Hydronic pipe planning starts with a heat-transfer question: how many BTU/hr must the circuit deliver, and what flow is required at the chosen temperature difference? That flow screen depends on fluid properties, pipe material, straight-pipe friction, velocity limits, fittings, equipment pressure drops, pump curves, and commissioning requirements.
This guide explains the local planning math used by the ToolGrit screen and points to ASHRAE, ASTM, CDA, Dow, and Bell & Gossett source locations. It is not a licensed ASHRAE table reproduction, product submittal, pump selection, index-circuit head calculation, balancing procedure, code/AHJ approval, or final hydronic design.
Calculating Flow Rate from Heat Load
The familiar water shortcut is:
GPM = BTU/hr ÷ (500 × ΔT)
The 500 factor is the rounded product of local water density, minutes per hour, and specific heat. For a 100,000 BTU/hr load at a 20°F temperature drop, the water shortcut gives about 10 GPM.
Glycol changes the flow screen because density and specific heat change with concentration, product, and temperature. The ToolGrit app uses local density and Cp approximations to adjust GPM, but it does not viscosity-correct friction loss or reproduce current ASHRAE/Dow tables.
Hydronic Pipe Sizing Calculator
Preliminary hydronic pipe planning for copper Type L, Type M, and black steel Schedule 40 using BTU/hr, delta-T, local fluid rows, straight-pipe friction, and velocity warnings.
Friction Loss and Velocity Limits
Friction and velocity are screening limits, not complete design approval. Straight-pipe friction affects pump head and operating cost; velocity affects noise, erosion, air transport, and control stability. The local app compares each listed pipe size against the entered straight-pipe friction and velocity limits.
Final pump head still needs the index circuit, equivalent lengths, fittings, valves, strainers, coils, boilers, heat exchangers, control valves, air and dirt separators, and manufacturer pressure-drop data. Final velocity criteria depend on material, location, noise tolerance, air management, water treatment, and project specifications.
Pipe Materials and Their Characteristics
The current app screens local rows for Copper Type L, Copper Type M, and Black Steel Schedule 40 only. Copper tube uses copper tube sizing, while steel pipe uses iron pipe sizing, so the same nominal size can have a different inside diameter.
Material selection is a project decision. Verify actual dimensions, pressure/temperature rating, joining method, corrosion allowance, water treatment, oxygen diffusion, insulation, supports, concealment, product listing, and adopted code/AHJ requirements. PEX, CPVC, stainless, HDPE, grooved systems, and manufacturer-specific hydronic products are outside the current app rows.
Multi-Zone Pipe Sizing
In a multi-zone screen, the header carries total entered flow while each branch carries its own zone flow. That is useful for comparing branch and header rows, but it is not a full distribution model.
Real systems need the index circuit, equivalent length, zone valves or control valves, manifolds, terminal units, air separators, strainers, checks, balancing valves, and pump curve. Shorter circuits normally require balancing and commissioning to deliver design flow without starving the index circuit or overpumping nearby branches.