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Mod con return temps

Recommendations on lowering return water temp in finned baseboard sytem with mod con boiler


  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
    Lower the supply temps as much as possible, while still providing enough heat. You might have to install more baseboard... or lower your buildings heat loss
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
    sludge said:

    aquastat settings 160 low limit 180 high limit

    That's not going to work... I'm assuming he's asking in hopes of lowering his return temp down to condensing levels (~130* and lower).

    To the OP is your system setup with ODR? Need more details on setup.
  • remodel
    remodel Member Posts: 68
    One way is to do a setback overnight and have all zones come on in the AM, that's if you have zones. You can setback the better insulated zones more, but remember as sludge says 150 water is not going to do what 170 water does so finely tuning your odr is critical.Bottom line is you need to add load, additional fin-tube, high-output might help. Some mod/cons have stepped offsets that modulate lower for longer hence forcing the output and getting some more condensing out of your cycle. Also if you don't have the fin-tube designed correctly you are in bad shape to start. Gotta do the heat load/loss first then boiler then fin-tube then odr.
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
    sludge said:

    aquastat temps are there for a reason... you lower them anymore then you won't move enough hot water to do the job. Common sense.

    That's true, but who's to say 180-160* supply temps are right… maybe their too high, maybe too low. And if he truly has a mod/con boiler, then there is no traditional aquastat. Water temps are handled by onboard controls and system sensors.

    @Hvac tech

    What boiler do you have? Does it have ODR and/or is it setup? Basically I stand by my previous statement, in that you can lower your supply temps as much as the building's heat loss will allow while maintaining your set indoor temps.

    By lowering the supply temps, you'll also lower the return temps indirectly. The lower the temps, the more efficient a mod/con boiler operates (generally speaking).
    Jean-David Beyer
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    As people often say here, It Depends.
    For example, I have a mod-con with outdoor reset. I have a fin-tube baseboard setup in one zone, and radiant slab in the other.

    For the baseboard zone, it runs with a supply of 120F until the outdoor temperature gets down to 50F. Then it rises to 150F when the outdoor temperature gets down to 0F. Design temperature around here is 14F, but it has gotten down to 0F twice so far this heating season.

    To run at these low temperatures, I replaced a three-foot piece of baseboard in each of the two rooms in that zone with 14-foot long pieces of baseboard. That is the width of the wall under the windows of those rooms. I wish I had put in enough baseboard to use the same temperatures (80F to 130F) that I use in my radiant slab. But that would have required turning corners for the baseboards.

    These temperatures are a little higher than when the system was first installed about 5 years ago. The winters have been colder than previously the last two years. It used to go down only to between 8F and 9F, and those only for an hour or two each night.

    Since I changed the temperatures, I have not had time to measure the temperature drops in the zones.
  • Hvac tech_2
    Hvac tech_2 Member Posts: 21
    It's a knight will have to add baseboard maybe a big old cast iron on the rreturn loop
  • remodel
    remodel Member Posts: 68
    Be careful, throwing CI in with fin-tube could be a problem. At this point the pencil and paper need to come out. Do you have a one-pipe system or two?