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Free Windows tool for sizing hydronic pipes (chilled/hot & condenser water) by velocity or friction method — from McQuay/Daikin.
The McQuay Pipe Sizer is a free Windows program for hydronic pipe sizing — selecting the correct pipe diameter for chilled-water, hot-water and condenser-water systems. Developed by McQuay International (now Daikin Applied), the McQuay Pipe Sizer software lets HVAC engineers, designers and contractors size water piping in seconds by the velocity method or the friction (pressure-drop) method, instantly returning the pipe size, water velocity and friction loss for a given flow rate. It is the plumbing-and-hydronics companion to the well-known McQuay Duct Sizer, and like that tool it is fast, free, accurate and tiny — which is why it is one of the most widely downloaded pipe sizing calculators in the HVAC world. This page is a complete guide to what the McQuay Pipe Sizer does, the pipe-sizing theory it automates, how to use it, and how to download it.
From a small chilled-water branch to a large condenser-water main, the McQuay Pipe Sizer replaces friction-chart look-ups and hand calculations with instant answers, helping you keep water velocity in the right range for quiet, erosion-free operation while holding friction loss low enough to minimize pump energy. Below you will find the tool's features, step-by-step instructions, the velocity and friction methods behind it, material and velocity guidance, common mistakes, and answers to frequent questions.
The McQuay Pipe Sizer is a standalone pipe sizing software that determines the required pipe diameter for a given water flow rate based on either a target velocity or a target friction rate. You enter the flow (in GPM or L/s), select the sizing basis, and the tool returns the recommended pipe size along with the resulting velocity (ft/s or m/s) and the friction head loss (ft per 100 ft, or Pa/m). It covers the standard pipe sizes used in hydronic systems, works in both IP and SI units, is distributed as freeware with no license key, and runs on any modern version of Windows in a package only a few megabytes in size.
Because it is built on the same Hazen-Williams and Darcy-Weisbach friction relationships used throughout hydronic design, the McQuay Pipe Sizer produces results consistent with the ASHRAE Handbook pipe-friction charts and with standard plumbing-engineering practice. That makes it a trustworthy quick-sizing tool for chilled-water, hot-water, condenser-water and general water piping.
Pipe sizing is the process of choosing a pipe diameter that carries the required water flow while balancing two limits: keeping the velocity low enough to avoid noise, erosion-corrosion and water hammer, and keeping the friction loss low enough to limit pump energy and preserve available pressure. A pipe that is too small runs fast, noisy and lossy and can erode over time; a pipe that is too large wastes material and money and can let water stagnate. The McQuay Pipe Sizer finds the balance instantly.
The governing relationship is the continuity between flow, velocity and area — velocity equals flow divided by cross-sectional area — combined with a friction equation (Hazen-Williams for water, or the more general Darcy-Weisbach) that relates flow and diameter to head loss. For water in a pipe, a convenient form gives velocity as 0.408 times the flow in GPM divided by the square of the inside diameter in inches. The McQuay Pipe Sizer encodes this math so you never have to read a friction chart by hand.
The velocity method caps the water velocity to control noise, erosion and water hammer. Typical limits are about 4 ft/s in occupied areas for quiet hydronic operation, up to 6–8 ft/s in mechanical rooms and large mains, with hot-water and recirculation lines held even lower (2–3 ft/s) to prevent erosion-corrosion of copper. The McQuay Pipe Sizer sizes the pipe to your chosen velocity limit, which is the governing criterion for branches and occupied-space piping.
The friction method sizes each pipe section to a target friction rate — often around 4 feet of head per 100 feet of pipe — so the whole system shares a consistent pressure gradient. This controls pump energy and helps balance the system, and it typically governs the larger mains where velocity is comfortably within limits. The tool lets you size to a friction rate directly, reading the pipe size, velocity and loss at once.
In practice, occupied-space branches end up velocity-governed and mains end up friction-governed, so good hydronic design uses both checks together — exactly what the McQuay Pipe Sizer lets you do by switching the sizing basis.
The material affects both the sizing and the behavior of the system. Copper is a hydronic standard but is vulnerable to erosion-corrosion above about 5 ft/s in hot water, so hot and recirculating lines are kept slow. Steel is used for large mains and higher-temperature service. PEX and CPVC are common in modern hydronic and plumbing systems, with slightly different inside diameters for the same nominal size, so velocity should be checked on the true bore. Whatever the material, keeping the velocity in the recommended band does more than control friction — it protects the pipe from erosion and the system from water-hammer damage, extending service life. The McQuay Pipe Sizer reports the velocity for the chosen size so you can keep it safely within the material's limit.
The McQuay Pipe Sizer software saves time by replacing friction-chart look-ups with instant results, letting you size a whole hydronic system in minutes. It reduces errors by removing manual interpolation. It standardizes designs to accepted friction data, so results are consistent across a team and defensible in review. It is free, so every engineer, estimator and student on a project can use it. And it is fast to learn — anyone who has sized pipe by hand is productive immediately. For contractors and estimators, the speed means faster take-offs and more competitive bids; for students, it is an excellent way to learn how flow, velocity, friction and pipe size relate; for engineers, it is the quick check that validates a piping layout before it goes into CAD or a pump schedule.
The McQuay Pipe Sizer is a desktop program — convenient offline but tied to a Windows machine. A modern alternative is an online pipe sizing calculator that runs in any browser on any device, always up to date and requiring no download. MEPMate's free Pipe Sizing Calculator performs the same velocity and friction sizing in the browser with US-first units, and it is joined by dedicated tools for chilled-water pipe sizing, pump head (TDH) and hot-water pipe sizing. Because the underlying Hazen-Williams and Darcy-Weisbach math is the same, the desktop and online results agree, so many engineers keep the McQuay Pipe Sizer for offline work and use an online calculator for quick checks and for pairing with pump-head and flow tools.
Get the most from the McQuay Pipe Sizer by designing mains to a consistent friction rate and letting branches be velocity-governed, keeping hot and recirculating lines slow (2–3 ft/s) to prevent erosion, and confirming the velocity on the true inside diameter of the actual material. Reserve pressure for the worst-case load, add water-hammer arrestors at quick-closing valves, and always add fitting equivalent lengths and equipment pressure drops to the pipe friction when sizing the pump. A higher chilled-water ΔT reduces the flow and therefore the pipe size and pump energy — a low-cost efficiency win if the coils are selected for it.
Alternatives to the McQuay Pipe Sizer include full hydronic design suites that size piping as part of a complete system model, manufacturer utilities from other equipment makers, and browser-based pipe calculators such as the free MEPMate Pipe Sizing and Pump Head tools. For a quick, accurate pipe size the McQuay Pipe Sizer and a good online calculator are interchangeable; for full system design with fittings, equipment drops and pump selection, a complete hydronic tool or a spreadsheet built on the same friction data carries the design further.
Yes. The McQuay Pipe Sizer is freeware from McQuay/Daikin, with no cost, license key or activation. It is a small Windows program, which is why it is so widely used by HVAC and plumbing engineers for quick hydronic pipe sizing.
It sizes pipe by the velocity method (capping water velocity) and the friction method (sizing to a target friction rate), using standard Hazen-Williams and Darcy-Weisbach friction relationships — the same basis as the ASHRAE Handbook pipe-friction charts.
Yes. It is suited to all common hydronic loops — chilled water, hot water and condenser water — as well as general water piping, because the velocity and friction physics is the same for all water systems; you simply enter the flow and choose the sizing basis.
Design for about 2–4 ft/s in occupied areas for quiet operation, up to 6–8 ft/s in mechanical rooms and large mains, and keep hot-water and recirculation lines at 2–3 ft/s to prevent erosion-corrosion of copper. The McQuay Pipe Sizer reports the velocity for each size so you can stay within these limits.
It is a Windows program and runs on modern versions of Windows in a small, low-resource package that works offline, making it convenient for field use.
It is accurate for sizing individual pipe sections because it uses standard water-friction relationships. A complete hydronic design also requires adding fitting and equipment pressure drops and confirming the pump can deliver the total head — the tool sizes the pipe, and the surrounding design completes the system.
Yes. A browser-based tool such as the free MEPMate Pipe Sizing Calculator does the same velocity and friction sizing on any device with no download, and because it uses the same math the results match. It also pairs naturally with online pump-head and chilled-water tools for a complete workflow.
Both balance velocity against friction, but pipe sizing handles incompressible water with erosion and water-hammer concerns, while duct sizing handles air with noise and space concerns. The McQuay Pipe Sizer and McQuay Duct Sizer are companion tools that apply the same design philosophy to water and air respectively.
The McQuay Pipe Sizer balances two quantities, and understanding them makes you a better designer. Velocity — the speed of the water, in feet per second — controls noise, erosion and water hammer. Too slow and the pipe is oversized and may not scour sediment; too fast (above about 7–8 ft/s) and you get noise, erosion-corrosion of copper, and larger water-hammer surges when valves close. Friction loss — the head lost to friction, in feet of head per 100 feet of pipe — determines pump energy and how much of the available pressure remains for the loads. Because friction loss rises with roughly the square of velocity, a modestly larger pipe can sharply cut pump energy: doubling the pipe area (going up about one nominal size) can reduce the friction loss by a factor of several. This is why continuously operating systems justify slightly larger pipe than the minimum — the pumping-energy savings over the system's life outweigh the extra material. The McQuay Pipe Sizer shows both velocity and friction so you can find the balance for each section.
The pump energy connection is direct: the pump must overcome the total dynamic head, which is the sum of static lift, the friction of every pipe section and fitting, the equipment pressure drops (chiller, coils, control valves), and the required residual pressure. Pipe friction is a controllable part of that total, and sizing it well — using the McQuay Pipe Sizer to keep friction in a reasonable band — keeps the pump smaller and the operating cost lower. In variable-flow systems the payoff is amplified, because pump power falls with the cube of flow when a variable-speed drive slows the pump at part load.
