Calculate supplemental heating needed after entered heat-pump capacity and other available heat.
Trades & Professional Tools · HVAC
Enter your project measurements
Measured inputs · visitor-entered product and design assumptions
1EnterProvide the known values
2CalculateResults update automatically
3VerifyReview the details and units
Try an example
Use one consistent unit basis and measurements taken at the stated locations and operating condition. Enter project, manufacturer, fluid-property, pressure-temperature, efficiency, and test criteria from the actual system. Values stay in this browser.
Trade calculator result
Enter valid values to see the result.
Your entries are calculated in this browser and are not submitted to 365CALCS.COM.
Calculate supplemental heating needed after entered heat-pump capacity and other available heat.
A load calculation keeps the source of heat gain or loss visible: envelope, outdoor air, people, lighting, equipment, or a selected air-side temperature difference.
At a glance
See the HVAC relationship
Heat sources, load, and an equipment comparison. This is a simple reading map for this kind of calculation; it does not represent a complete installed system.
Design heating load (kW)Heat-pump capacity at design condition (kW)Other available heat (kW)
This calculator applies that relationship to your entries. Use the formula to check that the units, reference condition, and measurement location make sense together.
Field reading
Use the result as a next check
1. Describe one real condition
Enter values from the same system state, period, unit basis, and measurement location.
2. Read the relationship
Build one stated condition at a time and compare the output with a documented design load or manufacturer performance point—not a generic rule of thumb.
3. Keep the boundary clear
It does not perform Manual J, D, or S; select equipment; establish design weather; or approve a heating or cooling system.
Quick guide
How to use this calculator
Choose the calculation mode or measurement system that matches the values you actually have.
Enter measured project dimensions and use product-specific coverage, density, yield, resistance, or waste data where requested.
Review the intermediate results before ordering material or applying the result on site.
The calculator preserves full internal precision and rounds only displayed results. Quantity outputs round up when whole purchasable pieces are required.
Worked example
Worked example
15 kW load minus 9 kW heat pump and 1 kW other heat needs 5 kW.
HVAC results use the measured, design, manufacturer, psychrometric, fluid-property, pressure-temperature, efficiency, and test values you enter. They do not perform or certify Manual J, D, or S procedures; supply ventilation or code defaults; select equipment; identify refrigerant; determine a safe charge; authorize combustion, pressure, electrical, or refrigerant work; or replace approved manufacturer data and a qualified HVAC professional.
Planning scope
This calculator supports measurement, estimating, and scenario planning. It does not inspect a site, select a product, certify a design, or replace drawings, specifications, manufacturer instructions, local codes, permits, or a qualified trade professional.
Measured and product-specific inputs
Nominal dimensions can differ from actual dimensions. Verify inside pipe diameters, actual lumber sizes, product coverage, bag yield, material density, conductor resistance, waste, and packaging against the materials used on the project.
Safety and regulatory limits
Electrical, HVAC, structural, excavation, roofing, pressure, lifting, and life-safety work may require jurisdiction-specific calculations and professional approval. Do not use a generic planning result as a code-compliance or safety determination.
Precision and privacy
Inputs accept bounded plain decimals. Calculations remain in this browser and raw entered project values are not submitted to 365CALCS.COM.
