Can You Put A Mini Split Condenser In The Attic?

I have customers ask me if they can put their new mini splits in all kind of weird places. In the garage, on the roof, in a basement, or even under the deck. But not too many ask if they can put it in the attic. Actually under a deck is quite feasible because they are side discharge.

I actually had a customer install his own mini split in a garage. But it was more like a barn on the side of a house. He didn’t care if it added warm air in summer or cold air in winter to his barn like shop area.

Another name for a mini split condenser is “outdoor unit”. There is a really good reason it’s called an outdoor unit. Actually there are several good reasons why a mini split condenser should not be installed in an attic or even in any confined space. Mini split outdoor units need to be outside.

You need to first understand that a heat pump does not create cold air in the cooling mode or warm air in the heating mode. Heat pumps move heat from one place to another. They transfer heat from indoors to outdoors or visa versa.

This article is about whether or not you can put a mini split condenser in an attic. If you want to know more about how a heat pump works I wrote an entire article cleverly describing how they function. You can read it by clicking here. It’s a guided tour and I’m the tour guide.

The main reason a heat pumps outdoor unit has to be outside is to get rid of the hot summer air or cold winter air it has collected from inside your home. When your house gets too warm in the summer your heat pump collects the warm air and moves it outside by the medium of refrigerant.

By placing the condenser in an attic it would be subject to the extremes of weather that attics are so prone to develop. Attics can reach temperatures of around 140 degrees in summer. With a condenser in that heat it would likely not even begin to work. It would have no where to dispel the heat. The heat pumps internal temperatures would rise and it’s high pressure protection device would shut it off.

What Is The AC Unit In The Attic Called?

That is a really good question. If you know you have a piece of HVAC equipment in you attic then it’s got to be an air handler. Air handlers come in various forms. Generally these day they are either gas or electric furnaces.

But how can an AC unit be in an attic and not be a mini split condenser or outdoor unit? That’s because it’s an indoor unit. With cooling only units it’s called an evaporator. With heat pumps you have to call it an indoor unit because in the summer it’s an evaporator and in the winter it becomes the condenser. It’s designed to be indoors or in a confined place.

And to tell you the truth it’s not even an ideal place for an indoor unit. The extreme temperatures are something that it has to compete with. In the summer when the attic is peaking in high temperatures the hot air pours out of the duct system when the unit first cycles on.

Sometimes I leave the fan on constant to keep the room air flowing through the ducts. They are well insulated and only succumb to the heat when left static.

New codes are making it necessary to install all duct work and indoor equipment in conditioned spaces. That means false ceiling and soffits and any configuration that will allow all indoor hvac in the conditioned space. More higher costs and more square footage within the sealed structure.

So by now you may be catching on that an AC unit or a heat pump has to have an indoor and an outdoor unit. When they are in their proper place they can function as designed and last for many years. Put them in an environment that is too hot or too cold and problems will be your companion.

Mini Split Icing Up Outside?

Fact of life is that mini splits ice up in winter, how much depends on climate. Will you be willing to have an iced up mini split in your attic?

Those of us that own heat pumps have icing issues in climates that are sub zero at times. Ice dams form on our roofs and our heat pumps struggle to keep defrosted.

Most mini splits are designed to enter a defrost mode when sensors indicate a freezing problem. Some mini splits can still produce heat in temperatures as low as a minus 15 degrees. A good question to ask if you are looking to buy, will it heat in the dead of my winter temps?

This is a serious consideration. Heat pumps ice up in winter when outdoor temperature plummet near and below freezing. The image below is not a mini split. Not trying to fool you this time. It’s a Trane heat pump outdoor unit in winter packed with ice.

The biggy splits have a defrost cycle in their design that causes them to reverse cycle every so often. This reverse cycle causes the unit to switch to cooling mode and the outdoor coil becomes the hot coil and melts the ice. This one had a broken defrost cycle.

If and when a mini split gets all iced up, where is all the water going to go? Maybe you could devise some kind of drain pan for it to flow to the out of doors or down a plumbing drain. But, that is going to have a tendency to freeze also.

A pan heater or some type of defrost maybe. It’s just a complicated way to go and then there’s the warranty. I don’t know of a manufacturer that would stand behind there warranty if they knew their unit was in an attic.