HVAC Zoning Vs. Two Systems

Two popular methods of cooling and heating larger homes are HVAC zoning and using two systems. HVAC zoning either uses several mini-split heat pumps or a central HVAC unit with dampers to cool and heat separate areas at different times. Two systems mean each area in your home has its own dedicated system — for example, your downstairs and upstairs have separate air conditioning units and furnaces.

HVAC zoning is better if you want independent temperature control for each zone or area in your home, but can have higher energy costs and less efficiency. Two systems are more efficient overall and can heat/cool both areas at the same time, but they cost more up-front.

What is HVAC Zoning?

An HVAC zoning system is made up of a series of dampers connected to the home’s central HVAC unit that allows for separate control over specific air ducts going into specific “zones” of the house. It can also be made up of several mini-split heat pumps in each zone.

HVAC Zoning with Central HVAC Unit

These dampers are further separated into two types — manual dampers and automatic dampers — but manual dampers are rarely used anymore.

In this system, each zone is given its own panel that controls how much the dampers open or close in that zone, thereby adjusting the amount of cooling or heating that zone receives.

However, in most cases, your HVAC system will heat and cool each zone one at a time. This limits how quickly it can bring your entire home to a comfortable temperature.

A typical HVAC zoning system can have as little as two zones (as in an first and second floor setup) to as many rooms as the house has for maximum control. For most households, though, four zones are probably the ideal amount for a 2-bedroom, 2-story home—one zone each for the bedrooms and the upper and lower floors.

HVAC Zoning with Mini-Splits

With HVAC zoning using ductless mini-split heat pumps, separate indoor units control the temperature in each zone within your home. Each indoor unit mounts to your wall and works with a single outdoor unit to maintain the desired temperature in your home.

In this setup, each mini-split has its own independent thermostat and can run at the same time as other units in your home. This means you can heat and cool your entire home at the same time. However, since you will need a single mini-split for each zone (and potentially each room), it can quickly cost more than zoning with a central HVAC unit and two systems.

Pros and Cons of HVAC Zoning

Pros of HVAC Zoning

Cheaper purchasing and maintenance cost

Since you will only be buying one HVAC unit for the entire house, there is an immediate benefit in the lower upfront cost of a zoning system compared to a two-system approach. Having only one HVAC system to worry about also means that maintenance is much simpler and less expensive. 

Thermal capacity balance

Every HVAC unit has its own rated thermal capacity, which is the metric that dictates the amount of cooling or heating it is able to push into an area. Having only one system installed in your home means you don’t need to worry about having to calculate the separate thermal capacities of the areas covered by two different systems. 

Centralized controls

Since every zone in the HVAC system connects back to a single HVAC unit, there can be multiple control layers set up with a centralized master control. This is useful for situations like parental controls, where the thermostat in a bedroom zone can be limited by a range set by the master control panel.

With ductless mini-split zoning, each zone has its own thermostat that you can set independently. Most manufacturers allow you to control them with an app all at once or independently.

Cons of HVAC Zoning

Only able to heat or cool one area at a time

Having only one HVAC unit in the whole house means that you can only heat or cool one area at a time. Let’s say you have two zones in your home – upstairs and downstairs. In a properly sized system, your central HVAC system will cool your first floor to start. Then the HVAC dampers will change positions and it will cool your upstairs next. It will keep rotating between the two zones based on the thermostat settings in each zone.

In most cases, this works well and you won’t notice any significant temperature differences or have issues. However, if you need to heat or cool your home quickly, it will take longer than if you have two central HVAC systems for each zone (which could cool both areas at the same time).

On the other hand, HVAC zoning with ductless mini-splits doesn’t have this issue. They can each heat and cool each zone independently as they each have their own blower motor and temperature controls.

Efficiency loss

Depending on the location and setup of your HVAC system, there can be some efficiency loss when channeling cooling or heating to zones that are far away from the HVAC unit due to the length of the ducts that have to be installed.

No redundancy

Having only one HVAC system in the entire home will mean that, if it breaks down, you will have no backup until it’s repaired. The same can be said for ductless mini-split heat pump zoning if all your indoor units connect to a single outdoor unit.

What Is a Two-System HVAC?

A Two-System HVAC setup is exactly as its name suggests: a house with two separate HVAC systems for two major subdivisions, such as two floors. 

With what we already know about the benefits and drawbacks of an HVAC zoning system, you can probably figure out what the pros and cons are for this approach; however, we will still lay them out for you in detail below. 

Pros and Cons of Two HVAC Systems

Pros of Two HVAC Systems

Redundancy

Arguably, the biggest benefit of having two HVAC systems is the redundancy of having an extra HVAC system all set up in case one of the units breaks down. 

This is especially important for homes in very cold areas—you do not want to find yourself in the dead of winter with a broken heater for days, if not weeks on end, as you wait for a repair. 

Independent controls

With two separate HVAC systems, the areas covered by each system can be heated or cooled on their own, providing a different form of granular control that isn’t possible with a zoned central HVAC system. This can reduce battles over the thermostat setting since both areas can have different temperatures.

Better efficiency per system

Because of the shorter duct systems that are required to channel two HVAC systems to two separate areas, each HVAC unit can run more efficiently and use less energy than a single unit doing the same across a larger area. 

Cons of Two HVAC Systems

More expensive to install and maintain

For obvious reasons, purchasing two HVAC systems will be around twice as expensive as a single-zoned HVAC setup. Maintenance will also be similarly expensive, as you will find yourself with multiple systems to both maintain and repair over the years. 

Higher potential energy cost

Even though each HVAC unit in a two-system setup can be smaller than an HVAC zoning system, the two HVAC units will always consume more energy than the single larger unit when both have the same total thermal capacity. This is just a matter of simple physics and is part of the cost of having two separate systems.

Wrap-Up

For the most part, zoned central HVAC systems can heat and cool your home efficiently and are low cost. However, they can’t heat and cool all zones simultaneously and have lower energy bills. However zoned HVAC systems with mini-splits can, but can be far more expensive up-front.

Conversely, two independent central HVAC systems are more efficient and can heat and cool different areas of your home at the same time, but can be more costly to maintain and replace for homeowners.

If you’re not sure which type of HVAC system is best for your home, I strongly recommend consulting with a professional contractor to take a proper look at your home to help you choose an HVAC system that is in line with your cooling and heating needs.