HVAC Pump & Circulator Sizing Calculator

Grundfos HVAC Pumps · Free Sizing Tool

HVAC Pump & Circulator Sizing Calculator

Work out the flow and head for a heating loop, a chilled water plant, data center facility water, a cooling tower or a hot water recirculation line, then see which Grundfos circulators, in-line and end-suction pumps cover it, checked against their published curves.

6Applications
760+Grundfos curves checked
N+1Redundancy built in
1 pagePrintable worksheet

The short version

  1. Flow comes from the load. GPM = BTU/h ÷ (500 × temperature difference). A ton of cooling is 12,000 BTU/h; a kilowatt of IT load is 3,412 BTU/h.
  2. Head comes from the longest circuit. Pipe friction, fittings and the pressure drop through the chiller, boiler, coil or CDU and control valve. In a closed loop the building height does not count.
  3. Glycol needs more flow. It carries less heat per gallon and it is thicker, so the flow and the friction both go up.
  4. Data centers size the standby too. Choose 1+1, 2+1 or 3+1 and each duty pump is sized for its share of the flow.
  5. The match is checked on the curve. Every model shown carries your flow at your head on its published Grundfos 60 Hz curve.
Booster Pump CalculatorDomestic water pressure boosting for buildings.Pressure Tank CalculatorDrawdown and tank size for booster and well systems.Pump Curve 101How to read a curve, the system curve and the duty point.

Size the Pump

Pick what the pump is for, enter the load, and the calculator fills in typical temperatures and pressure drops for that application. Replace any of them with the figures from your drawings or submittals.

1. What is the pump for?

The application sets the formula and the starting values below.

2. Load and temperatures

Design load and the supply-to-return temperature difference.

IT load and the share of its heat that goes into the water. ASHRAE liquid-cooling classes set the maximum facility supply: W17 is 62.6 °F, W27 80.6 °F, W32 89.6 °F.

Length of hot water supply pipe the loop keeps hot, by size, and the number of balancing valves.

Flow and total head from the engineer's schedule.

BTU/h (MBH × 1,000)
Tons of refrigeration
BTU/h per ton: 15,000 for a typical electric chiller
kW
%: 100 for chilled water to CRAHs; 70 to 90 for direct-to-chip
ft, at 10 BTU/h per ft
ft, at 20 BTU/h per ft
ft, at 5 BTU/h per ft per inch of size
in
0.5 GPM each, minimum
GPM, total
ft (PSI × 2.31)
°F leaving the boiler, chiller, tower or heater
°F, supply to return

3. Fluid

Glycol raises both the flow and the friction.

4. Piping

The longest circuit from the pump and back: supply plus return.

ft, supply plus return
% of pipe friction: 50 is typical

5. Equipment pressure drops

Typical values are filled in for the application. Use the submittal figures where you have them.

ft
ft
ft
ft
ft, basin level to spray inlet, plus nozzle pressure

6. Pumps

How many pumps share the duty, and the power you have.

One page on our letterhead: your inputs, the flow and head, and the models that cover it with the curve.

Your Results

Design flow—GPM
Pump head—ft
Best match, % of max flow—60 to 80 % is the sweet spot

Detailed Analysis

Head build-up Feet Basis
Grundfos model Type Head at your flow % of max flow Note

Each model's head at your flow is read between the points of its published Grundfos 60 Hz curve, at full speed. One best model per pump family, ranked by where the duty sits on the curve.

Send this sizing to us

We check it in the Grundfos sizing tool and come back with a selection, a submittal and a price. Your result is attached below.

Thank you, it is on its wayWe have your sizing and will reply by email, usually the same business day. For anything urgent call 1-888.510.4036.

How the Calculator Works

The same two numbers size every HVAC pump: the flow the load needs and the head the piping takes to move it.

Flow from the load

GPM = BTU/h ÷ (500 × ΔT). The 500 is 8.33 lb per gallon × 60 minutes × 1 BTU per lb per °F of water. Chilled water at a 10 °F rise carries 2.4 GPM per ton; condenser water at 15,000 BTU/h per ton and a 10 °F rise needs 3 GPM per ton.

Head from the longest circuit

Pipe friction by Darcy-Weisbach for the actual pipe, fluid and temperature, plus a fittings allowance and the pressure drop through each piece of equipment. A closed loop is full and balanced, so the height of the building does not add to the pump head; an open cooling tower loop adds its static lift.

Glycol

Glycol solutions carry less heat per gallon than water, so the 500 is multiplied by a correction factor: about 0.91 for 40 % propylene glycol at chilled water temperatures. They are also thicker, which raises friction most in cold loops. The calculator applies both.

The match on the curve

Each Grundfos curve is checked at your flow per pump. Fixed-speed pumps should meet the duty without much excess head; variable-speed pumps run anywhere under their top curve and are ranked by where the duty sits, aiming for 60 to 80 % of maximum flow.

