AC is actually pretty efficient from the point of view of thermodynamics. The Coefficient of Performance of just about any air conditioner or heat pump will be well above 1. That is, Watts of cooling/heating provided per Watt of power. For a purely electrical heater the coefficient of performance is 1. 1 Watt of electricity results in 1 Watt of heating.
If you’re using a heat pump in winter, it’s essentially the same efficiency as using an air conditioner in summer. But, there are differences. For one, if it’s 25C people might feel comfortable. If it’s 35C people are almost certainly using the air conditioner. But if it’s 10 degrees in the other direction, 15C, people might just have warm sweaters on. So, naturally, no heating being used is infinitely more efficient than turning the AC on.
Another difference is that every device in your house generates heat. Your fridge pumps heat from the inside to the outside, meaning it pumps it into your kitchen. Plus the pumps your AC uses to circulate the coolant generate waste heat. Your stove, oven, microwave, kettle, coffee-maker, etc. all generate heat. Your computer, phone, TV, etc. all generate heat. Lamps generate much less heat than they used to. A 100W bulb used to generate 100W of heat, but modern LED lights use only about 4W for the same amount of light – but that 4W still eventually becomes waste heat. That means that in summer your AC needs to dump all that additional heat outside, whereas in winter your heating system has to do less work the more gadgets you have on.
If you have a purely electrical heating system (which are hugely inefficient) every watt your gaming computer uses to generate awesome graphics is a watt your heater doesn’t need to generate to heat the place up. But, in the summer, every watt of heat you generate indoors is a watt of heat your AC unit needs to dump outside.
But, IMO, the bigger deal is that people live in some really cold places. In Fairbanks, Alaska, the daily mean temperature in January is -22.4C. In Phoenix, Arizona the daily mean in July is 35.3. But that means that in Phoenix in the hottest month, the average outside temperature is only about 10 degrees away from a comfortable indoor temperature. Whereas in Fairbanks the average outdoor temperature is a full 45 degrees colder than a comfortable indoor temp. So, my guess is that even if you’re someone who bakes things in the oven daily, even in summer, you have a powerful gaming PC running at up to 1000 Watts, you blow-dry your hair every day, etc. Even then, someone with that lifestyle in Phoneix is probably using fewer watts of overall power (electricity + heating) than someone in Fairbanks.
In the end though, it probably comes down to how you’re generating the power, and how you’re generating the heat. If you live somewhere where your electricity is fully environmentally friendly, then your AC or heating might have zero CO2 cost, unless you include the entire lifecycle of the solar panels, the air conditioners, the heating system, etc. Then the manufacturing process will generate some CO2. But, your use of the system won’t. If you’re heating using heating oil or natural gas, then of course you’re going to generate a lot of CO2 as a result.
AC is actually pretty efficient from the point of view of thermodynamics. The Coefficient of Performance of just about any air conditioner or heat pump will be well above 1. That is, Watts of cooling/heating provided per Watt of power. For a purely electrical heater the coefficient of performance is 1. 1 Watt of electricity results in 1 Watt of heating.
If you’re using a heat pump in winter, it’s essentially the same efficiency as using an air conditioner in summer. But, there are differences. For one, if it’s 25C people might feel comfortable. If it’s 35C people are almost certainly using the air conditioner. But if it’s 10 degrees in the other direction, 15C, people might just have warm sweaters on. So, naturally, no heating being used is infinitely more efficient than turning the AC on.
Another difference is that every device in your house generates heat. Your fridge pumps heat from the inside to the outside, meaning it pumps it into your kitchen. Plus the pumps your AC uses to circulate the coolant generate waste heat. Your stove, oven, microwave, kettle, coffee-maker, etc. all generate heat. Your computer, phone, TV, etc. all generate heat. Lamps generate much less heat than they used to. A 100W bulb used to generate 100W of heat, but modern LED lights use only about 4W for the same amount of light – but that 4W still eventually becomes waste heat. That means that in summer your AC needs to dump all that additional heat outside, whereas in winter your heating system has to do less work the more gadgets you have on.
If you have a purely electrical heating system (which are hugely inefficient) every watt your gaming computer uses to generate awesome graphics is a watt your heater doesn’t need to generate to heat the place up. But, in the summer, every watt of heat you generate indoors is a watt of heat your AC unit needs to dump outside.
But, IMO, the bigger deal is that people live in some really cold places. In Fairbanks, Alaska, the daily mean temperature in January is -22.4C. In Phoenix, Arizona the daily mean in July is 35.3. But that means that in Phoenix in the hottest month, the average outside temperature is only about 10 degrees away from a comfortable indoor temperature. Whereas in Fairbanks the average outdoor temperature is a full 45 degrees colder than a comfortable indoor temp. So, my guess is that even if you’re someone who bakes things in the oven daily, even in summer, you have a powerful gaming PC running at up to 1000 Watts, you blow-dry your hair every day, etc. Even then, someone with that lifestyle in Phoneix is probably using fewer watts of overall power (electricity + heating) than someone in Fairbanks.
In the end though, it probably comes down to how you’re generating the power, and how you’re generating the heat. If you live somewhere where your electricity is fully environmentally friendly, then your AC or heating might have zero CO2 cost, unless you include the entire lifecycle of the solar panels, the air conditioners, the heating system, etc. Then the manufacturing process will generate some CO2. But, your use of the system won’t. If you’re heating using heating oil or natural gas, then of course you’re going to generate a lot of CO2 as a result.