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Buffer tanks with condensing boilers / combi boilers

bob eck
bob eck Member Posts: 922
Hello I hope and 🙏🏻 everyone is staying healthy during this COVID-19 crisis

When installing condensing boilers or condensing combi boilers are you installing buffer tanks on these installations?
If you are what brand buffer tank are you using?
When installing the buffer tank are you also installing a air eliminator or are you installing something similar to the Spirotop on the top of the buffer tank?
Any buffer tanks made with a magnet 🧲 inside to help collect the magnetic parts in the water? The magnet would be in a well in the side of the tank.

Stay safe and healthy.

Comments

  • clammy
    clammy Member Posts: 2,637
    On my own jobs what makes me use a buffer tank on mods vary according to the boilers lowest modulation in comparison to the smallest zone load, with that being said on some mod con u can de rate the central heating output but also use the ramp delay to prevent short cycling. In some cases I ll combine-small zones and balance them out to make the load larger. If there set on micro zoning then I’ll install a buffer . There few times I have I tend to use boiler buddy ,pipe my boiler in one side n load on the other if I’m concerned about water and iron oxide I’ll add a magnetic separator on the return side in the boiler protecting the heat exchanger and if using a ecm pump then one on the system return . I know some will options on buffers but I kinda like the boiler buddy being it does a few things and is tall and narrow leading to good temp stratification instead of a bleeding. The location of the tank well for a system sensor is not recommend by myself being it really should be up higher so when using a system sensor I’ll mount it on my either the system pump inlet or it’s outlet . Personally I would do the math and get rid of ultra micro zoning use a boiler that sized correctly and not oversized and a boiler w a hi turn down 10-1 ,if not using a boiler buddy I would still use a hydro separator for your ps piping ,less time ,less distance to ensure proper mixing and I feel better strata faction / td across system s and r as opposed to 2 tee my opinion. they both cost more then two tees and I think the price between a boiler buddy and say a califee hydro separator is not a big difference it also depends how much room also. I ve had great luck w panel rads trv s and using a boiler buddy on constant circ based on outside temp .the boiler is cycled by a t stat works wonderful zero short cycling even though lowest mod on boiler is larger then smallest zone no issue .hope this all helps your decision . Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • hot_rod
    hot_rod Member Posts: 14,552
    There are a handful of nice, hydronic specific buffer tanks available now. Choose between plain steel, glass lined, stainless or composite. pros and cons to each.

    I prefer a micro bubble type air eliminator with any mod con or high efficiency boiler. We want fire against metal, water against metal on the other side, not micro air bubbles and pockets.

    To leverage the stratification layering in the tank, and to leverage draw down via ORD, the sensor up top in the tank is best.

    Good idea about a magnet in the tank, Caleffi has a brass dry well magnet that would screw into one of the lower connection ports, like maybe an electric HW tank element hole.

    Suppose your smallest zone exactly matched then lowest turndown, call it 8,000 BTU/ hr. Would a buffer still have any value?

    Look at data like this for hours of occurrence, notice how many days you are below design conditions. That 8K load could be much lower for much of the heating season, so still some value, if reducing cycling is the main goal.

    How many zones are too many? I think one of the key advantages to hydronics over FA is the ability to give a building owner as much temperature control as they can handle :)

    Why maintain unused rooms at "living" temperatures? Allow folks to turn down bedroom temperatures at night if they enjoy cooler room temperatures.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • PerryHolzman
    PerryHolzman Member Posts: 234
    I've been following the conversations on buffer tanks for mod/con boilers for a while out of interest.

    I was thinking about my system and how it might affect things... I doubt it would make any difference.

    I have cast iron baseboard heating (on a monoflow T loop). The high thermal mass of the cast iron is my "thermal buffer" to minimize boiler cycling in low heat modes.

    Yes it does cycle in the fall and the spring. Otherwise it constantly fires during the coldest parts of the winter matching heat load.

    Just running the mental math in my head I cannot see where a buffer tank helps any heating system that has a large thermal mass (cast iron radiators, concrete heated floors).

    I can see it if you have just copper tube/air-fin (or similar) low mass radiators.

    I'd appreciate comments for my education on this.

    Perry
  • hot_rod
    hot_rod Member Posts: 14,552

    I've been following the conversations on buffer tanks for mod/con boilers for a while out of interest.

    I was thinking about my system and how it might affect things... I doubt it would make any difference.

    I have cast iron baseboard heating (on a monoflow T loop). The high thermal mass of the cast iron is my "thermal buffer" to minimize boiler cycling in low heat modes.

    Yes it does cycle in the fall and the spring. Otherwise it constantly fires during the coldest parts of the winter matching heat load.

    Just running the mental math in my head I cannot see where a buffer tank helps any heating system that has a large thermal mass (cast iron radiators, concrete heated floors).

    I can see it if you have just copper tube/air-fin (or similar) low mass radiators.

    I'd appreciate comments for my education on this.

    Perry

    Your thinking is sound in that your high mass baseboards are plenty of mass or "flywheel" with your boiler turndown.

    Buffering is more value in zoned, or micro-zoned systems where the load is a small fraction of the boiler output frequently. Also where systems are at partial load often, combined with micro loads.

    That being said for years we got by with single speed boilers, cast type addd enough mass to mask short cycles. Small size modulating boilers was a huge step forward for hydronics.

    Low mass, low water content copper tube boilers on zoned systems, well that's another story. I've watched them cycle multiple times a minute all season long :(

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
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