Heating Degree Day Cost Estimator
Heating degree days provide a weather-normalized measure of how much colder a period was relative to a chosen base temperature. This model estimates energy from a heat-loss coefficient and a seasonal efficiency assumption.
How to use this calculator
- Use HDD values calculated with a base temperature appropriate to the building and compare equivalent periods.
- Check that the input values use the same units and reporting period before comparing scenarios.
- Change one assumption at a time to see which input drives the result.
Formula and method
Useful heat (kWh) ≈ heat-loss coefficient (W/K) × heating degree days × 24 / 1,000; purchased energy = useful heat / efficiency.
- Useful heat ≈ 9,504 kWh; purchased energy ≈ 10,560 kWh.
- Degree-day base temperature, internal gains, solar gains, thermostat behavior, seasonal system performance and weather vary. This is a simplified scenario model.
Worked examples
Worked example
A 180 W/K heat-loss coefficient and 2,200 heating degree days, at 90% seasonal efficiency.
Useful heat ≈ 9,504 kWh; purchased energy ≈ 10,560 kWh.
The estimate yields about 10,560 kWh of purchased energy before tariff-specific charges.
Understanding the result
The estimate yields about 10,560 kWh of purchased energy before tariff-specific charges.
Degree-day base temperature, internal gains, solar gains, thermostat behavior, seasonal system performance and weather vary. This is a simplified scenario model.
Important notes
Use HDD values calculated with a base temperature appropriate to the building and compare equivalent periods.
The displayed result uses the entered assumptions; validate important estimates against source measurements, specifications or qualified guidance.
Frequently asked questions
Does this size a boiler or heat pump?
No. It estimates seasonal demand and is not a peak heating-load design calculation.
Does efficiency above 100% make sense?
For some heat pumps, coefficient of performance can exceed one; this field is explicitly a simple efficiency fraction and is capped at 100%.
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Learn the method behind the number or compare the terminology before using the calculator.
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This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.