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How to operate boiler controls

I have an 80-year old house that was converted from steam to hot water.  I am renovating the entire house and removed all existing piping (some as large as 6") and will replace with appropriately sized copper pipe set up in 3 zones.  I will not use zone valves since I will have TRVs on each radiator, so the zones will just provide flexibility if work is needed and allow me to isolate sections of the house.  I also removed some cast iron radiators and replaced with Myson Select radiators.  The previous radiators were oversized and the Myson's saved on space.

I am going to install TRV's on all radiators and go without a thermostat.  I also plan to run the circulator continuously.  My question is how to set the temperatures on the boiler.  I have an old Peerless that runs on natural gas.  I don't have the numbers in front of me, but the output is in the 250k BTU range, but since I've insulated and installed new windows I surely don't need this big of a boiler anymore.  I will replace in the future but want to at least get through this winter (I'm in Chicago).

Knowing that I will run the circulator continuously, will install TRV's on all radiators and will not have a main/room thermostat I am thinking of installing a  triple aquastat, but I am not sure of the settings (I do have a bypass installed to cover when the TRVs begin to close).

Can someone please suggest the correct settings on the aquastat along with any other issues I need to worry about?  I am also wondering if it would be worth it to install and outdoor reset.

Thanks - Tim


  • Tim McElwain
    Tim McElwain Member Posts: 4,506
    Do a heat loss on the house

    if you find the boiler is over sized then run it at a lower temperature on the low limit around 170 with the high limit set at 190. With outdoor reset that temperature with constant circulation and TRV's will give you nice comfort and economy at the same time. Too bad you are not replacing the boiler with a Mod/Con boiler as your set up is ideal for low return water temps with outdoor reset and condensing on the boiler.
  • aardvark90
    aardvark90 Member Posts: 2
    Follow up

    Thanks for replying McElwain, I appreciate the input and will look to set it up as you've suggested.  I now need to figure out the best reset control to use.  Would it be possible to use a Honeywell AQ475A and jumper the thermostat input to represent a constant call for heat (I have TRVs installed)?  I can then let the AQ475A take over and establish that water temp though I would look to establish a minimum temp of something like 140 degrees (I don't have a DHW loop at this time).  

    I will be swapping out the boiler in the next year or two and was hoping to set it up for the future.  Given the recent updates I will also look to have a heat loss calculation performed so I can be sure the new system is properly sized.

This discussion has been closed.