The Sizing Checklist — Mike’s Pre-Install Walkthrough for Every Customer

👋 1️⃣ Why Every Job Starts with a Walkthrough

When I pull up to a house for a new HVAC install, the first thing I do isn’t grab a wrench — it’s grab my tape measure.

Most companies show up ready to sell. I show up ready to listen and measure. Because in my book, the math starts at the mailbox.

“I never size a system from a desk — I size it from the front porch.”

I’ve seen too many jobs go wrong because someone “matched” the new unit to the old one. That’s like buying new shoes based on your favorite pair from 10 years ago — the fit’s probably changed.

A few summers back, a homeowner told me,

“Mike, the old 3.5-ton cooled okay.”

When I ran the load calc, I found the home only needed 2.5 tons. The old unit was blasting cold air, short-cycling, and leaving the place clammy.
We swapped it, tightened the ducts, and their power bill dropped 22%.

Guesswork doesn’t save money.
Math does.

That’s why every job starts with a full pre-install sizing walkthrough. I gather all the info before we even think about lifting equipment.

Here’s the checklist I use — every single time.

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📏 2️⃣ Step 1 — Measure the Space (Inside and Out)

Before any numbers go into a Manual J calculator, I measure the house like I’m building it myself.

Zillow square footage? Not good enough.
Blueprints? Outdated.
I measure what the system actually conditions.

My Field Tools

• Laser distance meter

• Digital manometer

• Hygrometer (for humidity readings)

• iPad or phone app with load calc software

What I Measure

• Conditioned floor area

• Ceiling height

• Window area & direction

• Exterior wall construction

• Insulation depth & material

• Orientation (north, south, east, west)

• Shade coverage — trees, overhangs, awnings

Each detail changes the load.
A west-facing living room with big windows can add 3,000 BTUs or more on its own.

“I don’t care what the tax record says your house size is — I care what air your system has to condition.”

🔗 Reference: Energy Vanguard — What Is Manual J?

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🧱 3️⃣ Step 2 — Inspect the Ductwork

Most problems I find aren’t with the equipment — they’re in the ductwork.

The ducts are the lungs of the system.
If they’re leaking, kinked, or undersized, your shiny new system will suffocate.

What I Check

• Flex runs pinched or longer than 25 ft

• Metal trunks sized correctly

• Return air undersized (very common)

• Insulation levels (R-6 minimum, R-8 preferred)

• Duct leakage at seams and boots

Then I measure static pressure with my manometer.

A system over 0.7 in w.c. is like trying to breathe through a straw. It’ll rattle, whistle, and burn out motors faster than anything.

“You can buy the best condenser in the world, but if your ducts choke it, you just paid for a Ferrari that can’t leave first gear.”

🔗 Reference: ACCA — Manual D Duct Design Guide

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💨 4️⃣ Step 3 — Identify Heat Gains and Losses

Next, I perform a quick heat gain/loss audit.

It’s part detective work, part physics class. Every opening, appliance, and attic choice affects comfort.

I Look For

• Window type (single, double, low-E)

• Direction of major glass walls

• Roof color & pitch (dark = hotter attic)

• Attic ventilation (ridge vs gable)

• Door gaps & weather stripping

• Appliance heat (kitchens, server closets)

A home office with three monitors and a PC tower can add 500 BTUs/hr. Multiply that across rooms and you can easily over- or under-size by a half-ton if you ignore it.

“Every lightbulb and laptop counts. I’ve seen a home office add half a ton of load.”

🔗 Reference: Energy.gov — Heat Gain and Loss Factors

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🧮 5️⃣ Step 4 — Verify the Current System

Before tearing out the old unit, I learn what it’s telling me.

I check:

• Suction & liquid line temps

• Superheat/subcooling

• Return vs supply ΔT (temperature split)

• Runtime length

• Noise & airflow pattern

• Thermostat accuracy

If the old system never runs more than 10 minutes a cycle, it’s oversized.
If it runs forever and never catches up, it’s undersized or starved for air.

“If the old system never ran long enough to pull moisture, I know where to start — it’s not the refrigerant, it’s the math.”

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⚙️ 6️⃣ Step 5 — Run the Load Calculation (Manual J)

Now comes the fun part — crunching numbers.

I plug all those field readings into my Manual J app. It calculates sensible (temperature) and latent (humidity) loads for every room.

