Portable vs Window AC Cost Calculator
Why compare portable vs window AC running cost?
Portable air conditioners are flexible and easy to set up, while window units are usually cheaper to run. The tradeoff is often convenience versus efficiency, and the only way to see the real impact is to put numbers on how much electricity each option uses. This calculator lets you compare the energy cost of a portable AC and a window AC with the same cooling capacity, using their Energy Efficiency Ratio (EER), your typical hours of use, and your local electricity rate.
By turning EER and BTU/h ratings into power draw (kW), you can estimate daily, monthly, or seasonal operating cost. This does not tell you which unit is more comfortable, quieter, or cheaper to buy, but it does show how much extra you may pay on your electric bill if you choose a less efficient portable unit over a more efficient window unit.
Key formulas used in the calculator
The calculation is built around the Energy Efficiency Ratio (EER). EER tells you how many British thermal units (BTU) of cooling a unit delivers per hour for each watt of electrical power it draws. Higher EER means better efficiency and lower running cost for the same cooling capacity.
Definitions:
- BTU/h – cooling capacity of the air conditioner in British thermal units per hour.
- EER – Energy Efficiency Ratio, defined as BTU/h divided by power input in watts.
- h – hours of operation per day.
- r – electricity rate in dollars per kilowatt-hour ($/kWh).
From the EER definition, we can get the power draw in watts:
Power (W) = BTU/h ÷ EER
To convert this to kilowatts (kW), divide by 1,000:
Power (kW) = (BTU/h ÷ EER) ÷ 1000
Daily energy use in kilowatt-hours (kWh) is then:
Daily kWh = Power (kW) × h
Finally, daily cost is energy use multiplied by your electricity rate:
Daily cost ($) = Daily kWh × r
Putting everything together in one expression for either a portable or window unit:
Cost = (BTU/h ÷ EER ÷ 1000) × h × r
The same structure applies to both types of units; only the EER value changes.
The formula in MathML form is:
where C is the estimated daily operating cost in dollars.
Interpreting your results
When you use the calculator, you will typically see:
- Estimated daily energy use (kWh) and cost for the portable unit.
- Estimated daily energy use (kWh) and cost for the window unit.
- The difference in cost per day, month, or season between the two options.
Interpret the results as an approximation of how much each unit will add to your electric bill under the conditions you entered. A few practical tips:
- Focus on the difference – The absolute dollar values can vary with weather and usage, but the difference between portable and window estimates gives a good sense of which option is cheaper to run.
- Scale to your time frame – Multiply the daily difference by about 30 for a typical month or by the number of cooling days in your season (for many climates 90–120 days) to get a rough seasonal impact.
- Check the EER inputs – If the portable and window EER values are very close, the cost difference will also be small. If they differ a lot (for example EER 8 vs EER 12), the running cost gap can be large.
- Combine with purchase price – To make a full decision, consider both upfront price and operating cost. A window unit that costs slightly more to buy can pay for itself over a few summers through lower electricity use.
Worked example: portable vs window AC
Suppose you need a 10,000 BTU/h unit to cool a bedroom. You are comparing:
- a portable model with EER = 8, and
- a window unit with EER = 12.
You expect to run the AC for 6 hours each evening, and your electricity rate is $0.13 per kWh.
Portable unit
- Power draw:
Power = 10000 ÷ 8 ÷ 1000 = 1.25 kW - Daily energy use:
1.25 kW × 6 h = 7.5 kWh - Daily cost:
7.5 kWh × $0.13 = $0.975(about $0.98)
Window unit
- Power draw:
Power = 10000 ÷ 12 ÷ 1000 ≈ 0.83 kW - Daily energy use:
0.83 kW × 6 h ≈ 5.0 kWh - Daily cost:
5.0 kWh × $0.13 = $0.65
The portable option costs roughly $0.33 more per day under these assumptions. Over a 90-day cooling season, that is about 90 × $0.33 ≈ $30. Over a 180-day extended season, it would be around $60. The exact number depends on how many days you actually run the unit.
