Boiler Feed Pump Calculator 鈥?Free Online Sizing Tool

Q: How do I size a boiler feed pump?

Three steps: calculate flow rate from boiler capacity, calculate TDH from system pressure and friction, then size motor power from flow x head x specific gravity / efficiency.

Q: What is the difference between 1W1S and 2W1S?

1W1S: 1 working + 1 standby, each 100%. 2W1S: 2 working + 1 standby, each 50%. 2W1S offers better part-load efficiency.

Q: What pump efficiency should I use?

Centrifugal pump: 65% typical. Motor: IE3 ~94%, IE4 ~96%. Use manufacturer curves for final selection.

Q: How does blowdown affect pump sizing?

Blowdown adds 1-10% to required flow. A 2% blowdown means pump delivers 102% of steam flow.

Units:

Step 1: Flow Rate

Determine required pump flow from boiler capacity.

Input Type

Boiler Horsepower (BHP)

Typical: 10-500 BHP (commercial), 1,500-30,000+ BHP (industrial)

Control Mode

Blowdown (%)

Typical: 1 - %

Safety Margin (%)

Industry standard: 15-25%

Results Summary

Flow Rate

13.2 GPM

3 m3/h

TDH

465.4 ft

141.8 m

Motor

1.8 kW

2.4 HP

Pump Configuration Comparison

1W + 1S2 pumps

1 working + 1 standby, each at 100% capacity

Per Pump

13.2 GPM

3 m3/h

Per Motor

1.8 kW

2.4 HP

Total Installed

3.6 kW

4.8 HP

2W + 1S3 pumps

2 working + 1 standby, each at 50% capacity

Per Pump

6.6 GPM

1.5 m3/h

Per Motor

0.9 kW

1.2 HP

Total Installed

2.7 kW

3.6 HP

3 x 50%3 pumps

3 pumps x 50% capacity, all operating

Per Pump

6.6 GPM

1.5 m3/h

Per Motor

0.9 kW

1.2 HP

Total Installed

2.7 kW

3.6 HP

Boiler Feed Pump Formulas

Flow Rate

GPM = BHP x 34.5
       / (60 x 8.33)
       x CF x (1+BD/100)
       x (1+SM/100)

CF = Circulation Factor (1.5 int. / 1.15 cont.)
BD = Blowdown %, SM = Safety Margin %

Total Dynamic Head

TDH = P x 2.31
      + Hs + Hd
      + Hf + He
      x (1+SM/100)

P = Boiler PSI, Hs = Static suction lift
Hd = Drum height, Hf = Friction loss
He = Economizer drop

Motor Power

WHP = GPM x TDH x SG / 3960

BHP = WHP / eta_p

Motor = BHP / eta_m

eta_p = Pump efficiency (60-75%)
eta_m = Motor efficiency (92-97%)

Worked Example - 90 TPH / 88 Kg/Cm2 Industrial Boiler

Step 1: Flow

TPH = 90 → m3/h = 90 x 1.5 x 1.02 x 1.25 = 172 m3/h
GPM = 172 x 4.403 = 757 GPM

Step 2: TDH

88 kg/cm2 → 880 m head
+ 15 m static + 10 m friction + 3 m economizer
= 908 m x 1.10 = 999 m (3,277 ft)

Step 3: Motor

kW = (172 x 999 x .95 x 9.81) / (3600 x .65 x .95) = ~720 kW (965 HP)

Reference Data

Safety Factor Reference

Standard	Service	Factor
ASME / HI	Continuous	1.15
ASME / HI	Intermittent	1.50
NFPA 85	Boiler feed	1.25
IEC / ISO	Safety margin	10-15%

Water Density vs Temperature

Temp (deg C)	Temp (deg F)	SG	lbs/gal
20 deg C	68 deg F	0.998	8.33
50 deg C	122 deg F	0.988	8.24
80 deg C	176 deg F	0.972	8.10
100 deg C	212 deg F	0.958	7.99
110 deg C	230 deg F	0.950	7.92
150 deg C	302 deg F	0.917	7.65
200 deg C	392 deg F	0.865	7.21

Key Concepts

What Is TDH (Total Dynamic Head)?

