Is 11,800 BTUs Enough? How to Size Your Wall AC for Maximum Comfort

🏠 Introduction: Mike’s Sizing Dilemma

When Mike decided to replace his aging window AC, he knew he wanted something more permanent, efficient, and quieter. After weeks of research, he landed on the Amana 11,800 BTU 115V Through-the-Wall Air Conditioner with Remote — a compact yet powerful unit made for medium-sized rooms.

But like most homeowners, Mike had a lingering question:

“Is 11,800 BTUs really enough for my space?”

This guide walks you through exactly how Mike figured it out — from measuring his living room to accounting for insulation, ceiling height, and even climate — so you can do the same before choosing your Amana wall unit.

---

⚙️ 1️⃣ Understanding BTUs — The Basics Behind Cooling Power

Before crunching numbers, Mike had to understand what a BTU (British Thermal Unit) actually meant.

• Definition: One BTU is the amount of energy needed to raise (or remove) the temperature of one pound of water by one degree Fahrenheit.

• In AC terms: It measures how much heat your air conditioner can remove from a room per hour.

So, an 11,800 BTU AC can theoretically remove 11,800 BTUs of heat every hour.

Mike compared it to horsepower for cars:

“BTUs are like your AC’s horsepower — too little, and it struggles; too much, and it wastes fuel.”

❄️ Undersized vs. Oversized Cooling

• Undersized Unit: Runs constantly, can’t reach target temp, raises energy bills.

• Oversized Unit: Cools too quickly, shuts off before dehumidifying, leading to clammy air.

A right-sized unit runs efficiently, maintains steady comfort, and lasts longer.

📘 Read more: Energy.gov – Room Air Conditioners

---

📐 2️⃣ Step One: Match BTUs to Room Size

Mike started with the classic rule of thumb:

“You need about 20 BTUs of cooling per square foot.”

That means:

Mike’s living room measured 15 ft × 30 ft = 450 sq. ft., placing him right in the 11,000–12,000 BTU range — perfect for the Amana 11,800 BTU model.

📘 Reference: ASHRAE Cooling Load Guidelines

---

🧱 3️⃣ Factor 1: Insulation and Construction Quality

Not all homes are built alike. Mike’s was a 1990s two-story with decent insulation — R-13 in the walls, R-30 in the attic. If you live in an older home or one with thinner walls, your cooling load rises quickly.

Example:
Mike’s 11,800 BTU unit effectively covered up to 495 sq. ft. in his well-insulated home — but in an older, drafty house, the same unit might comfortably cover only 400 sq. ft.

📘 Learn more: Energy Star – Proper AC Sizing

---

🌞 4️⃣ Factor 2: Sunlight and Window Exposure

Sunlight makes a huge difference. Mike’s west-facing windows received afternoon sun, adding heat gain.

The U.S. Department of Energy suggests adjusting for sunlight like this:

• Sunny rooms: Add 10% BTUs

• Shaded rooms: Subtract 10%

So, for Mike’s space:

11,800 BTUs × 1.10 = ≈13,000 BTUs required

He balanced that by keeping thermal curtains drawn during peak hours and installing low-E window film, effectively restoring his 11,800 BTU balance.

📘 Source: DOE – Cooling Efficiency and Windows

---

👥 5️⃣ Factor 3: Number of Occupants

The more people in a room, the more body heat generated.
Add 600 BTUs per extra person beyond two occupants.

Mike’s setup usually included him and his wife — two people — so no adjustment needed. But during summer gatherings, when 4–5 guests were around, he noticed the AC working harder.

His fix? He turned the fan speed to high and dropped the thermostat 2°F in advance of company arriving.

---

🍳 6️⃣ Factor 4: Appliances and Electronics

TVs, gaming consoles, and lighting can add several hundred BTUs of heat.
Mike’s living room housed a 65-inch TV, cable box, and soundbar — about 500 BTUs of extra load.