Then I show homeowners the printout.

“Your house doesn’t need a 3-ton system — it needs a 2.0-ton with strong duct design and humidity control.”

This one page often changes everything. It proves we’re not guessing.

🔗 Reference: ACCA — Manual J Guidelines

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🧰 7️⃣ Step 6 — Match the Equipment (Manual S)

Once the load’s set, I match the system with Manual S. That means choosing real equipment that performs within ±5% of the load at local design temperatures.

Here’s an example from a recent job:

System Chosen:
Goodman 2.5-Ton 13.4 SEER2 R-32 Condenser (GLXS3B3010)

At 95°F outdoor / 75°F indoor, it delivers ≈ 28,500 BTU — right on target for a 2.4-ton load.

Paired with a variable-speed air handler, this setup dehumidifies better and runs quieter.

“I didn’t upsell. I right-sized — and that’s what really saves the customer.”

🔗 Reference: Goodman — SEER2 Standards Overview

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💨 8️⃣ Step 7 — Balance the Air (Manual D)

Equipment chosen? Great. Now we make sure the air actually gets where it’s needed.

I calculate duct sizes using Manual D and the measured static pressure.

Targets:

• 400 CFM per ton

• Static ≤ 0.5 in w.c.

• Equal supply/return balance

• R-8 insulated attic ducts

• ≤ 2°F room-to-room variance

Example:

After balancing, static dropped from 0.62 → 0.46 in w.c. — perfect.

“Comfort isn’t built in the backyard — it’s built in the ductwork.”

🔗 Reference: DOE — Air Duct Design & Testing

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🧊 9️⃣ Step 8 — Talk Efficiency & Comfort Options

Once the sizing is dialed in, I give homeowners choices, not pressure.

We talk about:

• R-32 vs R-410A refrigerants

• SEER2 ratings and long-term savings

• Variable-speed vs single-stage blowers

• Smart thermostats (Ecobee, Honeywell T10)

• Dehumidifiers or zoning for comfort balance

I explain it in plain English — energy, noise, maintenance.

“My job’s not to upsell — it’s to make sure you know what you’re paying for and why.”

🔗 Reference: ENERGY STAR — High-Efficiency HVAC Guide

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🧮 🔟 Step 9 — Confirm and Educate Before Install Day

No surprises. Before install day, I review everything with the homeowner:

Checklist Recap

• Load summary by room

• Equipment match (Manual S)

• Duct adjustments (Manual D)

• Predicted runtime & humidity range

• Filter size and MERV rating

• Warranty and maintenance schedule

Then I hand over a printed report. Transparency builds trust.

“When you see the math, you trust the result.”

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📋 11️⃣ The Homeowner’s Version of Mike’s Checklist

If you’re hiring an HVAC contractor, here’s your cheat sheet:

“A good installer welcomes these questions. A bad one dodges them.”

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🧩 12️⃣ Mike’s Real-World Example — The 2.5-Ton Success Story

Remember that Tennessee ranch?
1,400 sq ft, south-facing, older ductwork.

We followed this exact checklist:

1️⃣ Measured every room (14 × 8 ft ceilings)
2️⃣ Inspected attic ducts — one return undersized
3️⃣ Ran Manual J → 28,800 BTU (2.4 tons)
4️⃣ Selected Goodman 2.5-ton R-32 SEER2
5️⃣ Balanced airflow to 1,000 CFM
6️⃣ Installed Ecobee smart thermostat

Results

• Humidity dropped from 62% → 48%

• Runtime increased from 12 → 28 minutes

• Power bill fell $34 per month

• Noise cut in half

“Right-sized systems run longer, quieter, and cheaper — and they make me look like a genius.”

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💬 13️⃣ Mike’s Wrap-Up Philosophy

Sizing isn’t a mystery. It’s a process — and processes never lie.

If your installer skips steps, you’ll pay for it in comfort and energy bills later.
When I train younger techs, I tell them:

“Measure twice, install once, and let the math do the selling.”

Because good sizing sells itself. When a homeowner feels even temperature, quiet airflow, and low humidity — that’s your best advertisement.

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🧩 14️⃣ Internal Link Strategy

Buy this on Amazon at: https://amzn.to/47dm4yJ

In the next topic we will know more about: Square Footage vs. System Size — The Real Math Mike Uses on Every Job