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Benefit of zoning with outdoor reset on MOD CON

TPell Member Posts: 1
Greetings all,

1st post here.


 I own an 2500sq ft poorly insulated 1850s greek revival in New Haven Ct. Last year we upgraded out boiler from an oil fired Weil McClain to a Burnham Alpine 150.  Its set up with an indirect fire triangle tube DHWH on 1 zone and the rest of the house is heated on 1 MASSIVE zone. Thermostat is on 1st floor in the den on a wall that is in the middle of the house. Both zones are being run with grundfos 3 speed circulator pumps. I leave the thermostat @ 65F all the time. Really significant savings are already being realized, but the piping to each radiator was left as is to save on installation costs with plans to repipe in the near future.

What I want to do:

It looks like in the past the system was set up as a gravity piping system. The pipes get progressively larger "up to 4" CI pipes before they come back to the primary loop around my boiler. Luckily all the connections between pipes are in the basement. What I want to do is break the connections where multiple radiators are running off 1 pipe, build a manifold system and run home runs to each cast iron radiator from the basement. and create a seperate zone for the 1st and second floors. Bedrooms on 2nd floors, living space on 1st.

The question:

Will zoning the system will really save any money on my monthly gas bill when using the outdoor reset? I envision being able to set the 1st floor temp back a few degrees at night and 2nd floor back during the day. I've read that setting back the thermostat is counter productive with mod cons and ODR because it will cause the water temp to drop to the point where the boiler will have to refire back up to 100% when it could cruise @ around 20-40% like it does now when it gets to set point temp.

Any thoughts will help. I plan on repiping the basement for head room purposes with way, just wondering if it makes sense to go through the extra effort and cost of buying manifolds, an extra pump, relay, and tstat.




  • SWEI
    SWEI Member Posts: 7,356
    Zoning and Setbacks

    The value of setbacks is questionable on most radiant systems, even more so those with high mass in the system (like your old gravity system.)  Small ones (perhaps 2-4ºF) can work OK.

    In my book, a more proper use for zoning (and thermostats) in a modern hydronic heating systems are as a method of dealing with external heat sources and infrequently occupied rooms.  In the former, a theromstat is placed in and controls a room having a woodstove or significant solar gain, to prevent that room from overheating during a time when the rest of the house still requires heat.  In the latter, a guest room or wing, a shop, or other space which is used infrequently is left at a lower temperature most of the time, but can be warmed up on several hours' notice when needed.
  • Bob Bona_4
    Bob Bona_4 Member Posts: 2,083
    if anything

    Doing a manifold system zoned is going to give you more control over first/second floor comfort. A worthwhile project in my book and can only give you more savings in fuel.. A primo setup would be pex-al-pex home runs to the rads. Then. ..ecm pumps to the manifolds and thermostatic valves in place of existing rad valves for room to room control.

    Plus you'll gain that headroom.
  • gennady
    gennady Member Posts: 839

    Zoning and setbacks are not working well in systems with outdoor reset. You can either install TRVs on each radiator or do outdoor reset for each zone.
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