If your space doubles as a kitchen or office, account for these:

• Kitchen with oven/stove: +4,000 BTUs

• Home office with computers: +1,000 BTUs

Mike decided his 11,800 BTU Amana was sufficient since his cooking area was separate.

---

🧭 7️⃣ Factor 5: Ceiling Height

Most BTU charts assume 8-foot ceilings. If your home has taller ceilings, increase your capacity proportionally.

Mike’s was 9 ft, so he multiplied by a 1.125 adjustment factor:

11,800 BTUs × 1.125 = ≈13,275 BTUs effective requirement

He knew he was slightly under that, but thanks to strong insulation and moderate climate, the Amana handled it easily.

📘 Reference: Energy Star – Room AC Sizing Rules

---

🌡️ 8️⃣ Factor 6: Local Climate and Region

Climate plays a massive role in cooling demand. Mike lives in Ohio, where summers hit the mid-80s°F with moderate humidity — a “medium load” region.

If you live in:

• Hot, humid areas (Texas, Florida): Add 10–15% BTUs

• Dry, temperate areas (Colorado, Oregon): No adjustment

• Northern regions (Maine, Minnesota): Subtract 10%

📘 Climate Data: NOAA Climate Zones Map

---

🏡 9️⃣ Mike’s Final Load Calculation

Let’s put it all together:

Verdict? The Amana 11,800 BTU unit came close enough — and his real-world performance confirmed it.

---

🔍 10️⃣ Testing the Real-World Results

Mike ran several tests after installation.

🌬️ Cooling Speed

Starting at 80°F indoor temperature, the Amana cooled the space to 72°F in 10 minutes on high fan speed.

💧 Humidity Control

Maintained 45–50% relative humidity, comfortable without feeling damp.

🔇 Noise

Measured 55 decibels at 6 feet — quieter than his refrigerator.

⚡ Power Usage

Monitored via Kill A Watt meter: ~1.1 kW per hour average draw.

He found his monthly cooling cost dropped by around 18% compared to his old 10,000 BTU window unit.

📘 Reference: EPA Energy Efficiency Ratings Explained

---

🧊 11️⃣ Why Sizing Matters Beyond Comfort

A properly sized unit doesn’t just cool better — it lasts longer and saves money.

Benefits of correct sizing:

• ✅ Longer compressor lifespan

• ✅ Consistent humidity control

• ✅ Lower energy use

• ✅ Quieter operation

• ✅ Better indoor air quality

Mike’s takeaway:

“The right BTUs mean your AC doesn’t have to overwork or short cycle. Mine runs steady, quiet, and efficient.”

📘 Read: Energy Saver – Room AC Efficiency Guide

---

🧰 12️⃣ Tools & Methods Mike Used

Here’s what helped him decide confidently:

• Laser tape measure: For precise room sizing

• Smartphone BTU calculators: Verified math

• Energy.gov estimator: Adjusted for climate zone

• ASHRAE table: Used for load corrections

• DIY comfort log: Tracked temperature changes

📘 Try: Carrier Cooling Load Estimator

---

💡 13️⃣ Signs You’ve Chosen the Wrong Size

⚠️ Undersized Unit

• Runs continuously

• Never reaches target temperature

• Feels humid

⚠️ Oversized Unit

• Turns off quickly (short cycles)

• Feels cold but sticky

• Noisy compressor on/off

Mike once helped a neighbor who bought a 15,000 BTU model for the same room size — it cooled too fast, leaving the air clammy and uncomfortable. After comparing notes, he realized his own correctly sized 11,800 BTU unit performed better overall.

---

🔌 14️⃣ The Efficiency Sweet Spot: EER, CEER & SEER2

EER (Energy Efficiency Ratio):
BTUs ÷ power draw (watts). Higher = better.
Amana’s 11,800 BTU unit has an EER of ~10.6, meaning it delivers 10.6 BTUs of cooling for every watt consumed.

