A mini-split condensor unit in a home's attic

Attic spaces are notoriously difficult to heat and cool. At the very top of a building, and often with little insulation, they can get far too hot during the summer and too cold during the winter.

Without proper climate control, attics often sit as unused spaces in homes. But this can be a difficult task. 

They are often too far away from the central HVAC system to receive adequate heating and cooling. 

Homes with boiler heat have no option to cool the attic space in the summer.

Your only two effective options for temperature control in attics are portable units and mini splits. Portable units (window ACs, portable ACs and space heaters) can work in a pinch but they aren’t a permanent solution. 

If you don’t want to spend a lot of time in the attic space, these might work for you. However, if you are looking to turn the attic into a useable space, you’re going to need a better solution.

Is a Mini-Split a Good Option to Heat and Cool My Attic?

Mini splits are a great option for efficiently heating or cooling an attic space.

They don’t use ductwork, are extremely efficient, and are ideal for maintaining strict temperature control or small spaces (like attics). Since this system is a heat pump, it can provide both heating and cooling.

A few considerations need to be made before doing an attic install but this is going to be your most effective heating and cooling option available.

What Is a Mini-Split?

Mini-splits are heating and cooling systems that can be installed in your home to maintain living areas at comfortable temperatures.

Ductless mini splits are heat pumps. This means they work by heat transfer and basically pump heat from one area to another.

Like a central air conditioner, they are comprised of two main units:

  • The condenser, which is located outside of your home
  • The indoor head, which is an air handler that is mounted to an exterior wall inside your home

The condenser and the indoor head are connected together by copper lines where refrigerant circulates between them.

The exterior component of a ductless mini-split attached to a home's exterior brick wall

Refrigerant is pumped around the system to transfer heat from the cool side of the system to the warm side. Refrigerant is a unique gas with the right combination of thermodynamic properties to effectively absorb and transfer heat energy around the mini-split.

On cooling mode, it takes heat from inside and expels it outside. On heating mode, it runs in reverse and finds heat in the outside air and pumps it inside.

Mini split heat pumps can work in temperatures as low as -15°F. Even though it might seem like there is no heat in the outside air, the heat pump can find it.

Mini-split heat pumps move heat rather than generate heat directly as an electrical resistance heater would. This makes them both eco-friendly and cost-effective. Despite being an entirely electric system, they are inexpensive to operate.

Insulate Before Installing a Mini-Split

Mini-splits can be very effective at heating and cooling, but before jumping to that solution, it’s essential to ensure your attic is adequately insulated.

Attic spaces are difficult to heat and cool because they are subjected to greater temperature extremes during the year.

This exposure is partly because their surfaces (walls and ceilings) form the barrier between the outdoor elements and the living space and don’t benefit from the insulating effect of adjoining rooms.

They also get the sun’s full glare in the summertime, which heats the external-facing side of these surfaces and throughout. So by 10 am on a sunny summer day, you’ll feel the heat of the sun coming through the wood of your roof unless you have the proper insulation in place.

You have a few main options when it comes to insulation. They include:

  • Rigid foam board insulation
  • Fiberglass insulation
  • Spray foam insulation

Rigid Foam Board Insulation

Stacked sheets of polyisocyanurate foam board insulation

Rigid foam board comes in panels that can easily be cut to size and are placed between the joists of your roof or wall studs.

It has very good R-values (typically 3.8-5 per inch of thickness) and is easy to work with.

Fiberglass Insulation

Fiberglass insulation typically comes in rolls, or batts, which are easy to transport and install. It’s also available in loose-fill form, but you need a mechanical blower to install loose-fill fiberglass insulation.

Fiberglass insulation being installed in the underside of a home attic ceiling, showing a beige fiberglass batt

Fiberglass insulation has lower R-values than rigid foam board insulation, but you can increase its insulating effect by placing additional layers.

Spray Foam Insulation

As its name suggests, spray foam insulation is sprayed into place between the joists in your home.

Foam insulation has a very high R-value and can serve as an effective seal, which is particularly important if you want to prevent warm air from escaping through your attic during the winter, and keep the cold, conditioned air inside during summer.

A picture of spray foam insulation covering the floor and wood studs in a wall.

For more information on the different types of insulation available and the pros and cons of each, why not read our article comparing rigid foam board and fiberglass insulation?

Use Blinds to Keep the Sun Out

It sounds obvious, but a lot of the unwanted heating of your attic space during the summer months will come from the sun.

Drawing curtains during the day’s heat or using angled blinds to keep out the worst of the sun’s rays while still allowing daylight through is a great way to cut down on solar gain.

Sometimes doing this alone is enough to prevent temperatures from becoming oppressive but attic spaces have a lot going against them, so you are likely to need alternative solutions.

Installing a Mini-Split in Your Attic

Because mini splits don’t require ductwork, they can be easy to install. But attics pose a couple of difficulties.

For starters, If the condenser is set on the ground, you will likely need to add to the lineset for it to reach the attic. If you mount the compressor higher up on your house with a bracket, then it will be more difficult to service.

You will need to get power to the indoor head unit as well as a drain. These aren’t an issue for an HVAC professional, but they will probably cost a little more in materials.

Generally, the indoor head should be mounted high on the wall in a location where it can reach the most space. The attic can be a little tricky, but you should be able to find space for it. 

If there is absolutely no space on the wall, you can opt for a floor-mounted unit. They typically take up a little more space, but they will work just as well.

All in all, an attic install shouldn’t be too difficult, but no two attics are alike so your HVAC contractor might have to get a little creative to find the best solution.

Final Thoughts

Installing a mini split in your attic is a great option to increase your usable home space, but it can be a little tricky to get the right indoor unit and add enough line to reach the top story of the home. 

This is not a problem for HVAC professionals but it isn’t something you should try to do yourself.

Not only will you need to climb a very high ladder, but you’ll need to add gas to the mini split system if you have to add line. And there is no way to do that without the adapters, gauges, and refrigerant. 

If you’re thinking about a mini split in your attic, you should factor in costs of having it professionally installed.

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