Let's break down the load calculation for a single-family dwelling without air conditioning using 220.82 and address the gas central heating system.

Understanding 220.82

220.82 is the Optional Feeder or Service Load Calculation for Dwellings. It's an alternative method to the standard method (220.10 through 220.56) and often results in a lower calculated load. This is useful for dwellings where the service or feeder size is a concern.

Analyzing the Gas Central Heating Load

The crux of your question revolves around where the 120V gas central heating load fits into 220.82. Here's a breakdown:

220.82(C)(6): "Other Heating System" This is your best fit under 220.82. Gas furnaces do require electricity for the controls, draft inducing fans, and other elements. This is an acceptable way to calculate the load. If there is a supplemental electrical heating source in the home, such as a space heater or heated towel rack, 220.82(C)(5) may become applicable. 220.82(B)(3)(a)

This section deals with fixed electric space heating. Since a gas furnace is not electric space heating, this section will not apply.

In Summary

For a gas central heating system with a 120V component, use

220.82(C)(6) "Other Heating System" for the load calculation.

Important Considerations



Nameplate Rating

Use the nameplate rating of the 120V gas furnace for the "other heating system" load in your calculation. This rating specifies the maximum electrical draw of the unit.

Largest of (C)(1) through (C)(6)

Remember that 220.82(C) is calculating various loads related to heating, cooling, and electric cooking. You'll ultimately use the largest of the loads calculated in sections (C)(1) through (C)(6).

Local Amendments

Always check with your local authority having jurisdiction (AHJ). They may have specific interpretations or amendments to the NEC regarding load calculations.

Good Engineering Practice: While 220.82 allows for a reduced load calculation, ensure the resulting service or feeder is adequate for the dwelling's actual needs. Consider future load additions.By carefully following these guidelines, you can accurately determine the electrical load for your single-family dwelling and ensure a safe and code-compliant installation. Flag for review