What Size Heat Pump Do I Need? How to Match Tonnage to Home Size

By Mike Sanders, HVAC Expert

Choosing the right size heat pump is one of the most important decisions you'll make for your home comfort—and your energy bills. Go too small and your system can’t keep up. Too large and it’ll short cycle, wasting money and wearing out faster.

So how do you know if a 3-ton heat pump—like the Goodman GLZS4BA3610—is right for your home? It starts with understanding tonnage, BTUs, square footage, and what actually affects your home’s heating and cooling load.

This guide will walk you through everything you need to know to match your heat pump size to your home size—accurately, affordably, and confidently.

🔧 What Does “Tonnage” Mean in HVAC?

Nope—it’s not weight.

In HVAC, 1 ton = 12,000 BTUs/hour of heating or cooling capacity.

So a 3-ton heat pump like the Goodman GLZS4BA3610 can move 36,000 BTUs/hour.

💡 Think of it as how much heat the system can remove (cooling) or deliver (heating) per hour.

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🧠 Why Correct Sizing Matters

📎 Why HVAC Sizing Is Critical – Building America

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📊 General Rule of Thumb by Square Footage

⚠️ These are just rough guidelines. Actual sizing depends on more than just square footage.

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🏠 What Really Impacts Heat Pump Sizing?

1. Climate Zone

• Hot, humid zones (FL, TX): may need larger systems

• Cold zones (MN, NY): require heating backup or higher capacity

📎 DOE Climate Zone Map

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2. Insulation & Windows

• R-value of attic, wall, and floor insulation

• Single-pane vs double-pane glass

• Leaky vs well-sealed windows and doors

Poor insulation? Add 0.5–1.0 tons more capacity.

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3. Ceiling Height

• 8 ft ceilings = standard load

• 10 ft+ ceilings? Increase capacity by 10–20%

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4. Sun Exposure

• South-facing glass = higher cooling load

• Lots of shade = lower demand

Solar heat gain can increase tonnage by 0.5 tons or more in some homes.

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5. Occupancy & Lifestyle

• People, pets, and appliances = internal heat

• High appliance use or home gyms = more cooling demand

📎 Manual J Load Factors Explained

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📐 What Is Manual J (And Why It Matters)?

A Manual J load calculation is the gold standard for sizing a heat pump. It accounts for:

• Orientation

• Construction materials

• Air leakage (ACH)

• Internal loads

• Weather data

📎 Manual J Software from ACCA

Most utility companies or HVAC pros can provide this analysis—and it’s required for rebates in many areas.

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🏠 Is a 3 Ton Heat Pump Right for Your Home?

Let’s break it down with examples.

✅ 3 Ton Is Likely a Good Fit If:

• Your home is 1600–1900 sq ft

• You live in a temperate or mild climate (Zone 3–5)

• You have average insulation and double-pane windows

• Ceilings are 8–9 feet

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⚠️ You Might Need More Than 3 Tons If:

• Your home is over 2,000 sq ft

• You have vaulted ceilings or poor insulation

• You live in a hot climate (Zone 1–2)

• You have large glass exposures or an older build

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❌ You Probably Need Less Than 3 Tons If:

• You live in a compact, newer home <1500 sq ft

• You’ve done insulation upgrades

• You’re in a mild climate like Pacific Northwest

• Ductless or zoned systems supplement main system

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🧰 How the Goodman GLZS4BA3610 Performs

It’s an ideal balance of performance and price for homes in the 1600–2000 sq ft range—especially in Zones 3–5.

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💸 What Happens If You Oversize?

Oversizing leads to:

• Short cycling

• Poor humidity control

• Increased wear and tear

• Higher maintenance costs

• Duct noise and pressure issues

✅ Avoid this by running a proper Manual J + duct static pressure test

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📦 What Happens If You Undersize?

Undersizing results in:

• Constant runtime

• Cold/hot rooms

• High utility bills

• Inadequate heat on cold days

📎 ASHRAE Equipment Sizing Guidelines

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🔧 When to Add Auxiliary Heat Strips

If your home is in a cold climate (Zones 6–7) or uses electric-only heat, a 3-ton system may need heat strips:

• Add 5–10 kW strips to maintain temp during freezing spells

• Works automatically with Goodman systems when sized correctly

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📊 Compare: 2.5 Ton vs. 3 Ton vs. 3.5 Ton

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🧠 Mike’s Pro Tips

1. Don’t trust square footage alone—always include ceiling height, insulation, sun, and layout.

2. Run a Manual J—or at least a BTU estimate based on your region and build year.

3. Consider zoning if your home has hot/cold rooms or two stories.

4. Match your air handler for proper airflow—no mismatches!

5. Get ductwork evaluated—undersized ducts = high static pressure = low performance.

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🏁 Final Thoughts from Mike Sanders

“Sizing a heat pump isn’t just math—it’s comfort science. If your home’s around 1,700–1,900 sq ft in a temperate zone, a 3-ton system like the Goodman GLZS4BA3610 is a rock-solid pick. But if you want true comfort and savings, get a load calc. Don’t guess—measure.”

In the next topic we will read about: Cold Climate Ready? How Goodman Heat Pumps Perform in Northern Winters