TDH is the total pressure the pump must overcome, combining: boiler operating pressure (converted to head), elevation difference between pump and boiler steam drum, pipe friction losses, and economizer/valve pressure drops. It is measured in feet of head (imperial) or meters (metric).

BHP vs TPH vs EDR

BHP (Boiler Horsepower) = 34.5 lbs steam/hr - common in North American commercial HVAC.
TPH (Tonnes Per Hour) = metric steam capacity - used worldwide for industrial boilers.
EDR (Equivalent Direct Radiation) = steam radiator output - legacy method for low-pressure heating.
1 BHP ~139.5 EDR ~34.5 lbs/hr ~15.6 kg/hr.

1W1S vs 2W1S - How Many Pumps?

1W1S: One pump operating, one standby - each sized at 100% flow. Simplest, highest redundancy. Used for critical single-boiler plants.
2W1S: Two pumps operating (each at 50%), one standby - better efficiency at partial loads. Common for multi-boiler installations.
3 x 50%: Three pumps each at 50% capacity - highest flexibility for variable loads. Recommended for plants >200 TPH.

Why Water Temperature Matters

Hot water has lower density than cold water. At 110 deg C, SG ~0.95 vs 1.0 at 20 deg C. This means the pump needs to move more volume for the same mass. The difference is about 5% between cold makeup and deaerated feedwater - significant enough to account for in motor sizing.

Frequently Asked Questions

How do I size a boiler feed pump?

Three steps: calculate required flow from boiler capacity, calculate total dynamic head (TDH) from system pressure and friction losses, then size motor power from flow x head x specific gravity / pump and motor efficiency.

How to calculate feed pump flow rate from BHP?

GPM = BHP x 34.5 / (60 x 8.33) x circulation_factor x (1 + blowdown%) x (1 + safety%). For intermittent operation use x1.5, for continuous use x1.15. Typical blowdown is 2%, safety margin 25%.

How many feedwater pumps are required?

Industry standard is N+1 redundancy. For critical applications: 1W1S (2 pumps). For higher availability: 2W1S (3 pumps x 50%). For large plants >200 TPH: 3 x 50%. Follow NFPA 85 and ASME guidelines.

What is the standard TDH safety margin?

10-15% is standard. ASME recommends 10% for well-defined systems, 15% for uncertain friction losses. Never apply less than 10% for boiler feed service.

What is total dynamic head and how is it calculated?

TDH = boiler operating pressure (converted to feet or meters) + static lift + drum height + friction losses + economizer pressure drop + safety margin. All components are summed to get the total head the pump must overcome.

What is the difference between 1W1S and 2W1S configurations?

1W1S: 1 working + 1 standby pump, each at 100% capacity (2 total). 2W1S: 2 working + 1 standby, each at 50% (3 total). 2W1S offers better part-load efficiency and N+2 redundancy for critical systems.

How does blowdown affect pump sizing?

Blowdown purges concentrated solids from the boiler drum. A 2% blowdown means pump delivers 102% of steam flow. For high TDS feedwater this can reach 5 - 0%, proportionally increasing pump flow requirements.

What pump efficiency should I use for sizing?

Centrifugal pump: 65% typical (range 60-75%). For final selection use manufacturer curve at operating point. Motor: IE3 ~94%, IE4 ~96%. Our calculator defaults to 65% pump and 95% motor.

How do circulation factors and blowdown interact?

Intermittent circulation x1.5, continuous x1.15. These multiply with (1 + blowdown%) x (1 + safety%) to determine total flow factor. Example: intermittent + 2% blowdown + 25% safety = total factor BHP x 0.108 for GPM.