Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Buffer Tanks

servicetech Member Posts: 1
Hello - I have an application where two wall mount, low mass condensing boilers are serving a make up air ventilation unit with hydronic coil and a water coil unit heater used for space heating. The load for the makeup air unit is 254 Mbh and the unit heater is 60 Mbh. The primary system is configured with a dedicated boiler pump serving each modulating boiler. The secondary system, also a low mass system, houses the MUA unit and unit heater and is served with a single circulator.

My question focuses on the low mass application. I was planning on decoupling the boiler loop from the secondary loop with a low loss header. The boiler loop hold approx 20 Imp gallons and the secondary systems holds approx. 35 imp. gallons. Is the low loss header enough, or should a buffer tank in the secondary system be considered. Currently, the boilers can modulate to match Btuh demands of the mua unit and the unit heater?

Thanks in advance



  • CMadatMe
    CMadatMe Member Posts: 3,086

    What are the modulation rates of the boilers and will they be cascading? Whose mod/con are you using?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Brad White
    Brad White Member Posts: 2,393
    You can also

    combine the buffer tank with a hydronic separator, such as a Boiler Buddy. A large tank with large taps to do double-duty.

    I think what you are finding is that make-up air units and unit heaters, being low mass and with rapid transfer (moving air) require a relatively constant flow of water. With low mass boilers, this can lead to short-cycling when demands are sudden/immediate, so having a hydronic piggy-bank makes sense. That is, if I gather your application correctly.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • JohnNY
    JohnNY Member Posts: 3,152
    Hi, Brad.

    I'll tell ya'. I like that Boiler Buddy, but the one-year warranty scares me.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Plumbing in NYC or in NJ.
    Take his class.
  • Brad White
    Brad White Member Posts: 2,393
    Hey John!

    One year warranty?? I did not know that. Too bad. I wonder why that might be, so will ask HTP.

    I think instead of specifying a time-based warranty, I will just ask that the warranty be longer than one of Charlie Sheen's tantrums. :)

    Thanks, John- you got me thinking as usual.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
This discussion has been closed.