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Siggy's thermal clutch C.I. boiler protection ala Cheep-skate

billyboy Member Posts: 152


This looks like an interesting way to protect C.I. boiler from low return water temps.

Then I checked out Taco's Variable Speed Setpoint pumps $$$

I think that it can be done like Siggy's Fig 3 diagram using a Tekmar 150 in PWM Cool Mode, sensor would be on boiler return.

As the Tekmar 150 don't have a "Demand" control, an added "Boiler Demand Relay" N/O points could be inserted in series with Terminal 4 output to the "Injection Pump" OR the 24VAC power to Tekmar could be cycled ON/OFF with "Boiler Demand"

A cheaper way or a "Bad Idea" ?


  • billyboy
    billyboy Member Posts: 152
    Thanks Hatt, I hadn't seen that "Caleffi ThermoMix" valve before.

    When I searched on Thermatic mix valves I missed it somehow.

    That is a simpler solution & I like it better.

    But, would my idea work?
  • billyboy
    billyboy Member Posts: 152
    Plan on boiler piped secondary/primary & hope to use a Taco 006 as boiler pump.

    The 1" ThermoMix valve has a CV = 10, I think that I could get 5+ GPM with about 35*F DT
  • billyboy
    billyboy Member Posts: 152
    Motive for piping this way is partly due to sketchy history of NG service in Crested Butte.

    If boiler or NG kraps out, I want to be able to keep pipes from freezing using the 22,500 BTU electric elements in the 50 gal. State Commercial Sandblaster water heater tank.

    This tank will normally be heated from the boiler via a FPHX but in an emergency heat can be put into system.

    Say the Winter low temps set the 1,000 yr record -50* or so, the 22,500 BTU's would be added to the boiler 85,000 BTU output.
  • Zman
    Zman Member Posts: 7,549
    That article is from 2004. There are tons of affordable new products out there to prevent condensing. Most tekmar controllers can do it internally. The taco I series mixers can solve the problem and provide outdoor reset.
    Do you have a drawing of what you are proposing?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 21,871
    There are a number of ways to provide boiler return protection, but you would be hard pressed to find a simpler, less expensive method than a 3 way thermostatic valve.

    Perhaps the very least expensive is a aqua stat with a bang, bang control. It turns the circ pump and on/off, on/off based on return temperature.

    Multiple pumps is a smooth way to accomplish protection, I'd guess the most expensive.

    I don't see how the piping shown in the Taco Viridian 2218 installation manual does not assure return protection and it uses 3 pumps? Even with the pump used as a bypass a cold slab could still overpower the ∆T bypass function?

    The only way that would work if you could shut down that boiler pump when the return is cold and the ∆T function enabled.

    This trainer shows 4 or 5 of the most common methods, with piping and component selection.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • billyboy
    billyboy Member Posts: 152
    see new thread:

    System Design #1 Crested Butte, Co