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Weil McLain 90 cv boiler

Snowmelt Member Posts: 1,295
This is more or less for hot hod & taco rep.
I am going to use taco sentry zone valves for a job, there three zones and an indirect. When I talked to Wales Darby the taco rep, they told me the 3/4 has more cv then the I inch, the problem is there is 1 zone, most like
Y the original zone in the home which is 1 1/4 piping but only 50,000 - 60,000 btu. The 3/4 zone valve can handle the flow. So could I just use a 3/4 sentry zone valve with reducers right at the valve to make sure the 2 - 4 feet per sec rule?
2 nd question the indirect water heater I want to repipe it. Right now it has a zone valve and a pump, I just think it needs a pump. I am going to use closely spaced tee for primary secondary and want to put the three zone and indirect on the secondary ( load side) Just to make it simplified, will that hurt the efficiency of the indirect? Any pictorial that I can see? I also goung to use a zone board taco zone board control. Any diagram will be helpful.


  • hot_rod
    hot_rod Member Posts: 15,064
    What size boiler? The one with the side tank and pump inside the cabinet?

    1) There are a bunch of online velocity calculators, here are a few examples.

    So a 3/4 ID pipe flowing around 6 gpm would be in the comfort range of 4 fps, so either valve is fine. Could be the 1" is less $$ after you add bell reducers to the 3/4 to increase to it to 1"?

    2) I'd rather see you pipe it with a hydraulic separator and take the indirect off a 3 way zone valve. Weil shows this in the multiple boiler piping diagrams in the manual. I've done some Knights this way. You get the hottest water to the indirect when you pipe directly to the boiler. Use a high Cv, 3 way zone valve. The Caleffi Z-one 3 way 1-1/4" size has a 7.5 Cv. The Zone Sentry 3 way is a low Cv, use a brand with at least a 7.5 if you are under 140K boiler size.

    Same 3 way ZV piping would apply if you pipe from a P/S, like Weil shows.

    Weil also shows how much extra capacity the onboard circulator has. Use an indirect with a large coil, low pressure drop.

    If you pipe the indirect from a secondary on a P/S or hydrosep, you get a blended temperature to it, and you need to run both circulators.

    Delta P circulator, Webstone Purge Ball at sep return purges all zones quickly, Sep 4 gives you separation, air, dirt, and magnetic separation to protect an ECM.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Snowmelt
    Snowmelt Member Posts: 1,295
    Yes it’s the one with the circ in the cabinet and the side tank, I already committed to not using a hydronic separator. How ever I might usewebstone brass ball valve purge tee For my primers secondary. I think I will just do this job the traditional way. Can I make my own p/s with black pipe using 2 inch pipe? Maybe 2 x 12 with some 2 inch cross tees .
    Oh it’s 150,000 btu but may be oversized.
  • hot_rod
    hot_rod Member Posts: 15,064

    Weil allows you to direct pipe that within the capacity of the onboard pump. They give you the spec and some examples, shown below.

    I'd still consider the indirect on a 3 way zone valve for the best recovery with only one circ running also, upper drawing in attached drawing. The lowest return to the boiler also, highest boiler efficiency

    Or it could be a secondary, may be slower recovery with lower SWT, and/ or the boiler may see a higher return, lower efficiency. It depends on the actual flow rates with both circs running. Generally there is some mixing going on at the closely spaced tees.

    Really no need to go larger that 1-1/4 pipe size for the loop on a 150. No sense in spending $$ on 2" for around 10 gpm of flow.

    If the indirect is a secondary probably 1" pipe will handle all that boiler can produce.

    Pressure activated bypass not needed if you use a delta P cir on a P/S, secondary loop.

    But use a PAB if you direct pipe to assure boiler flow with any
    zone operating.

    So you have 3 options
    Direct, as per Weils instruction & limitations.
    P/S with indirect connected to boiler loop via a 3 way ZV.
    P/S with the indirect as a secondary.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream