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Question about Laars IO Manual piping concept w/Indirect

Boon
Boon Member Posts: 247
Hey all, A previous post I saw talked about piping a Laars FT, I had some questions about it so I took to the IO Manual, which didn't help:

The piping diagram on a single boiler install (pg 43 & 45) with an indirect shows the indirect's return getting piped to the boiler output (attached diagram, left side). I would expect the indirect's return to be piped to the boiler return. I thought the piping concept in the manual might be for hydraulic separation. But when I looked at the cascade piping diagram (pg 46, attached diagram, right side), it shows the DHW return being piped into the leader boiler's return; if hydraulic separation was important for a single install, why wouldn't it be important on a cascade install? and/or why is the single boiler shown piped this way?

Can someone explain what/why there is a difference? Thanks

DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.

Comments

  • Ironman
    Ironman Member Posts: 6,323
    edited April 2020
    W/M shows a setup like the one on the left as an option. I really don't see the benefit unless the indirect tank and its circulator are too small/large to move the necessary gpm through the boiler by themselves.
    Notice that both the primary and indirect circs have to run simultaneously during indirect tank charging.
    I don't think hydraulic separation is an issue either way.
    Most indirects call for the supply (hotter) water to go in the top to heat the hotter tank water. I don't think it's essential since I have TT Smart tank drawings that show it both ways depending upon the piping arrangement.


    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    Boon
  • hot_rod
    hot_rod Member Posts: 14,552
    I prefer direct Parallel pipe like the second drawing

    In the first drawing I suppose the heat and indirect could run concurrently, The other negative would be the indirect is seeing a blended temperature. Two circulator need to run also.

    Piped parallel it gets full boiler output, temperature and flow , quickest recovery
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    Boonfenkel
  • Ironman
    Ironman Member Posts: 6,323
    The W/M Ultra has a head HX and REQUIRES p/s piping, the Laars Fire tube is basically the same boiler as the UFT and does not have a high head HX. IDK why the drawing in the Laars manual is showing p/s to the indirect. Maybe an error?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Boon
    Boon Member Posts: 247
    Thanks gents,
    Ironman said:

    Maybe an error?

    I thought it was curious, too, that they reversed the top/bottom/ins/outs on the indirects in each diagram.
    DIY'er ... ripped out a perfectly good forced-air furnace and replaced it with hot water & radiators.
  • GroundUp
    GroundUp Member Posts: 1,132
    Ironman said:

    The W/M Ultra has a head HX and REQUIRES p/s piping, the Laars Fire tube is basically the same boiler as the UFT and does not have a high head HX. IDK why the drawing in the Laars manual is showing p/s to the indirect. Maybe an error?

    Because the Laars FT comes with an internal primary circ, unlike the UFT. They will allow direct piping if the minimum flow rate is met, but they still come with a factory installed 15-58
    Ironmanfenkel
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