The Ecosizer is a free tool for sizing central water heating systems based on commercial heat pump water heaters (CHPWHs) in multifamily and commercial buildings. The tool is designed to support the building industry to adopt CHPWHs to improve energy efficiency and reduce greenhouse gas emissions. The Ecosizer is also intended to provide educational information on CHPWH system designs to other stakeholders, for example energy efficiency and building decarbonization advocates, program administrators and implementors, building science researchers, manufacturers, and policy makers.

More Information
how to use this tool
  1. Identify weather conditions (cold water temperature and ambient temperature) on the design day, which is usually the coldest day of the year.
  2. Select a HPWH technology and identify its temperature setpoint limitations. Consider its potential performance limitations under winter design conditions.
  3. Provide input method and values to determine design-day hot water demand.
  4. Provide the storage, delivery, and incoming water temperature settings for your system.
  5. Select the configuration for the temperature maintenance system.
  6. Revise default values for advanced inputs, if needed.
  7. Click “Size Your System” to obtain minimum sizing results and the Primary Sizing Curve.
  8. Select the actual HPWH heating capacity according to performance characteristics of the selected HPWH technology. Use the Primary Sizing Curve to find the minimum storage volume based on the actual HPWH design-day heating capacity. Alternatively, select a storage volume first and use the Primary Sizing Curve to find the corresponding HPWH output capacity needed to meet the design-day hot water demand.
Custom Load Shape

Click here to do custom load shape simulation

Disable California Mode to edit

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Peak Gallons per Day per Person calculated based on the expected 98th percentile of the specific combination of apartments sizes

Water Temperature

Locked to CBECC-Res

Temperature Maintenance System

Parallel Loop Tank

Not available in California
Specification Mode

A temperature maintenance system provides hot water to the taps in a timely manner.

Recirculation Loop

Watts / Apt

Calculated by Flow Rate & Return Temperature



Load Shift

Load Shift only available when multifamily building is selected.
Period 1 6–10
Period 2 16–21

Ecotope, Southern California Edison (“SCE”), Sacramento Municipal Utility District (“SMUD”), Bonneville Power Administration ("BPA"), Northwest Energy Efficiency Alliance ("NEEA"), and Oakridge National Laboratory ("ORNL") provide this software program (“Ecosizer”) for the intended “educational and informational” purposes only, and none of these funders guarantees that the information provided by the software is correct, complete, or current. While the computational results of the software may be used only for your design considerations, they should not be used for determining compliance with any applicable federal, state, or local laws or regulations. Please consult a professional to ensure accuracy for your particular requirements.

It is a condition of us allowing you free access to this Ecosizer software program that you agree to the following:

  • None of these funders, nor any of their employees, directors, owners, contractors or subcontractors, will be liable for any action you take in reliance on the information provided by the software. Additionally, you understand and agree that none of these funders makes any warranty, express or implied; or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any data, information, method, or results disclosed in this Ecosizer software program; or represents that its use will not infringe any privately-owned rights including, but not limited to patents, trademarks or copyrights.
  • Ecotope, SCE, SMUD, BPA, NEEA, and ORNL are providing this information in good faith for the intended “educational and informational” purposes only.

By using the Ecosizer software program and downloading results, you agree to the above conditions, and if you provide comments and suggestions for improvements to the software program they may be used for any purpose without restriction, obligation or remuneration of any kind.