When condensate has to get back to the boiler room, three numbers do most of the work in sizing the pump: how high it must lift, how much back pressure it works against, and how much friction the piping adds. Getting them right is the difference between a pump that runs smoothly and one that struggles. This article explains each, using the inputs on the Skidmore Pump condensate calculator. It is general information and results should be confirmed by a qualified engineer.
Start With the Load
The calculator first asks for the load and the load type. Options include boiler horsepower, equivalent direct radiation, pounds of steam, BTU per hour, and MBH. From the load it returns flow in GPM, results for duplex and single pump arrangements, and an automatically sized receiver in gallons.
Number One: Lift
Lift is the vertical distance the pump must raise condensate, entered in feet. Measure from the receiver outlet to the highest point in the discharge piping. Every extra foot adds to the pressure the pump must produce.
Number Two: Back Pressure
Back pressure, in PSIG, is the pressure the condensate is pushing against at the destination. If it is guessed low, the pump may not deliver at the flow rate you expect.
Number Three: Friction Loss
Friction loss, also in PSIG, reflects the resistance of piping, fittings, and valves. Long runs with many elbows lose more than short straight ones.
Putting the Numbers Together
With these three values the tool calculates the minimum pump discharge pressure in PSIG. The page also offers a manual calculation option for engineers who prefer to check the math themselves.
A Quick Input Sheet
- Connected load and load type
- Lift in feet
- Back pressure in PSIG
- Friction loss in PSIG
- Preferred pump arrangement
Common Input Mistakes
People mix units, measure lift to the wrong point, or ignore friction in long runs. A short review with a colleague catches most of these before the numbers reach a quote.
Where to Read More
Engineers and facility staff looking for a condensate return calculator can use the tool on the Skidmore Pump website, which is part of a set that also includes boiler feed, vacuum condensate, vacuum assisted boiler feed, and NPSHa calculators.
What to Do Next
Skidmore advises contacting your area representative for a quote once sizing is complete, and mentions the Skidmore Configurator for self-quotations. Treat the calculator output as a starting point and have a qualified engineer confirm the final selection.
