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AquaSmart on conventional gas boiler

Thank you for all of the info, I've done some additional reading and educated myself on boilers.  I'd like to start over and approach this setup systematically:

Existing System:

I have a 100yr old victorian home near Chicago that is ~2000 sq ft.  Out winter gas bills are usually no more than $170/mo.  It was originally heated by a gravity fed steam system and a coal boiler which is all still in the basement.  The current boiler was added in ~1990 and was spliced into the existing coal boiler input & outputs (I know, not ideal!).  The current boiler is a 112,000 BTU sold through Carrier, but I am unsure of the mfg that made it.  It has a certification sticker by Dunkirk on the side which is conveniently covered up by the on-off switch.  I could pull that off if it had any relevant info on the side of it if necessary.  Previously there was an analog thermostat and a Honeywell L8148E Aquastat which had a high limit of 180F, I'm not sure if it had a Low limit.  There is no Domestic Hot Water or a bypass loop that I am aware of.  There is a Effikal flue damper (RVGP-KS-6-BKF) which was wired into the aquastat and operated well. 

In the past the thermostat would call for heat and the boiler & circulator would come on and start heating/circulating the water to the cast iron radiators in the house.  Once the call for heat was satisified the boiler and circulator would shut down and cool until the thermostat initiated a new call for heat and would repeat the sequence.  I don't recall the boiler short cycling or shutting off from hitting the high limit.  We would have the boiler cleaned every year for the 5 years we have owned the house and haven't had any issues.

Recent Changes:

I have recently installed a programmable thermostat and the Beckett Aquasmart controller and have some questions about setting up the Aquasmart system.  My current settings on the Aquasmart are as follows:

Hi Limit - 180F

Hi Differential - 20F

Lo Limit - 130F

Lo Differential - 10F

Circulator OFF - Set to allow boiler to run for 4min prior to circulating the water to the radiators

Circulator ON - Set to allow circulator to run for 4min after boiler has shut off to keep circulating the water to the system and put the heat into the rooms

Heat Manager is set to - HIGH Efficiency to let the controller maximize the efficiency of the system.


It appears that my boiler was running as a "cold-start" boiler for at least the 5 years we have owned the home.  If we continue to keep current on our yearly cleanings, is there any reason to not continue this?  Does the flue damper help this out?

I feel like our boiler will fire often to keep itself warm in our unheated/finished basement that is usually ~50F during the winter with a Low limit of 130F.

I'm not sure how to regulate the return water temps so that they are over 130F when the boiler fires up to minimize condensation. 


  • Ironman
    Ironman Member Posts: 7,373
    edited January 2013

    I hate to tell you this but, a converted gravity system has a sort of natural reset built into it because of the high mass of the c.i. rads and the large volume of water which acts as a buffer. You do Not want to use set back on this type of system. It will only cause it to take longer to recover and sacrifice comfort with no energy savings.

    A $170 a month gas bill for your house plus a c.i. boiler is about as good as it gets. Unless of course, you were to super-insulate and thoroughly seal up the envelope. Insulating your piping in any cool or unconditioned spaces would be your best low cost improvement.

    Thus, both the components you've added will probably be of little or no benefit as far as saving fuel. The low limit setup is for a boiler with a tankless coil. You boiler should be setup for cold start. While there is some advantage on an oil boiler to use warm start, there is none with gas as a rule.

    If low return temp or sustained flue gas condensation is an issue, then a bypass would be the simplest solution.

    The boiler is made by Dunkirk for Carrier.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • ChadZeilenga
    ChadZeilenga Member Posts: 12
    Thanks Bob

    Hi Bob,

    Thanks for the info.  My old Aquastat went out, so for a small cost increase I opted for the Aquasmart ($160).  After information I had read online I only recently put in the Lo limit setting at 130F as I was seeing a lot of issues with low return water temp and leaks developing in boilers and condensation. 

    Previously I was operating with no low limit at all and letting the AquaSmart determine the required high limit based on my demand.  It's pretty "smart"!

    The low return temp and condensation are two of my concerns and I'm trying to figure out what would be optimal.  I believe the system operated as a cold-start for 20 years without any issues and nothing has been brought up during my cleanings, so I was curious if I could continue to do that.
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