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Retrofitting--home run vs 2 pipe

dave123 Member Posts: 67
Still planning to retrofit hot water rads into my current house. Seems like everyone here favors doing home runs whenever possible, seemingly for the improved flow control it gives, but I'm trying to understand when and where the advantage of home run over a 2 pipe system just isn't practical. In my situation, my 1800 SF house would need 15 rads on the main floor, and I was considering 3 low temp baseboard units for the 1100 SF walk out basement. That's 36 runs of 1/2 inch pex run along the ceiling of the basement and the ceiling of the garage, since about 800 SF of the first floor are above an unheated garage.

Five of the rads would be above the garage, so to run pex to those, big patches of the garage ceiling would need to be removed, and then replaced after the pex was run. The joist bays above the garage are packed with fiberglass.

The areas above the basement would be easier to pipe of course, but that's still 26 separate pipes running through the basement joists. And a lot of drilling.

It seems to me though that a 2 pipe system, direct or reverse return, would be far less work, use far less pipe, and be far less "in the way" down the road. But I'll defer to the experts. If experience says that the home run system is going to work far better, then I can do it. If the advantage is more of a theoretical one, I'd rather go 2-pipe.

All opinions welcome. Thanks.


  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    If it were mine, in your situation, I'd go with reverse return. Almost as easy to balance -- well, not quite, but with valves on each radiator pretty darn close -- and each radiator gets the same or very nearly the same temperature feed.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mattmia2
    mattmia2 Member Posts: 9,630
    You could also do a hybrid with some manifolds in a few central locations instead of running it all back to one location.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,828
    edited June 2020
    There seems to be a major engineering project going on here. How many millions of square feet are we talking here?

    IMO the lowest priced option is going to be just fine! Panel radiators with TRVs on a direct return will get you where you need to be. Any other overengineering will not amount to a hill of beans on a load calc of less than 60,000... especially with oversize rads. Two 3/4" zones or branches connected to 1" common boiler piping with one circulator will give you all the comfort you need. The pump you select for the system pump can be any ECM pump with a delta P setting that has the needed 6GPM to operate the system. The TRVs will do all the balancing you need.

    Boiler selection can also be just as easy. Simple will last longer. ModCon will cost a ton more, not last as long, and be more expensive to repair/maintain.

    The other Post by @dave123 indicates that he want to feel of the old Steam Rads from his previous dwelling from the 1990s. The reason we use 115% for Net rating, 40,000 BTU for 3/4" pipe, and other "rule-of-thumb" numbers in calculating this stuff is that IT'S NOT ROCKET SCIENCE!

    Whatever you do, follow the basic rules on residential systems, follow the manufacturers instructions, Pump away from the expansion tank when designing the near boiler piping, and keep it simple.

    This has nothing to do with heating systems

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
  • hot_rod
    hot_rod Member Posts: 22,120
    All one temperature? How many zones are you planning?
    It's possible to put multiple rads on a home run, the three in the basement, for example. A long as they are sized to the load and account for temperature drop.

    Same with panel rads, use a H valve with adjustable bypass, and balance multiple rads on one loop or run.

    Pros and cons to all methods.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • dave123
    dave123 Member Posts: 67
    My initial idea based on heating loads is at least three heating zones: one for the living ares above the garage, one for the living areas above the heated basement, and one for the basement itself. These 3 areas lose heat at noticeably different rates, and geographically in the house, make the most sense, but I suppose instead I could change it to two zones or even one, since all the rads and baseboard will have independent controls. It's all one temperature.

    When you say "multiple rads on a home run," you mean then a small series circuit, coming off the manifold?

    I might have to use a mod-con though, given where the boiler will be in the basement. Running a gravity vent to the roof would be really hard, whereas there's already a side vent port there I can use, for anything power vented.

    But it sounds like no one is pushing to home run these 18 emitters?

    Three direct return zones would be easiest to pipe.
  • mattmia2
    mattmia2 Member Posts: 9,630
    dave123 said:

    When you say "multiple rads on a home run," you mean then a small series circuit, coming off the manifold?

    There are a number of ways to do that. In series with sizing accounting for lower swt as you get to the further emitters, in series with a partial bypass valve on each radiator, they make them as part of the radiator valve for panel radiators, or in parallel with balancing valves.

  • Canucker
    Canucker Member Posts: 722
    I've got 19 rads in my own home and they're all connected home run style. I've had the basement ripped to the studs so it was easy to do. For a retrofit with limited access I would think that remote manifolds might have fewer places to have to open and repair but as always, it depends.
    You can have it good, fast or cheap. Pick two