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A mod-con with existing baseboard retrofit Q....

AlexS Member Posts: 69
I didnt want to Hijack Steamfitters thread, though I have a similar situation.  The home I was at today has a boiler in the basement that has been flooded twice in two years.  First Irene, now Sandy.  Im pulling all the wood flooring on the first floor and suggested radiant instead of the existing baseboard.  They already have radiant under the tile in the kitchen.  The idea is to create a small utility room on the first floor and mount a Mod Con in there, so there's no more worries of flooding a boiler in the basement. 

The second floor bedrooms and large (vaulted) open area still have SlantFin baseboard which was sized for the 180 degree boiler....   I figure the lower temp water would just take longer to heat the upstairs so setbacks at night are no longer a smart idea, but what happens on a real design day?  That baseboard was designed for 180 degree water....

Is there a way to control it to run the upstairs zone at a higher temp for a period of time?


  • Paul48
    Paul48 Member Posts: 4,469

    I think the new Ultras can run 2 seperate heat curves.
  • Ironman
    Ironman Member Posts: 7,376

    So can the Knight and the new T.T.

    You'll have to install a mixing valve on each lower temp zone to limit the water temp when the high temp zone calls.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I think the new Ultras can run 2 seperate heat curves.

    They can. They could even run three reset curves if you do not use it for an indirect (I do).

    The controller provides for this.  It has 3 (on-off) thermostat inputs.

    I have 4 Taco 007 circulators.

    #1 feeds the indirect.

    #2 is the boiler circulator.

    #3 is the circulator for the radiant floor zone (downstairs on a slab)

    #4 runs the circulator for the baseboard zone (upstairs)

    For mine, Priority 1 (highest) runs the indirect, and gives it 175F water whenever the indirect feels chilly.  It controls circulator #1. In particular, circulators #2 and #3 are off.

    Priority 2 (middle) runs the radiant slab. It gives water between 76F and 120F depending on the outside temperature. It controls circulators #2 and #3. Circulator #1 is off.

    Since the controller controls only 3 circulators, I have added a Honeywell relay box. The box will switch on circulator #4 if the thermostat in that zone feels cold. An extra contact on that relay box calls for heat at Priority 3 (lowest). When that happens, the controller runs the baseboard zone. It gives water between 110F and 135F depending on the outdoor temperature. It controls circulator #2. Circulators #1 and #3 are off.

    The only thing to notice is that if the baseboard zone is calling for heat, its circulator (#4) runs, no matter what. If the Indirect is being run, it will not send hot water to the baseboard zone because the boiler circulator (#2) is not running. If the radiant slab zone is running , the baseboard will get warm water at the temperature required by the radiant slab. That is better than nothing; No point putting an extra relay to turn it off.

    The main problem is if both the radiant and baseboards want heat all the time. The controller divides up the time between them. This is to prevent an one zone from getting all the heat. For me, that is just fine because the baseboard does not require much heat. If both want heat, the radiant zone gets 30 minutes, the baseboard zone gets 20 minutes, etc. If after 2 hours the baseboard zone is not satisfied, the controller boosts the hot water 10F and tries that. If another 2 hours pass and the the baseboard zone is still not satisfied, it boosts the hot water another 10F. It stops boosting if the maximum temperature is exceeded (135F for me).
  • Gordy
    Gordy Member Posts: 9,546
    Like ironman said

    Plus I would opt for the fire tube hx offered with the knight, and tt. And ss verses ph sensitive aluminum block hx as with the wm.
  • AlexS
    AlexS Member Posts: 69
    thanks guys..

    What would be the point mixing down the lower temp zones and running a mod con at a higher output temperature... Seems it wont be in condensing mode at all, eliminating any savings. 

    I suppose it would be no different than the 85% unit in the basement currently, but would at least be upstairs so it doesnt get flooded again.

    They run an indirect as well, so would it be feasible to wire a zone controller to the DHW terminals on the boiler for both baseboard and potable water, and leave the new radiant wired to TT?
  • Paul48
    Paul48 Member Posts: 4,469
    edited November 2012

    appears that TT has done a poor job with prioritizing the 2 different reset curves at the boiler. The problem with using the DHW input for  it and the baseboards is, you lose the outdoor reset function. Some may disagree, but I'd rather use a relay to open the CH2(radiant) input, any time there is a call for DHW,or CH1(baseboard). You basically do what TT should have done.
  • CMadatMe
    CMadatMe Member Posts: 3,086

    Was a heat loss done to substantiate that the board footages meet the loss using 180 degree water? Would it not be better to replace existing residential board to high output or maybe SunTemo Synergy board?

    Could do a Viessmann Vitodens 200 with a Viessmann mixing package to give you two independent heating circuits that can be run on different curves and water temps.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
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