not sure I want to get into that/spend the money on a manifold. I also have already ordered way too many parts as I have made all of the rookie mistakes (e.g. buying crimp fittings for PAP).

-Could I run this as a trunk and branch system using 3/4” supply PEX al PEX and 1/2” to the radiators?
-Could I use a multiport for this (ensuring outlets/piping sizes match up? Am I better off using tees?
-For the two second floor radiators already outlined on the drawing, could I tee them with 1/2” (or a 3/4”? So that I have a tee in the ceiling of the first floor (and thus have less pipes running in a wall)


  • NolanNolan Member Posts: 6
    As a note, I already have about 150’ each of 3/4” PAP and 1/2” PAP
  • hot_rodhot_rod Member Posts: 14,384
    What is the heat load?
    WAG 1080 X 25 BTU/sq.ft= 27,000 btu/ hr on design? Even at a high 30 BTU/ft you are at 32,400 BTU/hr on design day.
    Yes you can carry that load with 3/4.
    Want you want to avoid is any piping that puts all 7 radiators in series, as the last radiators output will be quite a bit less.

    How many zones? A split loop or homerun helps assure the highest SWT to each emitter.

    A room by room load calc, and review of the radiators would be a good starting point.
    It could also help you determine how low of a SWT you could get by with.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • NolanNolan Member Posts: 6
    Agreed - definitely wanted to avoid series and hadn’t made plans for that.

    I’ve gone back and forth on zoned heating. Since it’s a small house, wasn’t sure it was needed. Max would be two zones (upstairs/downstairs), but since the other two radiators aren’t tied into this, it seems simpler to just go one zone.

    I did the overall house heat loss calc, but haven’t done room by room or calculated rad outputs yet. I found a few guides through this forum that seem to offer insight.
  • ZmanZman Member Posts: 6,312
    How are you planning on balancing the system? Your layout might work well with reverse-return piping.
    TRV's might be a good idea to assure even heat between the rooms.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • NolanNolan Member Posts: 6
    I thought about reverse return, but since the runs are so short (longest is 25-30’, shortest is about 8’), I didn’t think it’d be necessary (and there are only five radiators on this piece). What do you think?

    I’d like to add TRVs, but that puts another dent in my budget. This is my starter home!
  • hot_rodhot_rod Member Posts: 14,384
    Pipe it such that TRVs could be added later on. Yes, there will always be some compromises when a budget is involved. Just try not to box yourself in for future upgrades.
    At this point you need to determine how you want, or may want to zone the system.
    You can mix and match, maybe both upstairs radiators are one zone, a single stat one zone valve, series piped.
    Maybe more individual zoning in living and sleeping spaces?

    I like TRVs in bedrooms so you have quick and individual control, possibly a homerun manifold for the lower easily accessible rooms?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • NolanNolan Member Posts: 6
    Thanks. PS I was watching YouTube videos on removing a broken pipe from a radiator and guess who turned up? You’re everywhere, Hot Rod. Thanks for sharing your knowledge.
    Erin Holohan HaskellBillyO
  • NolanNolan Member Posts: 6
    Thanks all for your help. Heat is up and running!
    Solid_Fuel_ManErin Holohan Haskell

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