Best HVAC System for 2-Story Houses (Heating & Cooling)


2-story houses often have a problem with the upstairs being too hot. The HVAC system in many 2-story houses is unable to maintain even temperature for the whole house. I thought there must be a better way to heat and cool 2-story houses. So, I did some research.

It turns out that the best HVAC system for 2-story houses is a ductless mini split heat pump system. It allows you to control the temperature of each room in your house independently thereby solving the problem of uneven heating and cooling in 2-story houses.

My family and I live in a 2-story house with a ductless mini split air conditioning system. We never had a problem with the upstairs being too hot. In fact, we decide what temperature we prefer in our bedroom without affecting each other.

Many people are not familiar with ductless mini split heat pumps. Ductless mini splits are incredibly quiet and very efficient. With that said, let's take a look at why ductless mini split heat pumps are the best HVAC system for 2-story houses.

Why Mini Splits are the Best HVAC System for 2-Story Houses?

According to science, cold air will always sink while hot air rises. Hence, 2-story houses often have problems with the upstairs being too hot in the summer when.

Currently, the most common HVAC system in 2-story houses is a central furnace air conditioning unit that does both heating and cooling using propane/natural gas and a split condensing unit.

However, a central furnace air conditioning unit is not a good option anymore with ductless mini splits being able to provide adequate heating during the winter.

Problems with a Central Air Conditioner in 2-Story Houses

Many 2-story houses, especially the old ones are using a single-stage HVAC unit (furnace + AC combo). A single-stage HVAC unit has one thermostat and the thermostat is usually located downstairs.

Air conditioners operate via the temperature signal from a thermostat. If the house is too hot, the air conditioner will provide more cooling power. If the house is too cold, the air conditioner will reduce the cooling power.

Single-Stage Air Conditioner

Now, if you only have one thermostat that is placed downstairs, your air conditioner will provide cooling to your entire house based on the signal given by that thermostat.

We know that the upstairs temperature is different from the downstairs. So, if the thermostat is located downstairs, your air conditioner will only make sure that the downstairs has adequate heating/cooling regardless of the upstairs temperature no matter how you set the thermostat.

So, a single-stage HVAC unit in 2-story houses will almost always have uneven cooling problems.

Two-Stage Air Conditioner

However, some 2-story houses installed a two-stage HVAC unit. A two-stage HVAC unit has two thermostats; one located downstairs and one located upstairs.

2-story houses with a two-stage air conditioner can have two temperature zones; one upstairs and one downstairs. Hence, you can set the temperature of the thermostat to be higher for the upstairs one and lower for the downstairs one.

But, many 2-story houses have a different floor areas for the upstairs and downstairs. Usually, the floor area upstairs is roughly 30% smaller than the floor area downstairs.

Nonetheless, the two-stage central air conditioner is putting the same cooling power for both the upstairs and the downstairs, making the upstairs potentially have overcooling problems.

Fortunately, there are several ways to deal with upstairs overcooling problems. For instance, your HVAC technician may install a bypass to reduce the airflow for the upstairs thereby reducing the cooling effect. Or, your HVAC technician may dump the extra airflow elsewhere in the house.

Anyhow, we can see the system is sub-optimal even with the variable speed type; energy is wasted at unnecessary places. If you are going to sleep in the bedroom, why do you need cooling at downstairs?

So, do we have a heating and cooling system that can solve this problem?

Ductless Mini Split Heat Pump in 2-Story Houses

In my opinion, a ductless mini split heat pump system can solve the uneven cooling problem in 2-story houses. In fact, countries like Malaysia and Singapore have been using ductless mini split air conditioners in almost all 2-story houses for many years.

Here, we install a ductless mini split head (indoor unit) in every bedroom, the living room and the kitchen. Whenever we need cooling in a particular room, we'll just turn on the mini split in that room. Other mini splits in the house don't need to run and we save tons of energy costs with that.

As the name suggests, ductless mini splits don't require a duct. They deliver air straight from the indoor unit. A ductless mini split system basically has two types; a) single-zone and b) multi-zone.

Single-Zone Ductless Mini Split

A single-zone ductless mini split heat pump has one indoor unit and one outdoor unit. Most of the time, single-zone mini splits are more efficient than multi-zone mini splits. However, they have more outdoor units.

People switching from using a central air conditioning system to a ductless mini split system don't entirely accept the fact that there will be 5-7 condensing units hanging outside their house considering the aesthetics of their house.

So, they choose to sacrifice the higher efficiency models and go for the more expensive multi-zone ductless mini split system.

Multi-Zone Ductless Mini Split

A multi-zone ductless mini split heat pump has one outdoor unit but many indoor units. Essentially, the outdoor unit is larger and it is able to accommodate multiple indoor units. Hence, it saves space.

