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Many contractors are accustomed to installing heat pumps in warmer areas, where they've been widely used for a long time. However, with the emergence of cold climate heat pumps, demand is shifting to cooler areas, requiring contractors to size systems more carefully in order to avoid mold problems and homeowner discomfort

COLD CLIMATES: At a recent conference, ACCA’s Ed Janowiak explained how to properly size heat pumps for cold climates. (Staff photo)

Humidity Control

Janowiak pointed out that one common misconception is that with inverter systems, contractors can install any size heat pump and expect optimal cooling performance, even in humid climates. However, this is incorrect, he said, as oversizing heat pumps for cooling needs can result in inefficient operation and poor humidity control, leading to mold issues and occupant discomfort.

“I want to say right from the start that I like heat pumps. I live in a heating climate, and I have two heat pumps in my house,” said Janowiak. “But I keep hearing people say you can put in one of these inverter systems and size it however you want, and the cooling will be fine. If you live in 80% of the country that has green grass or humidity, it's not necessarily going to work properly.”

To tackle this issue effectively, contractors need to adhere to industry standards such as ACCA’s Manual S, which often gets overlooked compared to Manual J and Manual D, said Janowiak. Manual S outlines how to size heat pumps in heating climates based on cooling requirements, with supplementary heat as a backup option. This ensures efficient operation and addresses the need for humidity control.

“Heat pumps should be sized to the cooling requirement, and in some areas, it may even be a code requirement,” said Janowiak. “In colder climates, use supplementary heat to make up for Btu below the thermal balance point. That is my favorite path. I like supplementary heat. Electric resistance reheat can also be used to remove humidity.”

Manual S also explains important concepts such as sensible heat ratio (SHR), which is the ratio of sensible load to total cooling load from the Manual J load calculation, as well as sensible heat factor (SHF), which is the ratio of the equipment’s sensible cooling capacity to total cooling capacity at a given set of operating conditions. Essentially, SHF represents the sensible heat ratio of equipment, while the SHR represents the sensible heat ratio of the structure, said Janowiak. Both concepts are important to understand when designing a heat pump system that will optimize moisture removal without sacrificing cooling efficiency.

Equipment Selection

Multi-stage heat pumps may also be able to take care of the entire heating load and still control humidity, said Janowiak; however, the bigger the discrepancy between the gain and loss, the less likely this is going to happen.

“This may work, but there are folks out there who are trying to convince people that may will be replaced with will, so don't fall into that trap,” he said. “If you're curious about any of these pieces of equipment and what they'll do, look them up. The people who are saying to put in these giant heat pumps and that they'll take care of the air conditioning load obviously have not looked it up. Because if they looked it up, they'd realize what they're encouraging you to do doesn't work.”

Another equipment configuration that contractors should consider is a dual fuel system, which typically combines a heat pump with a gas furnace. That makes a lot of sense to Janowiak, who noted, “In my mind, the best two-stage system is a dual fuel. With a two-stage furnace, it runs at two-thirds to three-quarters of its capacity on low fire. But if you put in a heat pump and a furnace, that heat pump's capacity is probably half of the first stage of the furnace. Less Btu, more runtime, more better. Follow that pattern. It's always going to be your friend.”

In the end, when it comes to selecting a heat pump for a heating climate, Janowiak said that the choice is simple: accept that supplementary heat is required, or design the system with ancillary dehumidification in mind. The latter option will likely not be attractive to consumers, he said, as it will substantially increase the price of the system.

“There are two paths. You're either going to make the house humid and cold, or it's going to be warmer than desired for part of the year. Pick one,” he said. “If you size the system right — using the indoor design conditions of 75°F and 50% relative humidity per Manual J — then some part of the year, the homeowners are going to be hotter than they want it to be, but that system isn't going to cause damage to that house. If you go off square footage and oversize the system by a ton, then you’ll have a damp, uncomfortable, unhealthy home for the occupant and the structure itself.”

That is why contractors should resist the urge to oversize heat pump systems, particularly in heating climates. “When did it become okay to oversize an air conditioner? If you said never, you were correct, because it never was acceptable. We've gone through this before — the bigger isn’t better thing — over and over and over … There's no free lunch. Either you're going to put in something that properly dehumidifies the space, or you're not.”

Contractors who ignore that advice do so at their own peril, as this could lead to heat pumps getting a bad name again — similar to what happened several decades ago. This could undermine current efforts towards electrification, which are fueled by substantial financial incentives.

“Sizing to heating requirements could start the great heat pump revolt of 2027,” said Janowiak. “If we keep on the path that we're on right now, we're going to have a lot of pissed-off people. And you know what? They should be pissed off. People who are offering the big refunds and incentives are encouraging contractors to do things in a way that they know isn’t right. But if ‘we’ put in the effort, we can point this in a direction where all involved can meet their goals.”