Worked exampleA 200-ton comfort cooling plant at 44 °F supply and a 10 °F rise needs 200 × 12,000 ÷ (500 × 10) = 480 GPM. With 500 ft of 5 in steel in the longest circuit, a 50 % fittings allowance, 15 ft through the chiller, 10 ft through the coil, 10 ft through the valve and 5 ft for the strainer, the pump head is about 69 ft: 20 ft of pipe friction, 10 ft of fittings and 40 ft through the equipment.

Pumps for Data Centers

Cooling is the load that never stops. The pump selection follows from three decisions the facility makes first.

Facility water or technology loop

The facility water system carries heat from the CDUs or CRAHs to the chillers, dry coolers or towers; this calculator sizes those pumps. The technology cooling loop inside each CDU runs to the cold plates and is supplied with the CDU.

Warm water

Liquid cooling runs warmer than comfort cooling. ASHRAE's classes cap the facility supply at 62.6 °F (W17), 80.6 °F (W27) or 89.6 °F (W32), which opens up economizer hours, and a wider temperature difference cuts the flow and the pump size.

Redundancy

Concurrently maintainable plants carry at least one standby pump: 1+1 with each pump at full flow, or 2+1 and 3+1 with each duty pump at its share. Twin-head MAGNA3 D and TPE3 D pumps put a duty and a standby in one body for smaller loops.

Variable speed on differential pressure

Load follows the IT racks, so the flow does too. Variable-speed pumps held on a differential-pressure signal at the far CDU save energy at part load; the TPE3, MAGNA3 and the NBE, NKE and NBSE end-suction pumps take the sensor signal directly.

Also on the site for these plants: Grundfos DELTA HCU packaged pumping systems, GCBT chilled water buffer tanks, GFXA expansion tanks, glycol make-up packages and differential pressure sensors.

Choosing the Type of Pump

The duty point decides the size; the installation decides the type.

Type Grundfos range on our site Typical duty Best for
Wet-rotor circulator MAGNA3, MAGNA1, UPS, ALPHA Up to about 330 GPM and 58 ft Closed heating and cooling loops, zone and secondary pumping; no seal to maintain
In-line, dry rotor TPE3, TP Up to about 340 GPM single head, 525 GPM twin head Hanging in the pipe where floor space is short; variable speed on the TPE3
Vertical in-line, split coupled VLS Larger flows at 1800 rpm Mechanical rooms that want the seal serviced without breaking the piping
End suction NBE, NB, NKE, NBS, NBSE To several thousand GPM and over 200 ft Central plants, condenser water and data center facility water

For potable hot water recirculation only bronze and stainless steel builds are used: Comfort, ALPHA HWR, UP and UPS bronze or stainless, MAGNA3 N and MAGNA1 N, TP bronze and TPE3 stainless.

Questions

Why does the building height not count?

In a closed loop the water going up the supply riser is balanced by the water coming down the return. The pump only overcomes friction. The expansion tank's fill pressure handles the height. An open cooling tower loop is different: the pump lifts water from the basin to the spray nozzles.

What temperature difference should I use?

Typical design values are 20 °F for hot water heating, 10 to 12 °F for comfort chilled water, 10 °F for condenser water and 15 to 20 °F for data center facility water. A wider difference means less flow and a smaller pump, if the coils are selected for it.

How is a recirculation pump sized?

From the heat the hot water supply piping loses: about 10 BTU/h per foot for insulated pipe under 2 in and 20 for 2 to 4 in, a 10 °F drop to the last fixture, and at least 0.5 GPM per balancing valve. That is the method R. L. Deppmann publishes for domestic hot water recirculation.

Is the result a final selection?

No. It is a starting point from estimating figures and the published curves. Send it to us and we confirm the selection in the Grundfos sizing tool, with efficiency, NPSH and motor size, before anything ships.

Send Us the Duty

Flow, head, fluid and how many pumps. We size it in the Grundfos tool and send a selection, a submittal and a price.

1-888.510.4036sales@watermainsupply.com
Genuine Grundfos equipment, factory-new in original packaging — sold and supported by Watermain Supply, an independent industrial supplier.

Other calculators: Booster Pump · Pressure Tank · Well & Irrigation Pump · Solar Water Pump · Submersible Well Pump · Sump, Sewage & Dewatering Pump · Pump Curve 101

Flow, head and fluid figures on this page are estimating figures for planning. Pump data is taken from Grundfos product literature (published 60 Hz curves) and is subject to change by the manufacturer. Confirm against the current installation manual before specifying. Grundfos, MAGNA3, MAGNA1, ALPHA, TPE3 and DELTA HCU are trademarks of Grundfos Holding A/S, used here for product identification only. Watermain Supply is a DBA of E4 Industrial LLC, an independent industrial supplier based in Houston, Texas.
© Watermain Supply — A division of E4 Industrial LLC