Recommendation 3; SUPPLY ; RETURN - Page 7

Recommendation 3

 is used when the return water temperature goes below 135°F for prolonged periods of 

time. This is also primary-secondary piping, but includes the addition of a 3-way valve, return water sensor and 
boiler-mounted RTC Return Temperature Control.

 RETURN PIPING SIZE (IN)

SUPPLY 

RETURN 

RETURN 

PIPING 

HEADER 

BRANCH 

SIZE (IN) (1) 

RETURN (2) 

(2A) 

(QTY.) SIZE (2B)

  BOILER 

20°F 

40°F 

20°F 

40°F 

20°F 

20°F 

   MODEL 

DROP 

DROP 

DROP 

DROP 

DROP 

DROP

24-03 

2 

1-1/2 

2 

1-1/2 

– 

– 

24-04 

2 

1-1/2 

2 

1-1/2 

– 

–

24-05 

2 

1-1/2 

2 

1-1/2 

– 

–

24-06 

2-1/2 

1-1/2 

2-1/2 

1-1/2 

– 

–

24-07 

2-1/2 

2 

2-1/2 

2 

– 

–

24-08 

2-1/2 

2 

2-1/2 

2 

– 

–

24-09 

3 

2 

3 

2 

– 

–

24-10 

3 

2-1/2 

3 

2-1/2 

– 

–

24-11 

3 

2-1/2 

3 

2-1/2 

– 

–

24-12 

4 

2-1/2 

4 

2-1/2 

3 

(2) 3

Notes:

1.  All piping is schedule 40.
2.  Pipe sizes listed are based on a 20° F or 40°F differential (temperature drop).  

Select one to match application.

3.  When specified return piping is less than  3”, install 3” x 12” nipple and appropriate  

size bell reducer directly into boiler return tapping as shown.

4.  Drain valve—ball valve preferable, gate valve acceptable alternative  

(supplied by others).—Minimum valve size per ASME code is 3/4” NPT.

5.  Maximum linear feet of pipe from 3-way bypass port to sensor location = 11 feet.   

Bypass line shall be the same diameter as return A.

6.  Minimum linear feet of pipe from point of mixing (where bypass meets return line)  

to sensor location = 4 feet.

7.  Install special 3” x 12” nipple with 1/4” NPT side tapping closest to boiler.   

Where applicable, use bell reducer to adapt to recommended return pipe size.

8.  Proper boiler circulator sizing is listed in RTC literature.

24-03 THRU 24-11 (W/20°F DROP)
24-03 THRU 24-12 (W/40°F DROP)

24-12 (W/20°F DROP)

BOILER CIRCULATOR

(BY OTHERS - SEE NOTE 5)

DRAIN VALVE

(SEE NOTE 4)

SUPPLY

DIVERTING

VALVE & ACTUATOR

SUPPLY

1

BOILER CIRCULATOR

(BY OTHERS - SEE NOTE 5)

DRAIN VALVE

(SEE NOTE 4)

SUPPLY

1

1

3

DIVERTING

VALVE & ACTUATOR

3

2

2

SYSTEM

PUMP

CLOSELY
SPACED

TEES

D

MAX

4D

REAR OF 

BOILER

REAR OF 

BOILER

RETURN

RETURN

RETURN

 SENSOR

 (SEE NOTE 7)

RETURN

 SENSOR

(SEE NOTE 7)

3” x 12” NIPPLE

AND BELL REDUCER

(SEE NOTE 4)

SEE NOTE 6

SEE NOTE 5

SUPPLY

1

2B

2A

RETURN BRANCH

SYSTEM

PUMP

CLOSELY
SPACED

TEES

D

MAX

4D

2

2

RETURN

RETURN HEADER

RETURN

SEE NOTE 6

SEE NOTE 5

24-03 THRU 24-11 (W/20°F DROP)
24-03 THRU 24-12 (W/40°F DROP)

24-12 (W/20°F DROP)

BOILER CIRCULATOR

(BY OTHERS - SEE NOTE 5)

DRAIN VALVE

(SEE NOTE 4)

SUPPLY

DIVERTING

VALVE & ACTUATOR

SUPPLY

1

BOILER CIRCULATOR

(BY OTHERS - SEE NOTE 5)

DRAIN VALVE

(SEE NOTE 4)

SUPPLY

1

1

3

DIVERTING

VALVE & ACTUATOR

3

2

2

SYSTEM

PUMP

CLOSELY
SPACED

TEES

D

MAX

4D

REAR OF 

BOILER

REAR OF 

BOILER

RETURN

RETURN

RETURN

 SENSOR

 (SEE NOTE 7)

RETURN

 SENSOR

(SEE NOTE 7)

3” x 12” NIPPLE

AND BELL REDUCER

(SEE NOTE 4)

SEE NOTE 6

SEE NOTE 5

SUPPLY

1

2B

2A

RETURN BRANCH

SYSTEM

PUMP

CLOSELY
SPACED

TEES

D

MAX

4D

2

2

RETURN

RETURN HEADER

RETURN

SEE NOTE 6

SEE NOTE 5

Series 24 Minimum Piping Recommendations – Steam Boiler

Notes:

1. All piping is schedule 40.
2.  To prevent condensate from being trapped in header, do not reduce equalizer elbow at header 

connection.

