Monoflow loop - moving a convector - couple of q's

Discussion in 'HVAC Heating & Cooling' started by scott_r, Jul 31, 2009.

  1. scott_r

    scott_r Cursed Dilletente

    Dec 17, 2007
    Heya gang - it has been a while since I've posted.

    I'm in the middle of a project to replace my boiler (a 1942 National Radiator Co., Johnstown, PA lump) with a nice new Munchkin modulating/condensing boiler. I'm paying professionals do to the boiler install which involves new: boiler, circulators (going from a B&G??? to dual Grundfos variable speed) , expansion tank, spirovent (yay!), and a DWH storage unit run off the Munchkin. I'm excited to really drop my heating bill!

    One of the problems with the old system was that there was too much radiation in the old living room - the central large room in the house - for two reasons: first, a back outdoor porch was closed in, so one one of the radiators (convectors, really) which had previously been under an exterior window, was now on an interior wall; second, the house has been considerably insulated since the original system was put in (storm windows & doors, attic and some in-wall isulation). The old system was constantly short-cycling - only ever got up to 140F at best - and the enclosed back porch was generally always cold - only one tiny convector was relocated to that room.

    So, I'm moving the 5' living room convector out to this florida/family room. It's almost a straight shot extending the supply lines off the loop. I went with the convector as it appears that it puts out a heck of a lot more BTUs/ft. than something like a finned tube baseboard product, and I already have it. It also looks like the flow resistance of the convector will be a lot lower - and this brings me to my question(s).

    The original supply lines for that convector - a National Radiator Co., 5', 3-tubes + fins - are 1" steel. I'll be extending one straight run of those lines, w/o adding any extra els, a total of 30' (15' for supply, 15' for return) to the new location.

    1) I'd prefer to change to copper from steel (easier for me to cut and sweat).

    2) I'd like to switch to 3/4" pipe

    3) I'd like to avoid removing the single regular T for the existing supply (there is a B&G monoflow T on the return).

    I'm fearful that I'm adding so much "head" with the extra length that adding even more by stepping down in pipe size will really hurt me. I'm not sure if the static friction of copper is lower or higher than steel. I'm sure the difference in head is greater but it might be too small to be significant in this case...I'm curious what thoughts you guys have.

    My installer said there would be no problem extending the 1" with either copper or steel (and he's using copper for all the sections he's replacing), so I guess the real question is about the 1" vs .75" - oddly, the smaller convectors all have .75" supplies, but given how incredibly oversized the original system was, I'm kind of doubtful that much attention was paid to this level of detail anyway.


  2. scott_r

    scott_r Cursed Dilletente

    Dec 17, 2007
    Following up my own message...

    Well, I guess nobody wanted to take a guess or I violated the posting policy (my apologies for that if I did). I decided to take the least risk possible and went ahead and used 1" copper (sched. L), though this was a tighter fit. I will post the results when we pressurize and fire up the system.
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