How to set boiler controls


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Old 09-29-09, 12:54 PM
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How to set 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
 
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Old 09-29-09, 02:38 PM
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We'll wait for others to chime in but I would not maintain water temp in a boiler.
 
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Old 09-29-09, 04:20 PM
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With all that potential to use low water temperatures in the distribution system, you might consider primary/secondary piping with variable speed injection and outdoor reset, and constant circulation with an ECM pump (e.g., Wilo ECO or Grundfos Alpha) on the distribution side.

The good news is going this route now would set you up in the future for a new gas modulating condensing boiler. A well-thought out piping layout would make it pretty simple to swap out the boiler in the future. The controls suggested above would be overkill for a short-term fix prior to new boiler, though. But you could also do something somewhat simpler.
 
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Old 09-29-09, 04:55 PM
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Thanks for the feedback xiphias. I am trying to keep things simple right now, but I like the idea for the long term. Since the new boiler will be much smaller I will have plenty of space to pipe it correctly. Under the suggested scenario I assume the primary circulator would run continuously, but how would I get the secondary circulator to come on?

rbeck - since I won't have a thermostat if I don't maintain a certain minimum temp. what will kick the burner on when the system needs heat?

Thanks - Tim
 
 

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