Mini-Split Heat Pump FAQ: Your Questions Answered

Do you have questions about mini-split heat pumps?

If so, you’ve come to the right place. This article is jam-packed with helpful information for anyone looking to learn more about these heating and cooling systems.

Whatever your question, chances are you’ll find an answer either here in this article or in our archive of mini-split articles.

Can a Generator Run a Mini-Split?

Mini-splits are a very convenient way of heating and cooling your home, but what can you do if the power goes off?

The obvious thing to do is hook up your mini-split to a generator, but you must be careful if you’re considering doing this because you risk damaging your heat pump if you use the wrong type of generator.

Many generators produce “dirty power,” a generalized term describing electricity that exhibits characteristics such as frequency variations, voltage fluctuations, and surges.

If you are running a standard lighting circuit, dirty power will cause lights to flicker, and it’s no big deal. However, dirty power can damage a mini-split, which contains sensitive electronics that don’t fare well when voltages spike.

That’s why it’s essential to use the correct type of generator.

If your generator doesn’t produce clean power, it might not immediately fry your mini-split’s inverter board, but it increases the risk of failure a few months down the line or the following season.

The right type of generator to use is inverter style, which produces much cleaner power.

Your options range from a large generator that kicks in seamlessly when the power goes off so that you don’t even notice, to models where you need to go out to the shed and connect things up.

Prices and lifestyle requirements vary, and you need to choose a solution that’s right for you.

Can You Install a Mini-Split Under a Window?

Installing the outdoor condenser below a window will not affect its functionality. However, it could obstruct your view through the window if it is too close.

Most HVAC installers will choose to mount the condenser elsewhere if possible, just to keep things looking neat, tidy, and out of sight.

Can a Mini-Split Be Mounted Vertically?

No. The air handlers must be mounted horizontally. They have condensate drains that will leak if you try to mount the unit vertically. 

If the wall-mounted indoor air handler doesn’t suit your tastes, you can opt for a ground-mounted unit or a recessed ceiling cassette. But you cannot hang your wall-mounted mini split in a vertical position.

Can a Mini-Split Be Plugged into an Outlet?

No. They need their own dedicated breaker from the electrical panel.

Most heat pumps run on a 220-volt supply, although some smaller models are available that run on 110 volts. Standard household electrical outlets in the US provide 110V, which would seem just right for one of the more modest systems that only require 110V.

Any attempt to connect your mini split to a standard outlet is a very bad idea. If these units were meant to be plugged into the wall, they would come with electrical plugins. And they do not.

This would be a massive code violation.

One of the requirements of NEC is that all significant fastened-in-place electrical appliances, including mini-splits, must be on their own dedicated circuit.

This stipulation means you can’t just plug your system into an outlet, even if the voltage is correct, because it would not comply with the NEC.

The main reasons for this requirement are twofold:

• First, the dedicated circuit for your mini-split must have a disconnect box to allow power to be cut off during repair and servicing work.
• Second, if you put a heat pump on the same circuit as other household appliances, you risk overloading the circuit.
  Mini-splits draw a lot of amps, particularly when they start up, although this settles down under steady-state operation. During the start-up phase, you might find your circuit breakers frequently tripping if someone is drying their hair with an electric hair dryer on the same circuit.

Can a Mini-Split Cause Mold?

High humidity creates optimal conditions for mold to grow. Mini-splits running in cooling mode help dehumidify the air, and some units have a special “dry” setting to optimize dehumidification.

However, if you live in a particular humid environment, you may need a dedicated dehumidifier.

In humid conditions, it’s possible mold will grow in the unit itself. This problem occurs when you don’t clean your filters regularly. Dust and other debris can build up on the coil fins, providing an ideal substrate for moisture to gather and mold to grow. So, while mini splits don’t cause mold, they can harbor it under certain circumstances.

To combat this, simply clean your filters regularly. And if you notice dirt embedded in the coils, have an HVAC tech out to clean them.

Can I Leave My Mini-Split on All the Time?

Yes. This is exactly how they are meant to be used. Simply set the temperature and forget about them.

Modern units use inverter-driven compressor technology, which allows them to precisely modulate their output to the required level of heating and cooling.

Setting the temperature and leaving them run is more energy efficient for the system than if you are constantly turning it on and off with the remote. These systems have their own built-in smart technology to regulate their speed for maximum efficiency while maintaining indoor temperature settings.

Can You Cover a Mini-Split?

