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

taco Sentry

Snowmelt Member Posts: 1,387
I was at a customers home wanting the boiler re-piped, the existing zone valves weren't in one area, in fact one zone valve was 15 feet away from the boiler. When the boiler was replaced the contractor didn't update any of the boiler near boiler piping, still has an old air scoop and original zone valves. I am going to replace the air scoop with the taco 4900. The old zone valves are white rogers, I want to replace them with the zone sentry valves. The sales rep told me the 3/4 cv is greater then the 1 inch ( the 3/4 is 10.3 and the one inch is 8.7) with that being said, why use the 1 inch and not just use the 3/4 and on the end of the zone valves just install 3/4 to one inch adapter.


  • GroundUp
    GroundUp Member Posts: 1,573
    Is 8.7 not enough?
  • hot_rod
    hot_rod Member Posts: 19,282
    7 gpm is about 4 fps velocity in a 3/4" tube, that is about the max you would want to flow, to keep it quiet and troublefree.

    7 gpm thru a 10.3 Cv valve is .46 psi pressure drop.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Snowmelt
    Snowmelt Member Posts: 1,387
    That one zone ( main house is 1 1/4 piping) but I’m almost positive it’s over sized pipe so if the zone with the 1 1/4 piping is only 80,000 btu or closer to an even 100,000 btu could I just use the 3/4 inch sentry valve and a one inch to 3/4 reducer and squeeze the 100,000 btu thru the zone valve?
  • newagedawn
    newagedawn Member Posts: 586
    no, not a good piping practice but its your life
    "The bitter taste of a poor install lasts far longer than the JOY of the lowest price"
  • Zman
    Zman Member Posts: 7,447
    edited July 2018
    Sizing the valve to the designed flow rate and resistance is the right way to do it. If you had an old 3" gravity pipe, you sure wouldn't go find a 3" valve for the application.
    I would absolutely stay under 4 ft/sec if the valve is in an area where velocity noise will be a problem. If it is just going in a boiler room, 6 ft/sec is OK as long as it is within the manufactures recommendation.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • hot_rod
    hot_rod Member Posts: 19,282
    I agree with Zman , any/ all valves should be sized by the intended flow rate and acceptable pressure drop. Notice that valves are often available with various Cv ratings. We build 3/4 spring return zone valves in 2.5, 3.5, 5 and 7.5 Cv.

    Be especially careful with check valves and flow checks, their Cv rating is in the full open position. If you oversize, the flapper or disc inside is floating around somewhere between full open and full close position. Noise, wear, and additional pressure drop is the result.

    While it may look odd you may see a 1-1/4 check valve on a 2' pipe for example, that is fine if it was sized properly to the actual flow rate.

    Check valve sizing is becoming even more critical with variable speed pumping. Use a check designed for hydronics so they pop open and are friendly to flow in partial open positions.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream