Quick Hits

⚡ Quick Hit: Bucket #2 — Heating & AC (Part 1)

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

Episode 28 — 120.82(C) Heating & Air-Conditioning Loads

🪣 BUCKET #2: HEATING & AC

We've filled Bucket #1 — General Loads.

Now we're moving into:

🌡️ HEATING & AIR-CONDITIONING

And this bucket works differently.

There isn't just one calculation.

There are:

SIX POSSIBLE SELECTIONS

But here's the important part:

You don't add all six together.

You determine which selections apply to the dwelling, calculate each applicable option, and then use the largest calculated kVA.

🧮 THE BIG RULE

Think of the process like a competition:

OPTION 1

Calculate it.

OPTION 2

Calculate it.

OPTION 3

Calculate it.

OPTION 4

Calculate it.

OPTION 5

Calculate it.

OPTION 6

Calculate it.

Then:

🏆 THE LARGEST ONE WINS

Only the largest applicable heating/AC load is used for this bucket.

🌡️ OPTIONS 1–3

Let's start with the first three selections.

1️⃣ AIR-CONDITIONING / COOLING

Calculate:

100% of the AC/cooling equipment nameplate rating(s)

If this is the applicable selection, the full nameplate load is used.

2️⃣ HEAT PUMP — NO SUPPLEMENTAL HEAT

For a heat pump used without supplemental electric heat:

100% of the heat-pump nameplate rating

No supplemental heat means there's no additional electric-heating component to include under this option.

3️⃣ HEAT PUMP + SUPPLEMENTAL ELECTRIC HEAT

For a central heat-pump system with supplemental electric heat:

100% of the heat-pump compressor

PLUS

65% of the supplemental electric heat

That's the basic calculation for this selection.

⚡ THE SIMULTANEOUS-OPERATION EXCEPTION

Here's the important twist.

If the heat-pump compressor and supplemental electric heat are physically prevented from operating at the same time:

You don't have to add both loads together.

Why?

Because the electrical system isn't expected to supply both loads simultaneously under that arrangement.

🧠 THINK:

Can they run together?

➡️ Yes: apply the applicable combined calculation.

Can they NOT run together?

➡️ They don't need to be added together.

🎯 TEST YOURSELF

Per 120.82(C)(3):

If a heat-pump compressor is prevented from operating at the same time as the supplemental electric heat, what must be done?

A) Always add both together regardless

B) They do NOT need to be added together

C) Use only the supplemental heat value

D) Use only the compressor value at 50%

👇 What's your answer?

✅ ANSWER

B) They do NOT need to be added together

When the heat-pump compressor and supplemental electric heat are prevented from operating simultaneously, they don't need to be added together for this calculation.

🔑 REMEMBER

No simultaneous operation = don't automatically combine the loads.

🧠 120.82(C) SO FAR

Selection

Calculation

1️⃣ AC / Cooling

100% of nameplate

2️⃣ Heat pump, no supplemental heat

100% of nameplate

3️⃣ Heat pump + supplemental heat

100% compressor + 65% supplemental heat*

*Subject to the applicable simultaneous-operation provision.

⚠️ And remember:

You don't add Options 1–3 together.

You're comparing the applicable selections and ultimately using the largest calculated kVA.

🪣 BUCKET #2 ISN'T DONE YET

We've covered:

🌡️ Heating & AC — Part 1

Selections 1–3 ✅

But there are still:

Selections 4–6

to work through.

Those are coming next.

📚 KEEP EXPLORING

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🧭 QUICK HIT NAVIGATION

← Back to Article 120 Quick Hits

← Episode 27 — Bucket #1: General Loads

→ Episode 29 — Bucket #2: Heating & AC (Part 2)

🏠 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) ← YOU ARE HERE

Episode 29: Bucket #2 — Heating & AC (Part 2)

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.