Expansion Tank Sizing Calculator
Preliminary diaphragm tank planning for closed-loop hydronic systems with absolute-pressure, glycol, and source-warning checks
Free expansion tank sizing calculator for HVAC technicians and hydronic system designers. Enter system volume, fill and operating temperatures, fill pressure, relief valve setting, fluid, and pipe material to screen required tank volume and a local standard tank size. The app converts gauge pressure to absolute pressure and includes a quick system-volume estimator, but the local water, glycol, pipe, and tank rows remain source-gap planning data that must be verified against current ASHRAE access, manufacturer submittals, code/AHJ rules, and field commissioning data.
Calculate glycol freeze protection concentration
Glycol Freeze Protection Calculator →Check hydronic pipe flow and friction assumptions
Hydronic Pipe Sizing Calculator →Check water hammer risk in piping systems
Water Hammer Calculator →Check heat exchanger duty and LMTD
Heat Exchanger Duty Calculator →How It Works
-
Enter System Volume
Enter the total system water volume in gallons. Use the built-in quick estimator to add up pipe footage by nominal size, boiler volume, and radiator/baseboard volumes if you don't know the total.
-
Set Temperatures and Pressures
Enter fill temperature, maximum operating temperature, cold fill pressure, relief valve setting, and the operating margin. The calculator converts to absolute pressure for the pressure ratio.
-
Select Fluid and Pipe Material
Choose water or glycol and pipe material. Treat local glycol and pipe rows as planning assumptions until checked against current product data and project piping.
-
Read the Tank Recommendation
Review the required volume and local standard size, then verify the tank model, acceptance volume, pre-charge, relief valve, code/AHJ requirements, and commissioning procedure.
Built For
- HVAC contractors screening expansion tank assumptions before manufacturer verification
- Mechanical engineers checking preliminary hydronic heating and chilled-water tank inputs
- Service technicians documenting troubleshooting assumptions before replacing a tank
- Hydronic system designers comparing water and glycol planning cases with source-gap warnings
- Plumbing contractors coordinating closed-loop tank selection with code/AHJ and product data
Assumptions
- System is a closed loop with a diaphragm-type expansion tank.
- Specific volume data is a local planning table and is not a licensed current ASHRAE table reproduction.
- Glycol expansion factors are local multipliers that require current product data and field concentration verification.
- Piping expansion coefficients are averaged planning values and require actual material, dimensions, and manufacturer/project validation.
References
- ASHRAE 2024 HVAC Systems and Equipment Handbook source pointer for hydronic context
- ASHRAE Handbook Online Hydronic Heating and Cooling chapter source pointer for expansion tank context
- ASHRAE 2025 Fundamentals source pointer for property-table context
- Dow DOWFROST and DOWTHERM SR-1 product source pointers for glycol heat-transfer fluid context
- ASME BPVC Section VIII and adopted mechanical code source pointers for pressure-vessel/code review context
Frequently Asked Questions
Learn More
Expansion Tank Sizing for Hydronic Systems: Planning Method
How to size diaphragm expansion tanks using the ASHRAE formula. Gauge vs absolute pressure, glycol correction factors, system volume estimation, and common sizing errors.
Glycol Freeze Protection: Concentration, Performance, and Source Gaps
Selecting the right glycol concentration for freeze protection without over-concentrating. Freeze vs burst point, viscosity penalties, heat transfer derating, and annual maintenance.
Related Tools
Mini-Split Efficiency & Cost Calculator
Is your mini-split cheaper than propane right now? Enter your electric rate and fuel prices to find the exact outdoor temperature where your heat pump stops saving money and your backup heat wins.
Heat Load from Bills Calculator
What size furnace or heat pump do you actually need? Skip the $300 Manual J - estimate your home's BTU/hr heat load from your gas, propane, or electric bills. See how your home compares by age and climate zone.
Heating Bill ROI Calculator
Will a heat pump pay for itself? Enter 12 months of heating bills to see payback period, annual savings, and NPV analysis. Uses HDD regression and real COP curves for accurate projections.