The table below shows how EER alone affects power draw and daily cost for this same 10,000 BTU/h load, assuming 6 hours per day at $0.13/kWh.
| EER | Power (kW) | Daily energy (kWh) | Daily cost (USD) |
|---|---|---|---|
| 8 | 1.25 | 7.5 | $0.98 |
| 10 | 1.00 | 6.0 | $0.78 |
| 12 | 0.83 | 5.0 | $0.65 |
Portable vs window AC: cost and performance comparison
The calculator focuses on electricity cost, but most people also care about noise, installation, and comfort. The table below summarizes common tradeoffs. Keep in mind that individual models can differ.
| Factor | Portable AC | Window AC |
|---|---|---|
| Energy efficiency (EER) | Often lower; many single-hose models lose efficiency due to air leakage and exhaust design. | Typically higher EER at the same capacity, leading to lower running cost. |
| Installation | Simple to set up; uses a window kit and exhaust hose. Good for rentals or non-standard windows. | Requires lifting into a window and securing; may not fit casement or very narrow windows. |
| Mobility | Can be rolled between rooms, although exhaust setup must be moved as well. | Fixed in one window; not designed for frequent moving. |
| Noise | Compressor and fan are inside the room, so noise can be noticeable. | Some noise stays outside; often somewhat quieter indoors at the same capacity. |
| Window impact | Leaves more glass exposed but blocks part of the opening with the vent panel. | Occupies most of the window opening and can reduce natural light. |
| Typical use cases | Spaces where window units are not allowed, unusual windows, or temporary cooling. | Homes and apartments with standard windows where efficiency and cost matter. |
Strategies to reduce cooling cost
Whether you choose a portable or a window unit, you can lower your energy use with a few practical steps:
- Seal air gaps – For portable units, carefully seal around the exhaust hose and window panel to reduce hot air leaking back into the room. For window units, seal around the sides and top of the chassis.
- Prefer dual-hose portables – If you must use a portable AC and have a choice, dual-hose models usually draw less unconditioned air from outside and perform closer to their rated capacity.
- Use fans to improve circulation – A ceiling fan or small desk fan can make a room feel cooler at the same temperature setpoint, allowing you to raise the thermostat a degree or two.
- Cool only the rooms you occupy – Close doors and vents to unused spaces so the AC is not trying to cool your whole home indirectly.
- Shade and insulation – Reduce solar gain by closing blinds on sunny windows and improving insulation where possible. Lower heat load means the AC runs less.
- Use timers and smart controls – Many units have timers or can be paired with smart plugs. Set them to start cooling shortly before you arrive and to turn off automatically overnight or when you leave.
Assumptions and limitations of this calculator
The estimates you see are useful for comparison, but they rely on simplifying assumptions. Keep these points in mind:
- Constant EER – The calculator treats EER as a fixed number. In reality, efficiency changes with indoor and outdoor temperature, humidity, and fan speed. Actual performance may be somewhat better or worse than the rating.
- Standard test conditions – EER ratings are usually measured under laboratory conditions (for example around 95 °F outdoors, 80 °F indoors, and 50% relative humidity). Real homes rarely match these conditions exactly.
- Duty cycle simplification – The calculation assumes the unit is drawing its typical running power for the full number of hours entered. Many thermostatically controlled units cycle on and off, especially at night or in milder weather, which can reduce actual kWh use.
- Electricity rate – The rate you enter is treated as a single flat value. Time-of-use plans, tiered pricing, fees, and taxes are not modeled, so your real bill can differ.
- No maintenance or purchase cost – The tool estimates operating cost only. It does not account for purchase price, installation cost, filter replacement, or repairs.
- Space and climate differences – Room size, insulation, air leakage, and local climate can all change how long the unit has to run. Two homes with the same AC model can see noticeably different bills.
- Dehumidification and comfort – Some units remove moisture more effectively than others, which can improve comfort even at the same temperature. The calculator does not put a value on this.
Because of these assumptions, treat the numbers as estimates that are most useful for relative comparison (portable vs window, or one model vs another) rather than precise predictions of your future utility bills.
Quick FAQ
When does a portable AC make sense despite higher running cost?
A portable unit can be the practical choice when building rules forbid window units, when your windows are not compatible with typical window ACs, or when you need temporary or movable cooling. In these cases, the extra cost on your electric bill may be acceptable compared to the convenience.
Do dual-hose portable models really help?
Dual-hose portable ACs usually perform closer to their rated capacity because they pull outdoor air for cooling the condenser instead of drawing conditioned indoor air out of the room. This can improve effective efficiency and reduce how hard the unit has to work, although they still often lag behind similar window units in efficiency.
Does a higher EER always mean lower bills?
All else equal, a higher EER means lower energy use at the same cooling output, so it tends to lower your bills. However, if a higher-EER unit also has a larger capacity than you need, it may cycle frequently or be used in more rooms, offsetting some of the savings. For comparison, try to look at models with similar BTU/h ratings.
How should I choose values for the inputs?
Most bedrooms use units in the 8,000–12,000 BTU/h range. EER values can often be found on the EnergyGuide label or in the product specifications. Typical residential electricity rates in many areas fall between $0.10 and $0.25 per kWh, but you should check your own utility bill for accuracy.
Note: This explanation is for general informational purposes and uses standard definitions of EER as published by major standards bodies. For precise billing questions, consult your local utility or an HVAC professional.