The McQuay Pipe Sizer handles all the common HVAC water loops, each with its own considerations. Chilled-water pipe carries the cooling flow from the chiller to the coils — about 2.4 GPM per ton at a 10°F temperature difference, less at a higher ΔT — and is typically sized to a moderate velocity for quiet operation, since it runs during the whole cooling season. Hot-water heating pipe is sized similarly but with attention to the lower velocity limit that protects copper from erosion at elevated temperature, and hot-water recirculation lines are kept especially slow because they run continuously. Condenser-water pipe carries the larger flow between the chiller and the cooling tower — about 3 GPM per ton — and is often sized to a friction target because velocity is comfortably within limits at that flow. For each loop, you enter the flow and let the McQuay Pipe Sizer return the size, velocity and friction, then apply the appropriate velocity limit for the fluid and temperature.
Pipe sizing is one step in designing a complete hydronic system, and the McQuay Pipe Sizer fits into a clear sequence. First is the load and flow calculation — the cooling or heating load sets the required water flow (GPM) at the design temperature difference. Next is pipe sizing, where the McQuay Pipe Sizer turns each section's flow into a pipe size at the chosen velocity or friction basis. Then comes the head tally — adding the friction of every pipe section, the fitting equivalent lengths, and the equipment pressure drops along the critical path to find the total dynamic head. That head, with the flow, drives pump selection, ideally near the pump's best-efficiency point. Finally the system is balanced so each coil and terminal receives its design flow. By producing accurate pipe sizes instantly, the McQuay Pipe Sizer keeps this workflow efficient and lets the engineer focus on the head tally, pump selection and balancing that determine how well the system performs.
Reliable hydronic designs follow a few habits. Check velocity and friction together, letting branches be velocity-governed and mains friction-governed. Keep hot and recirculating lines slow to prevent erosion. Always add fittings and equipment to the head tally — the pipe friction alone will badly under-predict the pump head. Use the true inside diameter for the material when checking velocity. If a system underperforms, common causes are an undersized pump because fitting and equipment losses were omitted, low delta-T forcing more flow than designed, air binding, or a fouled strainer raising resistance. The McQuay Pipe Sizer prevents the pipe-sizing errors; a complete head tally and proper commissioning prevent the rest. Adding a higher chilled-water ΔT at the design stage shrinks the flow, the pipe and the pump together — one of the cheapest efficiency improvements available.
The pipe material you select alongside the McQuay Pipe Sizer affects both the sizing and the long-term performance of the system. Copper is a long-standing hydronic standard — durable, smooth (a Hazen-Williams C around 150) and available in types L and M — but it is vulnerable to erosion-corrosion above about 5 ft/s in hot water, which is why hot and recirculating copper lines are held slow. Steel (black or galvanized) is used for large mains and higher-temperature service; galvanized water pipe corrodes and tuberculates with age, dropping its effective C toward 100 and shrinking its bore, a common cause of low flow in old buildings. PEX has become popular in modern hydronic and radiant systems for its flexibility, freeze tolerance and quiet operation, though its inside diameter is smaller than copper of the same nominal size, so velocity should be checked on the true bore. CPVC handles hot water at lower cost but is more brittle. Whatever the material, matching the roughness coefficient and the actual inside diameter to it — and respecting its velocity limit — is what makes the McQuay Pipe Sizer's results translate into a durable, quiet, efficient piping system.
When sizing with the McQuay Pipe Sizer, keep water velocity within these limits: about 4 ft/s in occupied areas for quiet operation, up to 6–8 ft/s in mechanical rooms and large mains, and 2–3 ft/s for hot-water and continuously running recirculation lines to prevent erosion-corrosion of copper. As a capacity guide at roughly 4 ft/s, common pipe sizes carry approximately: ¾-inch ≈ 5 GPM, 1-inch ≈ 10 GPM, 1¼-inch ≈ 16 GPM, 1½-inch ≈ 23 GPM, 2-inch ≈ 42 GPM, 3-inch ≈ 92 GPM, and 4-inch ≈ 160 GPM. For flow, chilled-water systems need about 2.4 GPM per ton at a 10°F ΔT and condenser water about 3 GPM per ton. These anchors, with the McQuay Pipe Sizer's instant calculations, let you size a complete hydronic system quickly while keeping every line quiet, erosion-free and energy-efficient. For the same sizing and reference on any device, the free MEPMate Pipe Sizing Calculator and Pump Head Calculator provide identical friction-based results in the browser.
The McQuay Pipe Sizer is a fast, free and accurate way to size hydronic and water piping by the velocity and friction methods — the pipe-sizing companion to the McQuay Duct Sizer. Use the download button on this page to get the software, and pair it with MEPMate's free online Pipe Sizing Calculator, Pump Head Calculator and Chilled Water Pipe Sizing Calculator for a complete, browser-based hydronic-design workflow. Whether you prefer the offline convenience of the desktop tool or the anywhere access of an online calculator, the friction-based results are consistent, so you can size piping quickly and confidently for any project.
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