How It Works
Overview
EnerCalc estimates the heating capacity your home needs by analyzing the relationship between outdoor temperature and your gas consumption. This technique is known as a degree-day regression and is used by energy auditors and HVAC engineers to right-size heating equipment.
Key Assumptions
- Gas consumption is primarily for space heating (not pool heaters, etc.).
- Your home's heating characteristics haven't changed significantly during the billing period (no major insulation upgrades, etc.).
- Natural gas heating value: 37,963 BTU/m³ (CSA Z21.47 Table 10).
- Indoor design temperature: 22°C (NBCC 9.33.5.2 minimum).
- Design temperature: January 2.5 percentile from NBCC 2015 Table C-2.
Data Sources
- Weather data: Meteorological Service of Canada daily climate observations.
- Geolocation: Natural Resources Canada geolocation service.
- Design temperatures: National Building Code of Canada 2015 Table C-2.
Interpreting Results
The calculated equipment size is the minimum size required based on your actual energy consumption. This estimate takes into account all sorts of things that are otherwise hard to measure: air leakage, insulation levels, heat from appliances, exposure to sun and wind, and even the body heat of the occupants.
The output from the calculator is intended to be a starting point for a discussion with an HVAC professional. There may be factors that need to be considered that are not included in the calculations. However, there is also a tendency in the industry to oversize residential heating systems. It's not uncommon to be offered systems that are more than twice as big as they need to be. If that's the case for you, ask questions and make sure there is a good justification for the system size you are offered.