CEER (Combined Efficiency):
Includes standby and fan energy — even more accurate.
Mike’s unit’s CEER of 10.3 means great energy performance for a wall model.

SEER2 (Seasonal Efficiency):
Applied mainly to central and mini-split systems, but gives perspective on yearly performance.

📘 Learn more: Energy Star Efficiency Ratings

---

🧩 15️⃣ Comparing Alternatives

Mike chose the 11,800 BTU because it balanced power with efficiency — and worked on standard home voltage (no electrician needed).

---

🧠 16️⃣ Common Sizing Mistakes Mike Sees Homeowners Make

1. Basing on square footage alone (ignoring sun exposure and height)

2. Buying “bigger is better” units that short-cycle

3. Ignoring insulation or window count

4. Overlooking regional climate

5. Placing AC too low or behind furniture

His advice:

“Spend 10 extra minutes planning your room layout — it’ll save you years of inefficiency.”

---

🧭 17️⃣ How Climate Zones Affect Cooling Power

The U.S. is divided into five climate zones, and each changes how much cooling your space needs:

Mike used the DOE zone map to confirm his BTU math matched real-world needs.

📘 Climate Reference: NOAA Temperature Trends

---

🧾 18️⃣ The Cost Breakdown: Equipment + Energy

Upfront Cost:

• Amana 11,800 BTU Wall AC: ~$800–$900

• Wall Sleeve + Trim Kit: ~$100–$150

• DIY Installation: Free (Mike did it himself)

Energy Cost:
At 1.1 kW/hour and $0.14/kWh average:

1.1 × 8 hrs/day × 30 days × $0.14 = ~$37/month

That’s cheaper than running central air in just one zone.

---

🧼 19️⃣ Maintenance Affects BTU Efficiency

Even the right-sized unit performs poorly if neglected. Mike learned that dirty filters can reduce efficiency by 10–15%.

Seasonal checklist:

• Clean filter monthly

• Vacuum coils every 3 months

• Inspect drain for blockages

• Seal any wall air leaks annually

---

🌬️ 20️⃣ Beyond BTUs: Airflow & Circulation Hacks

Mike added a few finishing touches to enhance comfort:

• Tower fan near hallway: Circulates cooled air

• Reflective curtains: Reduces solar load

• Weatherstripping: Prevents hot air infiltration

“I realized BTUs are just part of the equation. Airflow makes the difference between cool and comfortable.”

---

🧰 21️⃣ Bonus: When to Step Up to Multi-Zone or Mini-Split

If your space exceeds 600 sq. ft., or you’re cooling multiple rooms, consider:

• Through-the-wall dual setups (two 11,800 BTUs on opposite sides)

• Mini-split systems for zoned comfort

But for single spaces like living rooms, dens, or master bedrooms, Mike insists:

“You’ll rarely need more than what Amana’s 11,800 BTU model delivers.”

---

🧩 22️⃣ Mike’s Verdict: Was 11,800 BTUs Enough?

After a full year of use, Mike’s verdict is clear:
✅ Yes, 11,800 BTUs was exactly right.

Results:

• Consistent 72°F even during 95°F days

• Quieter operation than expected

• No moisture buildup or short cycling

• Energy savings of 15–20% annually

“I used to think bigger meant better. Turns out, balanced is best.”

---

🧠 23️⃣ Final Takeaways: Mike’s Sizing Rule of Thumb

1. Measure your space first. (L × W × H ÷ 500 × 12,000 = BTUs baseline)

2. Adjust for sunlight and people.

3. Factor in insulation and ceiling height.

4. Pick a unit with EER ≥ 10.

5. Don’t oversize — it hurts comfort and humidity.

When in doubt, choose a slightly smaller, more efficient model rather than an oversized one.

---

In the next topic we will know more about: Airflow & Noise: What to Expect from Amana’s 11,800 BTU Model