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

Multiple zone valves

chuck172 Member Posts: 90
I'm trying to calculate how many zone valves I can put through a 40va transformer.
If I take the zone valve motor amp rating and multiply by 24 volts, divide that total into 40, that's the answer (right)?
Now I'm looking at a honeywell zone valve and it reads the following:
24vac 50 va pilot duty
120vac 4.4 amps full load
28.4 amps lock rotor.
Which number do I use?


  • Which Honeywell

    zone valve are you using. The numbers you posted seem like relay numbers not Honeywell ZV's. If memory serves me Honeywell ZV's use about .2 amps so you can use 5 of them with a 40 VA transformer.

    If you are using a NEMA rated class II standard DC20-92 transformer you can exceed rating up to 200%.
  • chuck172
    chuck172 Member Posts: 90
    zone valve

    If a honeywell ZV drew .2 amps, .2X24=48
    Wouldnt I be able to use 8?

  • Tim

    Would you be so kind as to show me how you calculated that? Or tell me what I'm doing wrong. The .2 amps is a 5th of an amp; 24 volts divided by 5 is almost 5, so each zone valve is drawing 5 va; 40 va divided by 5 va is 8 zone valves. There's probably a de-rating in there somewhere?

  • Ken Sappio
    Ken Sappio Member Posts: 16
    Your Decimal is off

    .2 x 24 = 4.8 not 48

    So a 50 VA transformer should be able to handle...

    50 / 4.8 = 10.416 rounded to 10 zone valves
  • Honeywell in their

    literature for their zone valves states 5 ZV,s per 40 VA transformer.

    They also have a white paper they put out about 10 years ago that states that a 40 VA transformer can be run at 200% of capacity with only a small drop in voltage. This is how we can run three Taco ZV's with a 40 VA transformer as long as it is NEMA rated standard DC20-92 ClassII.For Taco which draws about 1 amp the math would be 1 x 24 = 24 VA per valve x 3 = 72 VA.

    With the Honeywell ZV's at .2 x24 = 4.8 divided into a 50 VA = 10.416666 so I would imagine 8 to 10 would be okay with a 50 VA.

This discussion has been closed.