3.  Drain/blowoff valve—ball valve preferable, gate valve acceptable alternative (supplied by others).

•  Mininim valve size per ASME code is 3/4” NPT 24-03/24-05; 1” NPT 24-06/24-10;  

1-1/4” NPT 24-11/24-12.

• Increasing the valve size will improve the blowdown operation
•  In all cases, piping connection blowoff valve to boiler should be full size to the point of discharge.

4.  For pumped return systems, see Series 24 installation manual. 

RISER  

PIPING SIZE (IN) 

SPACING (IN)

RISER 

HEADER 

  BOILER 

(QTY.)  

& SUPPLY  RETURN 

EQUALIZER 

   MODEL 

SIZE (1)  

(2)  

(3) 

(4) 

‘A’ 

‘B’

  24-03 

(1) 3” 

3” 

1-1/2” 

2” 

– 

–

  24-04 

(1) 4” 

4” 

2” 

2” 

– 

–

  24-05 

(1) 4” 

4” 

2” 

2” 

– 

–

  24-06 

(1) 4” 

4” 

2-1/2” 

2-1/2” 

– 

–

  24-07 

(2) 4” 

6” 

2-1/2” 

2-1/2” 

36” 

–

  24-08 

(2) 4” 

6” 

2-1/2” 

2-1/2” 

42” 

–

  24-09 

(2) 4” 

6” 

2-1/2” 

2-1/2” 

48” 

–

  24-10 

(2) 4” 

6” 

3” 

3” 

54” 

–

  24-11 

(2) 4” 

6” 

3” 

3” 

60” 

–

  24-12 

(3) 4” 

6” 

3” 

3” 

30” 

36” 

24-07 THRU 24-11

24-12

24-03 THRU 24-06

(SEE NOTE 4)

(SEE NOTE 4)

(SEE NOTE 5)

(SEE NOTE 5)

(SEE NOTE 5)

(SEE NOTE 3)

SEE NOTE 2

(SEE NOTE 3)

RISER

WATER LINE

EQUALIZER

CLOSE NIPPLE

24” MIN.

18” MIN.

HARTFORD LOOP

(REQ’D ON GRAVITY

RETURN SYSTEM)

REAR OF BOILER

BLOW-OFF/

DRAIN VALVE

(SEE NOTE 3)

DRAIN VALVE

(WET RETURN)

2” TO 4”

SUPPLY

1

1

1

3

3

4

4

4

3

2

2

2

2

2

2

‘A’

‘A’

‘B’

RETURN

HEADER

(SEE NOTE 4)

24-07 THRU 24-11

24-12

24-03 THRU 24-06

(SEE NOTE 4)

(SEE NOTE 4)

(SEE NOTE 5)

(SEE NOTE 5)

(SEE NOTE 5)

(SEE NOTE 3)

SEE NOTE 2

(SEE NOTE 3)

RISER

WATER LINE

EQUALIZER

CLOSE NIPPLE

24” MIN.

18” MIN.

HARTFORD LOOP

(REQ’D ON GRAVITY

RETURN SYSTEM)

REAR OF BOILER

BLOW-OFF/

DRAIN VALVE

(SEE NOTE 3)

DRAIN VALVE

(WET RETURN)

2” TO 4”

SUPPLY

1

1

1

3

3

4

4

4

3

2

2

2

2

2

2

‘A’

‘A’

‘B’

RETURN

HEADER

(SEE NOTE 4)

24-07 THRU 24-11

24-12

24-03 THRU 24-06

(SEE NOTE 4)

(SEE NOTE 4)

(SEE NOTE 5)

(SEE NOTE 5)

(SEE NOTE 5)

(SEE NOTE 3)

SEE NOTE 2

(SEE NOTE 3)

RISER

WATER LINE

EQUALIZER

CLOSE NIPPLE

24” MIN.

18” MIN.

HARTFORD LOOP

(REQ’D ON GRAVITY

RETURN SYSTEM)

REAR OF BOILER

BLOW-OFF/

DRAIN VALVE

(SEE NOTE 3)

DRAIN VALVE

(WET RETURN)

2” TO 4”

SUPPLY

1

1

1

3

3

4

4

4

3

2

2

2

2

2

2

‘A’

‘A’

‘B’

RETURN

HEADER

(SEE NOTE 4)

PIPE SIZING AND NOTES FOR RECOMMENDATION 3