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Buffer Tanks again

Brad White_9
Brad White_9 Member Posts: 2,440
Open discussion everyone!

I am not familiar with a Quietside but assume it is a ModCon. All things being similar, let me stipulate that. By the way, an electric water heater is one of several forms a buffer tank can take. I personally like the HTP SuperStor line but there are others. The downside of EWH's is that the tappings may be limited in size and may limit flow somewhat. I like at least 1" tappings for even the smallest loads. HTP I am told makes a tank with 1.5" tappings but it must be special order. Anyway, on to application.

Here are my thoughts and approach:

1) If you were to install the buffer tank on the supply side (outlet of boiler but before the secondary load), you potentially might have to "wait" for your heat. You would have to deplete all of that cold water before your radiation (in whatever form) got something useful to work with.

2) I prefer to put the tank on the return so that the radiation sees the water it needs right away. When the return water starts to climb over a certain temperature, the warmer return water is "banked" for later use.

3)The way I do it personally -and it is not perfect- is I use a HWR aquastat to operate a parallel circulator. When the HWR temperature rises, the HWR is diverted to the tank in an on-line/off-line setup. When the HWR temperature again drops, the tank water depletes, allowing a "coasting" effect between cycles. My tank is a 30 gallon S-S by the way, coupled to a non-modulating but condensing Monitor MZ of 94 MBH input. House heating load is about 48 MBH...

Next time I do this I will just use a main valve between two tees and close it to divert flow rather than running a circulator. I did mine in haste and frustration.

4) The way YOU might do it may be similar or vary greatly. Personally the on-line/off-line approach can serve you well.

5) There may be a way to do the same arrangement but on the supply side. I will have to think about that more. I see a diversion to charge the tank happening when the boiler Delta-T has narrowed, indicating approach of load satisfaction.

6) Keep in mind that the buffer tank temperature can vary greatly. You want to size your tank and target temperatures for the average tank temperature versus the radiation load at that time, if that makes sense. In other words, your tank may have a 130 degree high temperature and a 110 degree low temperature, so a 120 degree average. Compare that to what the radiation needs at such low-load times. The good news is, the whole idea of buffer tanks is for low-load times with potentially higher OD temperatures anyway.

Hope this helps a bit.


  • Rob Blair
    Rob Blair Member Posts: 227
    Buffer tank location again

    Looking at redoing a job where the original installer used a Quietside QVM9 090, which modulates down to 46K input. The heating load is 9000 and the thing is short cycling. Quietside makes a buffer tank but I was told to use an electric water heater as a less expensive option. If so, where would you pipe it in the primary loop? The Quietside rep said before the takeoffs to the secondaries, so I guess that means upstream of the secondaries? Is this a good idea (Electric water heater) or should I just go with the Quietside Buffer tank?

    BTW, I attached a picture of the current job.


  • proceed cautiously

    Looks like the 'communicating' thermostat is mounted next to the boiler so that extra zones could be incorporated. If so, it can't sense what's happening in the zones' conditioned spaces and may be set to run full-bore - in other words - not modulating at all.

    Check the venting very carefully. You may be outside the limits per the mfgrs lit.
  • Kal Row
    Kal Row Member Posts: 1,519
    you can try this...

  • Kal Row
    Kal Row Member Posts: 1,519
    this worked for me, see pdf

This discussion has been closed.


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