Quick Hits

⚡ Quick Hit: Bucket #2 — Heating & AC (Part 2)

NEC Article 120 — “Load Calcs Won't Kill You” 🔌⚡

Episode 29 — 120.82(C)(4)–(6) Heating & Air-Conditioning Loads

🪣 BUCKET #2 CONTINUES

In Episode 28, we started working through the six possible heating and air-conditioning selections under 120.82(C).

We covered:

1️⃣ AC / cooling

2️⃣ Heat pump without supplemental heat

3️⃣ Heat pump with supplemental electric heat

Now let's finish the list.

OPTIONS 4–6

And there's an important lockout rule at the end.

🔥 OPTIONS 4 & 5 — ELECTRIC SPACE HEATING

Straight electric space heating gets a demand factor based on the number of separately controlled heating units.

The more independently controlled units you have, the greater the permitted demand reduction.

4️⃣ FEWER THAN 4 UNITS

If there are fewer than four separately controlled heating units:

65% of the nameplate rating(s)

is used.

5️⃣ FOUR OR MORE UNITS

If there are four or more separately controlled heating units:

40% of the nameplate rating(s)

is used.

🧠 WHY THE DIFFERENCE?

Think about diversity.

If a home has multiple separately controlled heating units, it's less likely that every unit will be operating at maximum output simultaneously.

Fewer units:

65%

More units:

40%

More separately controlled heating units → greater diversity → lower calculated demand.

🏠 QUICK EXAMPLE

Imagine a dwelling has four separately controlled electric heating units with a combined nameplate rating of:

20 kVA

Because there are 4 or more separately controlled units:

20 kVA × 40% = 8 kVA

Calculated load = 8 kVA

The number of separately controlled units matters.

🔒 OPTION 6 — THE SPECIAL CASE

Now we get to the unusual one.

Some electric heating systems are expected to operate:

Continuously at full nameplate value

Examples include:

Electric thermal storage heating

and other qualifying systems expected to operate continuously at their full nameplate rating.

For these systems:

100% OF NAMEPLATE

is used.

🚨 THE OPTION 6 LOCKOUT

Here's the part you really want to remember:

If the system qualifies under Option 6, it:

CANNOT ALSO BE CALCULATED UNDER OPTIONS 1–5.

This isn't:

"Calculate all six and pick whichever is smallest."

Option 6 has its own lane.

🔒 Option 6 = locked out of the other five selections

🧠 THE SIX OPTIONS — COMPLETE

Selection

Basic treatment

1️⃣ AC / cooling

100% nameplate

2️⃣ Heat pump, no supplemental heat

100% nameplate

3️⃣ Heat pump + supplemental heat

100% compressor + 65% supplemental heat*

4️⃣ Electric heating

65% if fewer than 4 separately controlled units

5️⃣ Electric heating

40% if 4 or more separately controlled units

6️⃣ Continuous full-nameplate heating

100% nameplate

*Subject to the applicable simultaneous-operation provision.

⚠️ IMPORTANT

For the ordinary selections, the applicable calculations are compared and the largest calculated kVA is used.

Option 6 is different: a system qualifying under that selection isn't also calculated under the other five selections.

🎯 TEST YOURSELF

A home has electric thermal storage heating expected to operate continuously at its full nameplate rating.

Per 120.82(C)(6), can this system also be calculated under Option 4 or Option 5 for comparison?

A) Yes — always compare all options

B) No — Option 6 systems can't be calculated under any other selection

C) Only if it's cheaper for the homeowner

D) Yes — but only Option 5

👇 What's your answer?

✅ ANSWER

B) NO

If the heating system qualifies under 120.82(C)(6), it cannot also be calculated under the other five selections.

🔑 REMEMBER:

OPTION 6 = ITS OWN LANE

Don't calculate it under Option 4 or 5 and then choose whichever result you prefer.

🪣 BUCKET #2 — COMPLETE

We've now covered all six heating/AC selections.

🌡️ Bucket #2

Heating & Air-Conditioning ✅

Selections 1–3: Episode 28

Selections 4–6: Episode 29

The next question is:

What's the biggest applicable heating/AC calculation?

That's the number that ultimately matters for this bucket under the optional method.

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🧭 QUICK HIT NAVIGATION

← Back to Article 120 Quick Hits

← Episode 28 — Heating & AC (Part 1)

→ Episode 30 — Bucket #3: EVSE & Putting It Together

🏠 120.82 SERIES

Episode 25: Welcome to Part IV

Episode 26: Who Gets to Use This Shortcut?

Episode 27: Bucket #1 — General Loads

Episode 28: Bucket #2 — Heating & AC (Part 1)

Episode 29: Bucket #2 — Heating & AC (Part 2) ← YOU ARE HERE

Episode 30: Bucket #3 — EVSE & Putting It Together

⚠️ EDUCATIONAL NOTICE

This Quick Hit is an educational explanation based on the author's understanding of the NEC. It is not a substitute for the official NEC, applicable local amendments, manufacturer instructions, or the determination of the Authority Having Jurisdiction (AHJ).

Always verify the requirements applicable to your specific installation.

The National Electrical Code® and NEC® are registered trademarks of NFPA. JoshTheSparky.com is not affiliated with, sponsored by, or endorsed by NFPA.