Are split air conditioning systems more efficient than central AC?

Which is more efficient, a split air conditioning system or a forced air central AC unit? We need to replace our central air conditioner and I’m wondering if a minisplit air conditioner is a better option.

Answer from Green Energy Efficient Homes

Both central air conditioners and ductless minisplit air conditioners have a Seasonal Energy Efficiency Rating (SEER), and if you look at the range of systems available in both classes, you’ll find that the best ductless minisplits have a slight edge on efficiency over the most efficient central air conditioning systems. For example, the best SEER ratings on central air conditioners for some of the major brands are 21 (Lennox, Carrier), 20 (Trane, Bryant) and 18 (York), while the best ductless minisplit ratings are 23 (Gree, Sea Breeze), 22 (Friedrich, Lennox, Trane) and 21 (Mitsubishi Mr. Slim).

Ductless minisplit systems are a great way to go if you don’t already have central ductwork. With the help of a qualified electrician you can easily install one yourself, and if you have a traditional two- or three-storey home you really only need the indoor units on the top floor, since (A) heat tends to build up most on the top floor where the ceiling touches the attic, and (B) cold air falls.

A ductless minisplit system has one or more evaporator units that are installed in particular rooms, and a single condenser unit located on an outside wall or on a flat roof. The refrigerant circulates between the evaporator units and condenser unit in pipe less than an inch thick, so you just need a few small holes in your walls to install a system. Compare that to installing HVAC ducts throughout your home and you can see why ductless minisplit systems are popular as a first air conditioning system.

One of the main efficiency benefits of ductless minisplits is that, because you can install multiple indoor units, you can control each unit separately, even though there is just one condenser unit doing the actual cooling work. For example, you can have a unit installed in each bedroom and one in the main living area, and keep the bedrooms cool at night when you’re asleep, but leave the units off during the day when the bedrooms are empty; meanwhile keep the living area cool when you’re up and about, and turn the living area unit off when you’re in bed. For a bedroom especially, a ductless minisplit system can cool very quickly, so as long as you turn it on a quarter hour before you’re ready to head to bed, you’ll be comfortable without spending a lot of money keeping an empty bedroom cool.

Most ductless minisplits can operate in fan-only mode as well, which I recommend for warm but not insufferably hot nights; a gentle (or powerful) breeze from your bedroom unit can provide enough air circulation to keep you cool, at a much lower cost than the actual cooling. As long as your attic hasn’t built up a huge amount of heat through the day, this is often all you need to stay comfortable overnight.

Before you invest in any large air conditioning system, though, you’d be well advised to find less energy intensive techniques for staying cool. Making sure you have high efficiency windows, good wall and attic insulation, and adequate attic ventilation, all make a huge difference; and if you’re careful about keeping the windows closed and the blinds drawn during the day, and running window fans at night when the temperature drops a little, you can often get by even on the hottest days with no AC at all.

We had central air when we moved into our Toronto home, but we hardly ever used it (thanks to some of the above techniques), and we ripped the system out before a major remodel. Now we have no air conditioning at all (central or window), but when the HVAC technician came to do our annual service maintenance, I asked him about air conditioning systems, and he recommended installing just a ductless minisplit rather than a full central AC system. He said that for our well-insulated, 1,500 square foot home, all we really needed was a single evaporator unit in the upstairs hallway. That means a significant savings for us in three ways: money, since for a given SEER rating a ductless minisplit is quite a bit cheaper than the central AC equivalent; energy, obviously; and garden space, since the condenser for a central AC unit will take up a big chunk of garden space. The ductless minisplit condenser can just be mounted on the wall in our driveway.

For more information…

Here are some pages where I cover related topics that can help you keep cool in summer:

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