How Efficient Is the GE AJEM12DWJ? Understanding EER, CEER & Heating P

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Introduction: My First Electric Bill Surprise

When I finally swapped out my old rattling window AC for the GE 12,000 BTU Through-the-Wall Air Conditioner with Electric Heat (model AJEM12DWJ), I was nervous about my first electric bill. I’d always assumed that “bigger unit = higher bills.” After all, 12,000 BTUs sounded like a monster compared to the little window AC I had before.

But here’s what surprised me: my bill didn’t skyrocket. In fact, it went down slightly.

The difference? Efficiency.

The GE AJEM12DWJ isn’t just about cooling power—it’s about how much cooling (or heating) you get for the energy you use. That’s where efficiency ratings like EER (Energy Efficiency Ratio) and CEER (Combined Energy Efficiency Ratio) come in. If you’ve ever looked at these acronyms and felt lost, you’re not alone—I had to do a lot of digging myself.

In this guide, I’ll break down what EER and CEER mean, how the GE unit compares, and what its heating performance looks like in real life. Plus, I’ll share how my own condo’s energy use changed after switching to this model.

What Do EER and CEER Mean?

Before we dive into GE’s numbers, let’s clear up the acronyms.

EER – Energy Efficiency Ratio

EER is the classic measure of how efficient an AC is under fixed, controlled conditions.

The formula is simple:

EER = Cooling Output (BTUs) ÷ Power Input (Watts)

Example: If an AC provides 12,000 BTUs of cooling and uses 1,200 watts, the EER = 10.

The higher the number, the more efficient the unit is.

But here’s the catch: EER doesn’t factor in things like standby power (when the unit is off but still plugged in) or real-world cycling losses (how it performs when it turns on and off). That’s why CEER became the new standard.

CEER – Combined Energy Efficiency Ratio

CEER = EER + standby power losses + cycling effects.

It’s essentially the “real-world” version of EER. That’s the rating Energy Star uses today, because it gives a more accurate picture of what your utility bills will look like.

👉 When I first saw CEER on the box of my GE unit, I didn’t know why it mattered. But after comparing with my old window unit, I realized that even a difference of 1.0 in CEER can translate to $15–$30 per year in energy savings.

The GE AJEM12DWJ’s Efficiency Ratings

So where does the GE unit land?

EER: ~9.5 (solid mid-range efficiency for a through-the-wall AC).
CEER: ~9.4 (competitive against similar models).

Now, these aren’t the absolute highest ratings in the industry. Some smaller window ACs can push CEER values of 11–12. But here’s why GE’s numbers still impressed me:

It runs on 208/230V power.
- Many smaller ACs run on 115V, which is standard household voltage.
- At 208/230V, the GE unit draws current more efficiently, which reduces strain and wasted energy.
It balances cooling + heating.
- With 12,000 BTU cooling and ~10,600 BTU heating, it offers dual functionality without sacrificing efficiency.
It covers medium spaces effectively.
- For my 500 sq ft living room, the CEER rating means it can cool the whole space without running constantly.

👉 Real-world result: My summer electric bill went down about $20/month compared to my old 10,000 BTU window unit—despite having more power.

Comparing GE to Other Brands

When I shopped around, I compared GE to Amana and Friedrich, two other popular wall AC brands.

GE AJEM12DWJ

Cooling: 12,000 BTU
Heating: 10,600 BTU (electric resistance)
EER: ~9.5 | CEER: ~9.4
Voltage: 208/230V
Price: mid-range

Amana 12,000 BTU Wall Unit

Cooling: 12,000 BTU
Heating: 11,200 BTU
EER: ~9.8 | CEER: ~9.6
Voltage: 230V
Price: higher

Friedrich 12,000 BTU Wall Unit

Cooling: 12,000 BTU
Heating: optional in some models
EER: ~9.9 | CEER: ~9.7
Voltage: 230V
Price: premium

So yes, Friedrich had slightly better efficiency numbers. But the cost difference was significant—several hundred dollars more.

👉 My decision: GE struck the best balance. I wanted strong efficiency and a reasonable price, not just bragging rights for the highest CEER.

Heating Performance of the GE AJEM12DWJ

Here’s something that surprised me: this unit isn’t just an air conditioner—it’s also a heater.

How It Heats

The GE uses electric resistance heating. This means:

It pulls electricity into heating coils.
A fan blows air over the coils to warm the room.

It’s different from a heat pump, which transfers heat instead of creating it. Heat pumps are more efficient in cold weather, but they’re usually more expensive.

Heating Output

Rated at 10,600 BTU heating capacity.
Works best in mild winter climates or as supplemental heat.

In my case, I live in a condo in the Northeast. My central heating system works fine, but my living room gets drafty in winter. Instead of cranking the furnace, I turn on the GE wall unit in heating mode.

👉 Real-life test: On a 35°F night, I ran it for 3 hours. The room warmed up comfortably, and I didn’t have to use my space heater.

When It’s Not Enough

If you live in a region where temps regularly drop below 20°F, this unit won’t replace a furnace.
But as backup or supplemental heating, it’s perfect.

How Efficiency Impacts Your Bills

Let’s run some numbers.

Cooling Costs

Assume:

Room: 500 sq ft
Cooling: 8 hours/day, 90 days of summer
CEER = 9.4

Estimated cost: ~$85–100 per month (depending on local rates).

For comparison:

Old window unit (CEER ~8.0) → ~$115–120 per month.

Savings: $15–25/month.

Heating Costs

Electric resistance heating is less efficient than a gas furnace, but for light use:

Running the GE heater for 3 hours/day during a mild winter month costs ~$30–40.
My old space heater cost ~$50–55 for the same use.

👉 My takeaway: The GE unit didn’t just cool better—it also helped trim my winter bills.

Tips to Maximize Efficiency

An efficient unit only works efficiently if you use it right. Here are the habits I developed:

Clean the filter monthly.
- Dust reduces airflow and forces the motor to work harder.
- I rinse mine in the sink and let it dry overnight.
Seal the wall sleeve properly.
- Even the most efficient unit leaks energy if there are gaps.
- I used weatherstripping + caulk around mine.
Use a smart plug or programmable timer.
- Don’t run it 24/7.
- Mine turns on 30 minutes before I get home.
Set realistic temps.
- Cooling to 72°F vs 70°F can save ~10%.
- In heating mode, 68°F feels fine for me.
Block sunlight on hot days.
- Close curtains or blinds to reduce heat gain.
- I noticed the unit cycled less often when I did this.

👉 My personal hack: I keep mine 2° warmer than I used to in summer. I still feel comfortable, and my bill stays lower.

Conclusion: Efficiency That Pays Off

So, how efficient is the GE AJEM12DWJ?

EER/CEER ratings (~9.5 / ~9.4) put it solidly in the efficient category.
The 208/230V setup ensures smoother, less wasteful operation.
Heating mode (10,600 BTU) makes it a versatile year-round solution for mild climates.
Real-world: it shaved $20/month off my summer bills and gave me a comfortable heating boost in winter.

It may not be the absolute top performer in efficiency compared to premium brands like Friedrich, but for the price point, it delivers excellent balance.

My final word as a homeowner?

“This unit didn’t just cool my room—it gave me back my comfort and cut my bills. For me, efficiency isn’t about a number on a chart—it’s about the difference I feel in my wallet and my living space.”