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Is it possible to buy a climate-friendly air conditioner? We asked an expert

Residents of Mass Pike Towers in Boston rely on window air conditioners.
Residents of Mass Pike Towers in Boston rely on window air conditioners.David L. Ryan/Globe Staff

The heat is rising, you’re feeling sweaty, and you’re contemplating whether it might be time to invest in air conditioning. But if your gut tells you that A/C isn’t the most eco-friendly option, you’re correct. A/C devours electricity, can leak potent greenhouse gasses, and is linked to warmer outside temperatures, which can, in turn, lead to more power use.

It’s a toxic feedback loop.

So what steps can you take to make a purchase that reflects your concerns about climate change? For advice, we asked Kurt Roth, a senior fellow at Boston University’s Institute for Sustainable Energy, and the energy systems team leader at the university’s Fraunhofer Center for Manufacturing Innovation.

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I guess the first thing I’d ask is if we should even be having this conversation. Should we be using air conditioning at all?

That’s kind of like asking should we be heating your house or driving your car. People can die from overheating and cold.

So what can we do to use air conditioning and not destroy the planet?

The first thing generally you want to do is reduce the amount of cooling you need as much as possible in order to reduce the energy load on your unit. That means insulating your roof and walls well so you have less cooling required and air sealing your home as well, so there’s less air leaking and less work for your air conditioner to do. Removing incandescent light bulbs can also help, as they generate a lot of heat, and you can lose up to 20 to 30 percent of the heating or cooling your system provides through duct leakages, so that’s another thing to address.

You also want to think about sizing the unit correctly. Energy Star has a calculator on its website, and the Air Conditioning Contractor’s Association has what’s called a Manual J calculation, which should be used for sizing central air conditioners.

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What if I want to purchase a window unit?

Purchase an Energy Star unit. They have a tier of products which they deem “most efficient.” And MassSave has incentives that you’ve already paid for in your bills. Take advantage of that.

A lot of the really efficient units now work on variable speeds. The fan and compressor can vary their speeds to better match more closely the amount of cooling you need to be doing. A lot of these newer, more advanced units will measure humidity and have a dehumidification mode.

What if I’m looking to install central air?

One of the biggest things that can be done in terms of cooling system from a climate perspective is actually what can be done to the heating system. In Massachusetts we have hot spells that last a few days but generally we don’t use too much cooling. A lot more energy is spent on space heating. If you have an existing A/C or central air unit or are looking to put something in, you can put in a heat pump that is optimized for cold climates. If you’re going to put in an air conditioning unit and you already have ducts it’s pretty easy to put in a heat pump to replace it.

And what if I don’t have ducts?

If you have a boiler, ductless mini-split heat pumps are really nice, compact devices that can be wall-mounted or installed outside the home. They’re very quiet and very efficient as well. MassSave has very generous incentives if you have oil or propane heat.

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So once you’ve got the air conditioning installed, a lot still hinges on how you use it, right?

Right. You have to operate it smartly, upping the temperature when you’re not going to be there. The efficiency of a cooling system typically decreases as it gets hotter, and the bigger the difference is between the inside temperature and the outside temperature, the lower the efficiency. If you cool your house earlier in the day and kind of ride through the hot times, the house will be more efficient overall.

What role can connected devices like smart thermostats play?

Smart thermostats can save you on the order of 15 percent for residential customers. Another thing is the demand response program. Using connected thermostats, it notes when the grid is most stressed and lets utility companies reduce the stress on the grid. That has a greenhouse gas benefit as peak demand will often require the use of big gas turbines, which can be more carbon intensive.

What about maintenance?

If your heat exchanger gets leaves and debris in it, it’s not as efficient. You have to keep the outdoor air coils clean. Another significant problem is the refrigerant charge for a central air unit. If the amount of refrigerant goes lower, it reduces capacity and it takes more energy to cool the same amount of house. Having a professional check the refrigerant charge is not a bad idea.

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So what are you doing this summer to keep cool?

I have a two-family home, and I’m up here on the third floor with a ductless mini-split. It’s great.

This interview has been condensed and edited.



Janelle Nanos can be reached at janelle.nanos@globe.com. Follow her on Twitter @janellenanos.