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Help designing constant circulation with CI radiatiors and low mass boiler

BBrosBBros Member Posts: 2

I'm in the trades and have a "reasonable" knowledge of heating systems, but need some help with specifics for a house I'm remodeling. The local heating contractors do not have much experience with the type of system I'm interested in, such as has been discussed on this site.

Home is 1920's two-story in Central Maine. Total heat-loss is around 62k btu, the largest space being kitchen/family room at 16.6k loss. Emitters are all original CI radiators, mostly 2x over-sized (i.e. bedrooms have 4.5k btu loss with over 8k in emitter capability).

I'm planning to home-run with 1/2 pex to a radiant style manifold. Boiler is Purepro Trio low-mass oil fired at 79k net IBR (smallest model). I have a hydrostat with outdoor reset capability. My intent is to have a single variable speed circulator and TRVs.

So... which circulator, which TRVs, and what else is necessary? My calculations say 145F water and perhaps only 1gpm, which seems really low. Do I need to worry about protecting the boiler from condensing, and if so, through what method.

DHW is planned to be on a separate system, but if it would be better to do a indirect to keep the mass up, I'll consider it. Do I need a pressure bypass in the system? Should it be primary-secondary? Hydronic separator?

I've read so many threads on here about various systems, and I understand most of it, but some specific layout/equipment info is still needed. My heating contractor is comfortable building whatever I want, but as noted, doesn't have familiarity with this type of system (constant circ, TRVs).

Thanks for any guidance.


  • GordyGordy Member Posts: 5,482 ✭✭✭✭✭
    I See

    A Taco I Valve with outdoor reset, and boiler protection. Yes you have to keep return temps to boiler above 130.

    You say you have reset capability on the boiler , but not whether you have the components for ODR. Primary secondary Piping, or Hydraulic seperator. Delta P circulator on radiation side of an eco vario circ, or bumble Bee variety for the TRV's after seeing what system head is if those circs will work. They should.

    If you are over radiated thats great for modulating water temps. To bad its not a Modulating boiler, but I take it oil is only available fuel source.
  • BBrosBBros Member Posts: 2
    Primary Secondary


    I have the Aquastat 3250 w/the ODR kit. How does the Taco I Valve fit into the equation? As a replacement? Does it work in conjunction?

    If using primary/secondary there will be just a standard fair circulator on the prime loop, and the variable on the secondary (sized for the head of the system). That would mean no pressure relief is necessary, correct? Or should one be on the end of the manifold so that in the event all the TRVs are closed, that it has room to flow as the pump slows down. I don't know why I envisioned a single circulator system. Not really possible.

    Anyone have TRV recommendations? There seem to be quite a number of options, and variances in cost.

    Indeed, oil is the only option. NG is years away and is increasing in price dramatically where available. LP is an option, but the efficiency of the mod-con wouldn't over come the added expense of fuel. Coal and wood options are not appropriate for this application.
  • GordyGordy Member Posts: 5,482 ✭✭✭✭✭
    edited August 2014

    The I valve R has reset capability you have that. The S series has setpoint capability. So S Series for boiler protection it has a boiler return sensor, and supply sensor.

    Delta T circ would do the job on the emitter side also probably better even than delta P. Set the delta for 20* and the circ will change speed to maintain set delta as trvs close, and higher flow rates start to happen. The Bumble bees curve may not meet the system flow rates, and head though.

    TRVs Danfoss, Caleffi make nice ones.

    Think about boiler cycling, and buffer tank.
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