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Series Loop vs 2 Pipe Direct System

Hello to all, Im Gary from Chicago, just looking for some help with my radiator issue. I have a hot water boiler with 3 zones and a pump for each zone and a Taco switching relay. 1 zone goes to my 1 story addition on the back of the house with a crawl space underneath.

To make a long story short, I replaced the cast iron baseboard radiators that were in that room and added 2 walls of slant fin copper radiators (approximately 20' total). The problem is when the temp drops below 25f outside, the thermostat in this backroom won't go above 65f. We do have a little electric oil radiator that we plug in and that gives off enough added btus to allow the thermostat to reach whatever desired temp.

I have 10' of extra radiators I am getting ready to install in that room on another wall. My main question is how would you guys run the piping. Currently I have it in what I understand is a 2 pipe direct system. I eliminated all the old galvanized piping that was in the crawlspace and changed it to 3/4" copper.

I am wondering if I should keep the piping the same way when I add this extra 10' or run it in a series loop. The extra 10' of radiator will bring me to about 30' total. The crawlspace is not below grade and is only insulated with very thin fiberglass insulation between the floor joists. I did insulate all the copper with 1" fiberglass( 1" or 1/2", cant remember).

Here is a diagram of the piping that I currently have.

Comments

  • hot_rod
    hot_rod Member Posts: 17,510
    You could put those 3 in series, feed one to the next to the next

    with your proposed piping you may need to add balance valves to get adequate flow to each of the 3
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,637
    Agree with @hot_rod . You only need a total flow of about 1.7 gallons which 3/4 will easily do. So you can put them in series or pipe them as shown and install two balance valves. 3/4 copper will support about 70' of baseboard so your well within that.

    I would suggest adding insulation between the floor joists will be a big help
  • stupidhomeowner
    stupidhomeowner Member Posts: 15
    Thanks for the replies gents, I am not educated on balancing valves at all, where would I install those?  Can those be in the crawlspace or do they have to be up by the radiators?  Do you guys think it’s necessary?
  • mattmia2
    mattmia2 Member Posts: 6,637
    Maybe you should start with a heat loss calculation to see how much baseboard you need to cover the heat loss.
  • stupidhomeowner
    stupidhomeowner Member Posts: 15
    mattmia2 said:
    Maybe you should start with a heat loss calculation to see how much baseboard you need to cover the heat loss.
    Any good tips on calculating heat loss?  It’s a 22x14 brick extension with a crawlspace that’s above grade.  Closed cell spray foam insulation in the roof rafters, fiberglass bats in the walls and floor joists.  Bay window and 2 normal sized windows.  I think the btus I currently have are somewhere around 13k.  I’ll have to double check.  If I add the extra 10’ it will put me at an additional 5k btus.   
  • mattmia2
    mattmia2 Member Posts: 6,637
    Slant Fin has a calculator. There are others too. Is this fin tube on its own zone? Fin tube heats very differently than standing cast iron radiators and if the 2 are on the same thermostat it will be very difficult to balance the 2.
  • stupidhomeowner
    stupidhomeowner Member Posts: 15
    mattmia2 said:
    Slant Fin has a calculator. There are others too. Is this fin tube on its own zone? Fin tube heats very differently than standing cast iron radiators and if the 2 are on the same thermostat it will be very difficult to balance the 2.
    Yes it’s on its own zone which has its own pump also
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 4,237
    This is the piping design I would use for your situation. All 3/4" until it gets to "shared piping" back to the boiler room. Shared piping or manifold may need to be larger based on required gallon per minute (GPM) requirements.
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org

  • hot_rod
    hot_rod Member Posts: 17,510
    How many feet of cast baseboard did you remove from the room? The copper fin tube of the same length should do the job.

    30' of BB should get you around 15,000 btu/ hr, @500 or so btu/ ft.

    The room is around 308 sq ft? Seems like a very high load in the room, 50 btu/ sq. ft?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • stupidhomeowner
    stupidhomeowner Member Posts: 15
    This is the piping design I would use for your situation. All 3/4" until it gets to "shared piping" back to the boiler room. Shared piping or manifold may need to be larger based on required gallon per minute (GPM) requirements.
    So this would be series loop as I understand it.  Being that I would have only 30’ of radiators, is there any need for bypass valves or a trv?  I wouldn’t be able to fit those in the end caps I have anyways but I’m not sure if they would even be necessary with only 30’ of radiators.  A couple guys on another forum recommended it.  

    So the 3/4” copper supply and return change to 1” galvanized once it leaves the crawl and heads back to the boiler.  

    I like this option of piping but I’m just worried that the last radiator in the chain would be running colder water than the first.
  • Jamie Hall
    Jamie Hall Member Posts: 19,935
    The last radiator in the series will run on cooler water, but if theyare all in the same space it doesn't really matter.. Do, however, try to adjust the flow rate so that you get the desired delta T from the loop.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • stupidhomeowner
    stupidhomeowner Member Posts: 15
    The last radiator in the series will run on cooler water, but if theyare all in the same space it doesn't really matter.. Do, however, try to adjust the flow rate so that you get the desired delta T from the loop.
    Would you mind elaborating on how to adjust the flow rate and what is a delta T?  I’ll do some googling myself in the meantime.  Thank you 
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,637
    @stupidhomeowner

    baseboard will produce around 550 btus/foot of finned length. get the total btu by adding up the installed baseboard footage x 550 and divide the total btus by 10000 to get the gpm of water flow you need.

    so for 30' it would be (30 x 550) divided by 10000=1.65gpm. Not super critical in you application. You just don't want to over pump excessively.
    stupidhomeowner
  • Jamie Hall
    Jamie Hall Member Posts: 19,935
    There should be somewhere--probably down near the boiler-- valves which can be adjusted to change the flow. As @EBEBRATT-Ed said, you want around 1.6 gpm. But ut us just as satisfactory to measure the temperature difference of the pipes between the beginning of the loop and the end. That's delta T, and you want somewhere around 15 to 20 dgrees F
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • stupidhomeowner
    stupidhomeowner Member Posts: 15
    There should be somewhere--probably down near the boiler-- valves which can be adjusted to change the flow. As @EBEBRATT-Ed said, you want around 1.6 gpm. But ut us just as satisfactory to measure the temperature difference of the pipes between the beginning of the loop and the end. That's delta T, and you want somewhere around 15 to 20 dgrees F
    What would you recommend to test the temp difference?  A digital thermometer?