No. Do not cover these systems during the winter. Heat pumps work differently than traditional air conditioners. The outdoor unit on a heat pump runs on both heat and cooling mode. If you cover it, your system will not work and could become damaged in the process. 

If you are worried about damage from snow and icefall, you could make an overhang that will protect the mini split and still allow it adequate airflow for operation.

Can You Install a Mini-Split Without a Vacuum Pump?

Purging the refrigerant lines on a heat pump system is vital to ensure there is no air or moisture in the unit, which can reduce the efficiency of your system and cause the compressor to overheat and fail prematurely.

Vacuum pumps remove everything from the line set before opening the valves and adding refrigerant. Vacuum pumps are also a vital part of the installation process to check for leaks. If the system does not hold a vacuum, there is a leak somewhere that will vent refrigerant into the atmosphere when the valves are opened.

Some manufacturers have started offering DIY mini-splits that don’t require any specialist tools to install.

As an HVAC professional, I would recommend going with one of the big three trusted mini split brands: Mitsubishi, Fujitsu, or Daiken. And have it installed by a licensed professional.

Can You Mix and Match Mini-Split Components?

No. Part of what makes mini splits so efficient is their built-in smart technology that allows the outdoor and indoor units to be in constant communication with each other.

If you need a new air handler or condenser, you will need an exact replacement for the system to function.

Can You Oversize a Mini-Split?

Yes you can. Bigger is not better in the HVAC world. Units must be sized correctly for proper operation.

While mini-splits can modulate their output and turn down their capacity to match the heating and cooling requirement, there is a minimum below which they cannot turn down further.

The result of installing a system that is too large is that, rather than turning down and operating at a low-speed steady-state, it must turn off completely to avoid overshooting the temperature setpoint. This is called short cycling. It will decrease your system’s efficiency, make it difficult to maintain indoor temperature and will decrease the lifespan of your unit.

Can You Paint a Mini-Split?

There’s no reason you can’t paint the outside of an air handler to match the walls in your home. That being said, the outside of the air handlers are made of plastic and you may need to search around for a suitable paint.

If you choose to do this, make sure you don’t get paint on the inside mechanisms of the unit.

Here’s a great “how-to” video showing how to paint an air handler unit:

Do I Need an Air Handler in the Bathroom?

In many cases, there is no need to install a mini-split in a bathroom or other small spaces in the home, such as hallways. The heating and cooling effect by units serving larger rooms in the same zone should be sufficient if the air circulation is adequate.

If you need heating or cooling in your bathroom and you don’t have the wall space for an air handler, you can get a ducted air handler for the area. These are less common but they are readily available.

Will a Mini Split-Heat or Cool My Garage?

Yes. Mini splits work great for most garages. Unlike traditional garage heaters, mini splits can provide both heating and cooling, making garage spaces more usable throughout the year.

Their lack of ductwork makes them easy to install in garage spaces and workshops.

However, your garage should be insulated before installing your new mini split or you will lose a significant amount of energy through the walls.

Why Does a Mini-Split Heat Pump Leak Water?

The most common cause of water leaking is a blocked condensate drain. Mini splits drain water that they have removed from the air as a normal part of their operation.

On occasion, this drain can get clogged with debris. It’s an easy fix and one you can likely do yourself. 

If your mini split is freezing up (ice on the coils and lineset), you could see water leaking out as it melts. You can read more about that in the next section.

Why Do Mini-Splits Freeze?

If your mini split is freezing in the summer (on cooling mode) you either have air restriction somewhere or the system has a refrigerant leak. If you see ice buildup on the coils or on the lines, first check that your filters are clean.

If the filters are clean, then go outside and check the outdoor condenser for debris. If you find grass clipping, cottonwood seeds or leaves blocking the coils, wash them out with a garden hose.

If that doesn’t take care of the problem, call a HVAC company because you likely have a refrigerant leak. If your mini split is freezing during the winter (on heating mode), it simply needs to run the defrost cycle. Most mini splits will have sensors to detect this and will remedy the problem themselves by running in reverse for a few minutes.

This is a normal part of operation and nothing to be concerned about. If the mini split is not defrosting itself adequately, it’s time to call a professional and find out what’s wrong.

Final Thoughts

These are just some of the most common questions we see about mini splits. If your question hasn’t been answered here, please check our archive of mini-split articles for more information about these flexible, efficient, and convenient systems.

If you are considering installing a mini split in your home or garage, your best bet is to talk to a few local HVAC companies and get their opinions.

Most HVAC contractors will come out to your property and do a walk through when they give you an estimate and will be happy to answer any questions you have specific to your home.