Homes are becoming more sophisticated and connected; a home’s heating system is no different. “By zoning an HVAC system, homeowners can access customized temperature control and energy efficiency,” said Mike Bauman, senior technical support specialist at Resideo.
The concept of zoning isn’t new; it has been around for a while within the industry, but it isn’t talked about enough in residential applications. “We do see zoning in our industry as most modern and efficient hydronic floor radiant system’s zone. It’s there. But the interesting thing is when we flip the conversation and ask contractors installing a furnace or air conditioner how many are zoned, the conversation is a little different,” explains Dick Foster, president of ZoneFirst.
In the zone
HVAC zoning refers to dividing a home or building into specific areas, each with its own thermostat control to regulate temperature independently. “When talking to a customer about the possibility of zoning, explain it the same way you would explain a light switch.
In a home, a customer wouldn’t want one light switch that controls the whole home. You flick the switch, and the whole home is lit. That isn’t functional or the best. You want control in each room. Zoning is no different,” explains Foster.
In terms of benefits to zoning, comfort is at the top of the list, “With a properly designed zoning system, the heat pump can cycle off completely when a particular zone is not calling for heating or cooling,” adds Foster.
When broken down into single-stage, two-stage, or modulating equipment, it is almost always advantageous to zone using multi-stage technology. This is one of the main advantages of zoning a heat pump as it is typically two stages, explains John Brown, chief engineer at EWC Zone Controls. “An inverter heat pump can be more cost-efficient than running a fossil fuel furnace, depending on the kilowatt rate versus the gas, liquid propane, and oil rate cost in a given area of the country.”
It is important to remember that each individual system requires its own solution. A single-zone system would be more effective for a smaller space, whereas for larger homes, it might be better suited for a multi-zone approach.
It should still be noted that a single-stage heat pump can still be zoned. “However, multi-stage and, in particular, modulating heat pumps lend themselves quite well to zoning,” explains Brown. “You can satisfy a single zone’s demand using the low BTU capacity of a modulating system or the first stage of a multi-stage heat pump. With a single-stage system, full BTU capacity is brought online for a single zone demand, which consumes more energy.”
Why a heat pump?
The answer to the question of which technology is better suited for zoning, heat pumps or furnaces, might be surprising to some. “Traditional furnaces benefit from zoning, but they are not as flexible when compared to a heat pump,” explains Foster. A zoned air-to-air heat pump can be considered more energy efficient compared to a zoned furnace system because of the variable capacity operation. “Modern air-to-air heat pump systems often have a variable capacity operation, allowing the heat pump to adjust its output to match each zone’s heating or cooling demands more efficiently,” explains Foster.
Additionally, since a heat pump’s heat transfer process occurs primarily through refrigeration circulation, “Zoning allows the heat pump to operate at a reduced capacity since only selected zones are conditioned at a given time,” explains Foster. It is worth noting that the energy efficiency benefits of zoning a heat pump or furnace system can vary depending on the specific equipment, system design, and usage pattern of a home.
The right duct
One of the most significant factors in an adequately zoned system is the quality of the ducts. “For a ducted zoning system, ideally, whoever is doing that layout would like a main trunk for each zone so that they can put a single damper in that zone,” explains Bauman.
Brown adds, “Duct quality, more specifically duct sizing, is the biggest factor that affects the performance of any HVAC system, whether it’s zoned or not. Undersized ductwork results in high static pressure, noise complaints, poor airflow complaints and may affect the refrigeration circuit.”
Older technology, like permanent split capacitor (PSC) indoor blower motors, can’t compensate for under-sized ductwork like a variable speed blower motor can. “Thus, the PSC motor drops and loses CFM as the static pressure of the HVAC system increases above 0.5 inches of water column,” explains Brown. When speaking specifically on duct sizing for heat pumps versus furnaces, there really is no difference between the sizing, explains Brown.
Dampers and airflow
Dampers are a crucial element to a zoned system, but they “don’t need to be in a specific angle or position,” explains Foster. “While there isn’t a specific angle or position that is needed, there are different control strategies that are debated. One topic of debate is when a zone is active, should the damper be 100 per cent open? Or should it modulate towards close as the zone gets close to satisfying?”
Brown states that, in his opinion, each damper should be open from the beginning of the heat or cool demand to its end. “Some control strategies interpret this condition as a lowered zone demand and decreased BTU capacity/airflow accordingly. But gradually closing the damper down as the zone comes close to satisfying complicates the airflow (static pressure) control process and makes the heat or cool demand last longer than necessary,” explains Brown.
The installations between a furnace and heat pump are quite similar but “The differences come down to wiring and programming. A heat pump installation has more wires to run and connect,” explains Brown.
This can make the installation of a thermostat in a retrofit application tricky due to the requirement to run wires in areas where there were none before. “Then people may also upgrade equipment and move from a single stage to a multi-stage, and the concern will be whether they have enough wires to control that extra stage,” explains Bauman.
Retrofit jobs will require much more creativity and planning when incorporating a zoned system. As Foster explains, “In these older homes, access to dampers may be an issue, and that’s something that may need to be changed. In these cases, mini-splits may be a solution. The mini-split system requires a contractor to bang a hole through a wall and have an inside and outside unit.”
As previously mentioned above, there is no one right solution for zoning. There are different ways to zone a home, and each home will require its own approach. One solution can be utilizing mini-splits. “You are still zoning the house when you decide to use a mini-split heat pump on a new addition because you cannot route the required duct size from your existing equipment to the new area. You will have two HVAC systems instead of one, but you have still zoned the new house addition,” explains Brown.
While the reasoning isn’t completely clear as to why every home isn’t zoned, for some contractors, it’s because they are still unfamiliar with the technology. “I’ve talked to some contractors, and when I ask them about zoning, they mention things like it’s too difficult or they aren’t comfortable doing it. The thing is, no one is forcing contractors to zone. However, we need to zone more homes. We need to make homes run more effectively and efficiently, and zoning can help with that,” said Foster.