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baseboard sizing with MOD-CON boiler

Mikejci Member Posts: 1
I m installing a new hot water baseboard system and using a gas fired 5to1 turndown mod-con boiler. I will be using the factory reset control and have sized the baseboard for 180 degree water. Is this correct? Someone suggested sizing for lower water temperature 130-150 degrees saying I will be able to take advantage of condensing boiler efficiency at those lower temperatures. I think the baseboard will be oversized when design is met( 0 degrees oa-t) and that won't be often but won't the reset control keep water temps down on less than design days? That should keep the return water temp down to condensing temps (130) Any help would be great. Thanks


  • Gordy
    Gordy Member Posts: 9,546
    If you design around 180 for the baseboard then don't expect to condense at design days or close to design temps. Yes you will pick up some efficiency when you get into condensing range sub 130 return temps and lower. By overs sizing the base board you insure that condensing return temperature point is met at colder OAT.

  • Ironman
    Ironman Member Posts: 7,379
    edited December 2014
    If you're designing with a 20* delta T (most common in the U.S.), then you want to size based upon 170* AVERAGE water temp. Using 180* is a common error that will cost you about 13% in capacity.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Paul48
    Paul48 Member Posts: 4,469
    It's equally important to size the boiler correctly. What we see a lot,is people taking their heat loss figures, then going larger still,"just to be safe". It's a 'big' mistake. There is maybe 20% fudge-factor built in to most heatloss programs, to begin with. Or, they massively oversize to satisfy an indirect for DHW. That's another big mistake, and sadly, it is usually a contractor talking someone into doing that......Don't
  • bob eck
    bob eck Member Posts: 930
    Check into copper baseboard line called Design Line Synergy A Mestek Company.
    GPM 120* 130* 140* 150*
    4 328 411 502 597 BTU FOOT
    1 312 390 477 567 BTU FOOT


    Look under Synergy

    If you use 150* 567 BTU per foot on design day you should be able to keep your boiler condensing most of the heating season.
    I would avoid very small zones.

    Has any contractors used a product called boiler buddy?

    F W Webb should be able to get your contractor this copper baseboard product.

    Stay warm.
  • ced48
    ced48 Member Posts: 469
    Heck, I'm heating with 110 degree water at temps above 30, and adding a degree from there down to design, 5 degrees, 135 degree water. I am always in a condensing mode. You do not need those high temps.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    My house has radiant slab downstairs and baseboard upstairs. It was a single zone system. It was always too cold upstairs. It has low heat loss up there, but 3 feet of baseboard in each of two rooms did not provide enough heat when provided with hot water at radiant slab temperatures.

    When I replaced my 55 year old boiler with a mod-con, I decided to split the system into two zones, and I wanted to run the system at the lowest possible temperatures I could. Hotter in the baseboard zone than in the radiant slab zone. So I put in 14 feet of Slant/Fin baseboard into each room, that permits me to run 140F supply to the baseboard when it is 0F outside. Design temperature here is 14F, and I saw it get down to 2.8F for a couple of hours last heating season. It had not gotten below 8F in the 4 years before that. On a design day, the water temperature supplied to the baseboard zone is 132F. The return temperature is less than the supply, of course.

    For my system, also with 5:1 turn-down, this is not enough turn down. Especially in the fall and late spring. But for maximum efficiency, you should run with the lowest possible temperatures consistent with getting enough heat. I am not a heating professional, but I suggest installing as much baseboard as you have room for. We do not discuss price here, but for my system, the labor cost more than the baseboard. If I had any more baseboard installed, it would have had to turn corners and the labor cost would have gone up some.

    Depending on how you balance the heat delivery to each room, you may need to make the length of the baseboard proportional to the heat loss in each room.
  • icesailor
    icesailor Member Posts: 7,265
    ced48 said:

    Heck, I'm heating with 110 degree water at temps above 30, and adding a degree from there down to design, 5 degrees, 135 degree water. I am always in a condensing mode. You do not need those high temps.

    As long as you have enough lineal baseboard, that works well.

    If you design and install for 170 degrees, and try to run it at 130, you might be needing to turn your system temperature up.

  • ced48
    ced48 Member Posts: 469
    edited December 2014
    If you go by the published Btu output of your baseboard, compared to an accurate heat loss survey, most are way to heavy, you will find you don't need that much more baseboard than most contractors have been using for much hotter water temps for years. My system uses only sixty feet of baseboard, a small house, 800 square feet, with some additional allocation for a walkout basement.
  • Rich_49
    Rich_49 Member Posts: 2,766
    Also remember that each piece of baseboard after the first recieves eveb lower temp fluid than the last so the farther you go away from the boiler the lower the temps get . Have seen many systems designed for a 20* Delta and actually achieving 40*+ Delta . rooms at the return end never satisfy because the SWT by then is too low .
    * Mod Con and baseboard , Low temp ,130* at design use a manifold so all baseboards receive same temp . feed with 1/2 pex between radiation and manifold , use Smiths heating edge baseboard and a tee at each end to feed through both tubes . 1.5 gallons per minute per baseboard and a Delta T pump . Enjoy your efficient system .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • archibald tuttle
    archibald tuttle Member Posts: 1,085
    i always thought it was a sin to pit in cover without element. if i have a room that doesn't have enough wall compared to others then i double the element rather than reduce element in the other rooms for balance. you virtually can't put too much.
    Jean-David Beyer