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Oversizing hot water baseboard for efficiency?

Would it be wise to oversize a baseboard system in regards to total feet of baseboard (not input btu of boiler) in order to run at a lower water temp?


  • Zman
    Zman Member Posts: 7,446

    What you are suggesting is true and a good idea. Keep in mind that to maximize the efficiency, you really need a condensing boiler. Running a conventional boiler at low temps will not increase efficiency much and will shorten it's life.

    Be sure to do a heatloss calc and design each room for your target water temp. Piping base board in series, as is often done, will reduce the output of the downstream radiators. This should be factored into the sizing.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • icesailor
    icesailor Member Posts: 7,265
    Mor/Less baseboard:

    Its a really good idea. But you don't have to go all that nuts with under sizing it. Because the needed output of any heat emitter changes with the outside temperature. For example, if your design target is Zero  degrees OAT and 70* inside, and you need 10' of baseboard to keep the room at 70*, and the OAT rises to 35*, you only need 5' of baseboard. If you chose water at 180*f, to make the room 70 degrees when it is zero outside, you might only need 140 degree water when the temperature rises to 35* outside. I'm not looking up the exact number.

    You can do what you want with beer cooler wall hung condensing boilers, They will change the temperature automatically. You can also use "standard" types of boilers that need to be protected from condensation. You can use 4-way mixers that will keep the boiler above condensation but allow the system to be running below the condensation level. What is more important than anything else (IMO) is that the heat loss be calculated for balance and equal. That EVERY room and space in the building be as close to equal to each other as you can get it. That said, it is often very hard to get equal and balanced heat emitters like baseboard to balance. You may find that the room that you can get the least available wall space determines what all the other rooms will need to be in balance.
  • SWEI
    SWEI Member Posts: 7,356
    Balance matters

    I can't re-emphasize enough what was just posted above.  When we get it right, we can tune the ODR curve to the point where there is almost no need for an indoor thermostat.  Relatively common in Europe, but nobody here believes it it possible.  Proving them wrong has to be one of the better moments in this business.
  • icesailor
    icesailor Member Posts: 7,265
    More advanced than you think:


    I can tell you from experience that we, to the West of the 65th Latitude, were at one time, far more advanced that most ever knew. In 1963/64, I spent a year of my life as a Union Carpenter/apprentice on a big municipal building for the town I lived in. I learned more in that one year about basics that I have learned since. Some things I learned, I didn't know I was learning it until later. Like almost 40 years later. The building ended up on a slab for reasons. It was a two story building with a huge attic with trusses. Dropped ceilings on a wood frame, brick veneered building. Everything on the first floor was down-fed from the piping between the first and second floor ceiling. I didn't know how the heating system worked but I installed an outside sensing bulb on the North side of the building. It controlled the water temperature through an Allen-Bradley controller. The boiler was replaced in 1991. I replaced it in 2001. Nothing worked. Others had FU'ed the whole system. No one knew about the North side bulb for the Allen Bradley controller and was disconnected. It was a ODR run boiler. But there were Zone Valves and thermostats in some rooms. No one knew why. Well, the rooms with thermostats were in all East and South facing rooms that had solar gain on sunny days. With the constant circulation of the ODR, you could set the North side of the building and the zone valves took care of the overheating on the South side. The whole building was heated with 9" Cast Iron Baseboard. IBR taught anyone and everyone that wanted to learn how to do it. The land of the cheap pushed it out the door and over the cliff.

    So, you DO need those thermostats. Just for other reasons than the reasons usually given. A thermostat in every room is a waste of time, money and cost of operation. Zoning areas with thermostats is the way to go.
  • Gordy
    Gordy Member Posts: 9,537
    Thermostat for other reasons

    In Ice's example would be a thermostat serving as a High limit control.
  • SWEI
    SWEI Member Posts: 7,356
    Which we still do today

    mostly to handle solar gains, woodstoves, and crowds of people.  Worst case, someone opens a window.  Things still work, nobody's cold.
  • System piping

    Thanks for the feedback, much appreciated. I am in the process of converting my steam system to hot water baseboard. I will be using a mod-con (likely the Navien NCB). What are your thoughts on system piping? FYI my home is approximately 1500 sqft colonial. I plan on creating atleast 3 zones and was wondering if its best to do individual loops or a mono-flow setup. Ive heard the mono setup reduces stanby loss, but is that really a concern on such a low water volume system?