When it’s warm outside, air conditioning is what makes indoor life comfortable.
If you’re here because you’re considering installing AC in your Boston-area home this summer — maybe you live in an older home which doesn’t have it, or maybe your current system just isn’t working for you — this guide is all about a newer, energy-efficient method of cooling your home: the ductless mini-split (a.k.a. as a heat pump).
Is your current AC system efficient?
If you’re lucky enough to have Central AC pumping ice cold air throughout your home, you may not give much thought to whether or not your HVAC system is running efficiently. Unless it was installed in the last few years, odds are good that it’s not.
There are a few signs which indicate your cooling system is operating as well as it could.
Your AC unit is running all of the time. There are different reasons why a unit (or part of a unit) might not shut off, but generally it's an indication that the unit isn't able to reach/maintain the desired temperature.
Your energy bills are higher. Energy prices go up from year to year, but if you're using your AC in the same way as last year (same temperature settings at the same time of day), your bills should demonstrate the same usage patterns.
Some rooms aren't getting cool enough. This kind of inefficiency could be caused by old ductwork in central AC systems, or because the unit simply can't work hard enough to compensate for the difference between the outdoor temperature and the desired indoor temperature.
Compare different kinds of home air conditioning
Central AC
- Pros: One AC unit can cool your whole home. Get two AC units to create a multi-zone approach.
- Cons: Requires existing ductwork or its prohibitive to install. Routine maintenance requires professional expertise.
- Energy usage: Compressors and fans running all day and all night consume a lot of electricity.
Ductless Mini-split AC (Heat Pump)
- Pros: A single-zone system is quick and easy to install. A multi-zone system lets you cool each room according to the needs of its occupant. No more fighting over the temperature and no more cooling rooms you’re not using. They come with a remote control or can be easily controlled via an app on your phone.
- Cons: Expensive up front, but many rebates and other financial incentives are available to significantly offset the costs.
- Energy usage: Uses passive energy with minimum energy required to heat and cool efficiently.
- Bonus tip: did you know mini-splits don’t just provide cooling? They also run as energy-efficient heaters during the colder parts of the year! See even more reasons you’ll love switching from central HVAC to a heat pump or contact our licensed mini-split installers for a free quote today.
Portable and Window Unit AC
- Pros: Cheaper and easier to install than Central AC and mini-splits.
- Cons: Noisy and bulky. Limited to one room per unit.
- Energy usage: Each unit uses less electricity than Central AC but way more than mini-split which run on passive heat pumps.
How mini-splits enable multi-zone cooling at home
Mini-splits come as a package of several components: the heat pump (condenser) goes outside, the head (air-handling) unit goes in your room of choice, and they’re connected to each other via flexible conduit, not bulky and rigid ductwork.
Some mini-splits come as a single-zone package. They’re perfect for when you just need to add air conditioning to one room, like a converted attic or a garage you use for working out. Some people with Central AC even put mini-splits in their bedroom so they can keep the room really cool at night without having to cool the rest of the house.
On the flip side, multi-zone systems really unlock whole-home comfort. These systems come with a single unit for outside and as many head units as you need (usually one for each room you want to cool). The outdoor unit (condenser) is much smaller than a traditional AC unit, but multi-zone units could take up more space depending on the size of your home.
Sizing a mini-split AC for your home
There are several things to consider when sizing a unit for your home (or to help you ballpark the costs associated with making the switch to a mini-split).
In addition to how big the room is, you’ll also want to consider how many people are typically in the room, how many south- and west-facing windows the room has (and skylights), and how well-insulated your home is.
Once you’ve sorted out those questions, the last remaining bit is the size of the room you’re cooling. “Sizes” for mini-splits are based on the BTUs they generate. Bigger rooms means more BTUs. Cooling more than one room with a multi-zone system will require even more BTUs.
