To get email notification when someone adds to a thread you're following, click on the star in the thread's header and it will turn yellow; click again to turn it off. To edit your profile, click on the gear.
The Wall has a powerful search engine that will go all the way back to 2002. Use "quotation marks" around multiple-word searches. RIGHT-CLICK on the results and choose Open Link In New Window so you'll be able to get back to your results. Happy searching!
In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Need to contact us? Visit

The right system circulator with a Viessmann WB2B 35

I have a Mono Flo single main system designed in the mid 50's that I am installing a WB2B 35 into. The original system has a 2" main that splits into two 1 1/4" branch mains. The branches are currently zoned with B&G 100 circulators installed on the returns which then tee back to a 2" return main. The branches are balanced with a pair of gate valves with thermometers located in front of The circulators.

The Viessmann is designed not to have zones and I do not need them. I am reworking my near boiler piping to Viessmanns System layout 2 using the Viessmann low loss header and recommended Grundfos boiler and DHW circulators. I am planing to do away with the B&G's and use a single system circulator on the 2" main supply.

My question concerns the system circulator. I have a calculated head loss of 4.8 ft and flow of 8.2 gpm @ a 25 deg delta. I am interested in using a Taco Bumblebee to maintain a constant delta t across the reset curve. My concerns are weather I should use a delta t circulator and with the varying flow will I be able to balance the system by throttling the existing gate valves or should I do it another way?

I have about 1800 sq ft of emitters with a design heat loss of about 109,000 BTUH so I only need about 125 deg for a design temp. We only hit the design temp here a few days a year so if I can hit a delta T of 25 Deg I should be condensing almost all of the time. I really don't care about anything beyond consistent comfort and economy so what ever circulator I need to do that with will be fine. I was just thinking that a variable speed pump would likely give me a nice consistent room temp across the reset curve. I have put a lot into calculating my head loss so I hope it is correct. Compensating for head loss is another atractive advantage of the Bumblebee. I also think it is cool that it displays the current flow.

As usual I would appreciate any thoughts you guys have and I do not mind learning I am wrong. That is how I got this far.




  • RichRich Member Posts: 2,129
    edited November 2013
    Bumble Bee

    The bumble bee should work just fine with your system requirements . Just watch your calculations and head  109,000 @ 25 Delta is 8.72 GPM if 100% water . If you increased the Delta to 35 that would put you right in the middle of the curve 2 & 3 for the Bumble Bee and would take you farther into the efficiency be it ever so slight . 

    Would using 2 Bumble Bees be out of the question ? Then both 1 1/4 circuits would remain as is , balancing would be at a minimum , considering whether it was balanced well to begin with and you would operate at 22 watts as opposed to 32 on design day . 1 at 32 or 2 at 44 and ultimate control .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC 732-751-1560
    Serving most of New Jersey , Eastern Pa .
    Consultation , Design & Installation
    Rich McGrath 732-581-3833
  • CanecreekCanecreek Member Posts: 21

    Thanks Rich,

    I have no problem using 2 circulators. I can connect both to the same terminals on the Viessmann pump control with no electrical load issues. I would need to install them on the 1 1/4" returns but do not see that as a problem with the expansion tank on the other side of the LLH. The two branches are similar. I was not thrilled with the idea of throttling one of the branches to get a good balance but was unsure about how well 2 circs would work together.
This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!