However, multi-zone ductless mini splits are usually less efficient than single-zone ductless mini splits. Furthermore, they are also less reliable compared to single-zone units because the entire house is depending on just one outdoor unit as opposed to multiple individual outdoor units.

Still, if you don't like having many outdoor units, a multi-zone ductless mini split system is a great choice. See my post What is Multi Split Air Conditioner? (Capacity Sharing) to learn more about the difference between single-zone and multi-zone mini splits.

All and all, a ductless mini split system is indeed better than a central furnace air conditioning system when it comes to heating and cooling in 2-story houses.

Advantages of Ductless Mini Splits

When comparing a ductless mini split system with a central furnace air conditioning system, the former seems to be superior to the latter in every aspect. So, let's take a look at the advantages of ductless mini split systems:

1. Temperature Zoning

As mentioned earlier, ductless mini splits enable you to have independent and individual temperature control in each and every room in your house. So, you eliminate the problem of upstairs being too hot in the summer as well as save energy costs by getting rid of unnecessary cooling.

2. High Efficiency

Currently, ductless mini split systems are the most efficient residential HVAC system. A typical ductless mini split heat pump has a SEER rating of 20 which is higher than most central furnace air conditioners and other room air conditioners such as window and portable air conditioners.

High efficiency ductless mini splits have an energy efficiency rating approaching around 30 SEER. You can save a lot of energy costs by using a ductless mini split system.

See my post Most Efficient Mini Splits: Cooling, Heating & Different Types to find out the top efficient mini splits with the highest SEER and HSPF ratings.

3. Quiet Operation

Traditional central furnace air conditioners are known to be noisy. The condensing unit of a central air conditioner can disturb your neighbour during the summer when it is blasting at full power.

On the other hand, ductless mini splits are incredibly quiet. They have inverter technology that enables them to operate at different capacities. As a result, you'll hear less noise and feel more comfortable as the room temperature remain fairly consistent.

Most ductless mini splits run at a noise level around 25 dB for the indoor unit and 50 dB for the outdoor unit. Small units like the 9000 BTU ones only produce 22 dB and 45 dB of noise respectively. See my post What is a Good Noise Level for an Air Conditioner? for more details.

4. Less Maintenance

Ductless mini splits don't require maintenance as much as central furnace air conditioners partly due to the fact that they are not connected to the ductwork in your house. The only maintenance needed for a ductless mini split is regular cleaning which is fairly easy to do.

How Ductless Mini Splits Work in 2-Story Houses?

In most cases, you may choose to have one or two outdoor units that are going to be placed outside your house just like the condensing unit of a traditional split system. Depending on how many rooms you want to be cooled, we're looking at around 5-7 indoor units inside your house.

Next, you'll need to run a set of refrigerant pipes and signal cables from the outdoor unit to each indoor unit. The refrigerant pipes and signal cables will be covered using PVC trunking for protection and aesthetic purposes.

Afterward, you need a condensate drain pipe for each indoor unit to discharge the drain water to the nearest floor trap or elsewhere as per the technician's advice.

Sometimes, we have an AC switch for each indoor unit but it is optional.

Finally, when it's done, you control each mini split via a wireless remote controller. You can control the fan speed, temperature, airflow direction and various other functions depending on the mini split model using the remote controller. You also can set different operation modes and you can learn more about air conditioner modes in my post Air Conditioner Mode Explained: Auto, Dry, ECO & More.

While I was doing my research, I came across a YouTube video that shows a completed mini split system in a 2-story house. It'll give you a good idea of what the final product looks like:

Further to the above video, the position of mini split indoor units is very important. So, I encourage you to read my post Best Place to Put the Mini Split Air Handler and Condenser to learn about various installation options.

Final Thought

Previously, 2-story houses are built with a central HVAC unit because of the heating system that a furnace provides. Now, ductless mini split heat pumps can do very well in low ambient temperatures thereby making them a very attractive choice for 2-story houses.

Many countries in Asia have been using ductless mini split air conditioners in residential and commercial buildings for many decades. In fact, ductless mini split air conditioners are the primary cooling system in most homes.

If you currently have a central furnace air conditioner and you're having uneven cooling problems, consider putting a few ductless mini splits upstairs as a temporary solution before you decided to switch to a ductless mini split system for the whole house.

And, if you're convinced that a ductless mini split system is the best for 2-story houses, check out my post 7 Best Mini Split Air Conditioners (2022 Buyer’s Guide) to gain more insights about which mini splits you should get.

For more about mini splits in general, see my mini split blog achieve.

If you need me to help with your HVAC system, purchase the Email Consultation service.


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Yu Chang Zhen

I enjoy working on air conditioners and ventilation fans because Malaysia is a very hot country.

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