Example sizing for single-zone mini-splits:
Room size | Recommended capacity |
Up to 150 sq. ft. (10’ x 15’) | 5,000 BTUs |
150-250 sq. ft. (15’ x 15’) | 6,000 BTUs |
250-350 sq. ft. (15’ x 20’) | 7,000 BTUs |
350-400 sq. ft. (20’ x 20’) | 9,000 BTUs |
For a multi-zone mini-split AC system, you’ll want to consider the BTU rating for each unit or zone.
A two-room system may require 30,000 BTUs total, with each indoor unit using 9,000 BTUs and the outside unit using 12,000.
These are rough estimates and actual cooling capacity needed may vary based on the factors discussed earlier.
Comparing the energy usage of Central AC & Mini-Split AC
One of the reasons mini-splits are incredibly popular in Europe is that they have a lot of old housing which lacks central HVAC systems and ductwork (they were often built before these things existed). Just as often, their homes are literally right on top of each other so there’s limited room for bulky AC units outside.
Another reason they’re so widely installed is that they’re incredibly energy efficient. Their low-energy cooling power comes from a few factors:
- They use “heat pump” technology which passively removes heat from inside and moves it outside. (This process works in reverse during the winter, removing heat from the outside air and moving it inside.)
- They are only used in occupied rooms and can be set to “maintenance settings” to keep a room ready to cool down at a moment’s notice.
Mini-splits systems installed in homes with solar power are a double bonus for efficiency.
Heat Pumps vs Air Conditioners
Heat pump technology is a big part of what makes mini-split systems so energy efficient, but there’s more to why you’d pick one cooling solution over the other. Here’s a breakdown on the pros and cons of heat pumps vs AC.
Heat Pump Pros
- Versatility: Heat pumps can both cool and heat your home, eliminating the need for two separate systems.
- Energy efficiency: Heat pumps simply move heat rather than generating it, and so they require less energy to run.
- Cost-effective: In addition to the savings from moving heat vs generating it, mini-splits also save money because you can set each room to a different temperature, and only heat or cool the room you’re using to perfection.
- Less maintenance: Typically, heat pumps require less maintenance than two separate heating and cooling systems.
Heat Pump Cons
- Climate dependent: In regions with harsh winters, like New England, a heat pump might not provide adequate heating and could require a supplemental system.
- Initial cost: The upfront cost of purchasing and installing a heat pump can be higher than that of an air conditioner.
Air Conditioner Pros
- Initial purchase cost: The initial purchase cost of an air conditioner can be lower than that of a heat pump, especially if you already have central HVAC and ductwork installed.
Air Conditioner Cons
- Limited function: Air conditioners only cool. They must be paired with a separate heating system for the colder months.
- Energy consumption: AC units use more energy as they generate cool air rather than transferring existing heat.
- Maintenance costs: Having separate systems for heating and cooling can potentially lead to higher maintenance costs. You also need to have ducts cleaned periodically.
Choosing a mini-split installer
It is possible to install your own mini-split system – if you know what you’re doing. If you don’t have any HVAC experience beyond turning on the thermostat, hiring a licensed HVAC contractor who specializes in mini-splits is highly encouraged.
Here are some important questions to ask your mini-split installer.
In the Boston area, Home Mechanics should be your first call. In addition to our professional expertise and our 5-star rating on Google, we offer free quotes and assistance with obtaining Mass Save rebates and other financial incentives like 0% interest loans.
We proudly serve the Greater Boston communities in Suffolk, Middlesex, and Essex Counties in towns like: Newton, Haverhill, Revere, Arlington, Shrewsbury, and Lowell, Massachusetts.
Take advantage of energy rebates and incentives
The long-running Mass Save program helps Massachusetts residents switch to cleaner, more efficient energy options — like heat pumps instead of air conditioners — by offering incentives like rebates and 0% interest loans.
Home Mechanics is a Mass Save certified Heat Pump Installer. We'll walk you through every step of the process and ensure you get the rebates you qualify for.