SEER is a seasonal average, so real running cost varies with weather, set temperature and how the unit is used. Uses your tariff for the electrical input only.
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This calculator works out what an air conditioner costs to run. Enter its cooling capacity in kW, its SEER (seasonal energy efficiency ratio), the hours it runs each day, the cooling days per year and your electricity tariff, and it returns the electrical input in kW and the cost per hour, per day and per cooling season.
It is for installers and customers who want a realistic figure for the electricity a unit will use, rather than a guess. Because modern air conditioning is efficient — it moves several units of heat for every unit of electricity — the running cost is usually far lower than people expect, and being able to show that helps close a sale.
The key is the SEER. Cooling capacity is the heat the unit removes, but the electricity it draws is the capacity divided by the SEER. The calculator handles that, then applies your running hours, cooling days and tariff to give hourly, daily and seasonal costs.
Input (kW) = capacity ÷ SEER; Cost/day (£) = input × hours × tariff (p/kWh) ÷ 100; Cost/season = cost/day × cooling days
SEER is a seasonal ratio of cooling output to electrical input, so the electricity the unit draws is its cooling capacity divided by the SEER. A 3.5 kW unit at a SEER of 6.5 draws about 0.54 kW. Multiplying that input by the running hours and the tariff (and dividing by 100 to convert pence to pounds) gives the daily cost, and multiplying by the cooling days per year gives the seasonal cost.
Type the unit's cooling capacity in kW and its SEER from the data sheet or energy label. The default SEER of 6.5 is typical of a modern inverter split — a higher SEER means lower running cost for the same cooling.
Enter how many hours a day the unit actually cools, defaulting to 6. Inverter units modulate rather than run flat out, so use the hours it is genuinely working, not just switched on at the wall.
Enter the number of cooling days per year, defaulting to 120. In the UK, cooling demand is concentrated in the warmer months, so a full year of use is unrealistic for most installations.
Type the electricity unit rate in pence per kWh from the customer's bill (default 27). The calculator shows the electrical input in kW and the cost per hour, per day and across the cooling season.
SEER is a seasonal average, so the real cost varies day to day. It bundles together mild days when the unit sips power and hot days when it works hard into a single efficiency figure. That makes it good for estimating a season's cost, but any individual day can be higher or lower depending on the weather, the set temperature and how hard the unit has to work.
The figures cover the electricity the unit draws for cooling only. They do not include the standing charge, and they assume the running hours and cooling days you enter reflect real use. A unit left on all day at a low set point will cost far more than one used sensibly for a few hours when the room is occupied.
Small changes in set temperature make a real difference. Every degree lower you ask the unit to hold increases the load and the running cost, so setting a comfortable 24°C rather than a chilly 19°C can cut the bill noticeably. Use the seasonal figure to have that conversation with customers who worry air conditioning will be expensive to run.
SEER is a seasonal average, so real running cost varies with weather, set temperature and how the unit is used. Uses your tariff for the electrical input only.
Less than most people expect, because the unit is efficient. A 3.5 kW split at a SEER of 6.5 draws about 0.54 kW, so at 27 p/kWh it costs roughly 15p an hour to run. Over a 6-hour day that is about 87p, and across a 120-day cooling season around £105 — but it depends heavily on the tariff, the hours and how cool the room is kept.
SEER is the seasonal energy efficiency ratio — the cooling a unit delivers divided by the electricity it uses, averaged across a cooling season. A SEER of 6.5 means the unit moves 6.5 units of heat for every 1 unit of electricity, which is why air conditioning is cheaper to run than its cooling capacity in kW might suggest. Higher SEER means lower running cost.
Divide the cooling capacity by the SEER to get the electrical input in kW. A 5.0 kW unit at a SEER of 6.5 draws about 0.77 kW. Multiply that by the hours it runs and your tariff in pence per kWh (then divide by 100) to get the cost — the calculator does all of this for you.
Because efficiency changes with the weather. On a mild day the unit barely works and runs very efficiently; on a hot day it works hard and efficiency drops. SEER averages this across a whole cooling season, so it gives a more honest running-cost estimate than a single peak-condition efficiency figure would.
No. The calculator covers the cost of the electricity the unit uses to cool — its input kW multiplied by your unit rate. The daily standing charge is a fixed fee you pay regardless of usage, so it is not part of the air conditioner's running cost. Take the unit rate from a current bill, as tariffs change.