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Heat Pump Clothes Dryers: Low-Impact Laundry
CategoriesSustainable News Zero Energy Homes

Heat Pump Clothes Dryers: Low-Impact Laundry

By Zarkon Group,

If you’re interested in shaving off perhaps 10% of your household energy use (and your electric bill) with a single purchase, it’s time to look into heat pump clothes dryers. “An electric dryer can use anywhere from 700 to 1000 kilowatt-hours of electricity each year. That’s about a tenth of the average American’s electricity usage,” said Joe Wachunas, electrification advocate for Electrify Now and Project Manager at New Buildings Institute. “You can cut that by 75% or more using heat pump dryers.”

With options on the market that use as little as 200 kWh of energy in a year, it’s not hard to see why their market share is increasing. “Heat pump technology is critical here in America, especially,” Wachunas says. “And heat pump dryers are an exciting, relatively new technology.”

Traditional vented dryers

Vented dryers can be either gas or electric, and they require venting to the outside of the home through ducts. A heating element heats the air in the drum, evaporating the moisture from clothes. Then as the dryer runs, the hot, moist air is vented outside and replaced with air pulled in from your laundry room, basement, or wherever it’s located. This influx of fresh air must be heated to continue drying the clothes.

Ga-Young Park,  Residential Appliances Manager at ENERGY STAR, pointed out another inefficiency. “Because vented dryers pull in cooled or heated air from your home and vent it outdoors, your air conditioner or heater has to work even harder to maintain the indoor temperature.” Also, vented dryer drums get very hot during operation, which—aside from the fire risk—can overdry clothes and potentially damage fabrics.

Heat pump clothes dryers

Electric-powered heat pump dryers (aka ventless or condensation dryers) dry clothes without using a heating element or vent. Instead, heat pump technology pulls air into a condenser, heats it, and sends it into the drum, where it absorbs moisture from the wet clothes. Then, the air cycles to an evaporator, where it’s cooled. As the air gets colder, it loses moisture, which is either drained or collected in a removable tray.

That same air is then pulled from the evaporator into the condenser to be reheated while it’s still warm. In other words, heat pump dryers recycle warm air instead of venting it to the outdoors. Not having to heat fresh, cold air leads to big energy savings. Park added, “Heat pump models dry laundry at lower temperatures, which is much gentler on clothes. And unlike vented dryers, there’s basically no fire risk.”

Hybrid heat pump dryers

Hybrid heat pump dryers combine the heat pump cycle with the heating element of a vented dryer. This pairing helps the dryer drum get hotter, so clothes dry faster. Hybrid heat pump dryers are much more efficient than vented dryers, but because of the heating element, they’re less efficient than pure heat pump dryers.

Bosch heat pump dryer in butler's pantry setting; white tile and gray cabinets

Bosch WTG86403UC 300 Series 24 Inch Smart Electric Dryer, ventless. Images courtesy Amazon.

Size, price, and dry time

“People often think heat pump dryers take way longer to dry clothes because they use lower temperatures,” said Park. In reality, heat pump models can have dry times comparable to many vented dryers on the market today. All models with the ENERGY STAR label meet an 80 minute maximum dry time for a “typical” cycle, and some newer models demonstrate dry times as low as 50 to 35 minutes.

Historically, heat pump dryers have been compact in size, smaller than typical US household dyers. Things are changing, though. Park reported only ten options for standard-size dryers with heat pump technology, but expects that more standard-size heat pump dryers will continue to come on the market, particularly as hybrid models become more available.

Heat pump dryers are definitely more expensive than traditional vented dryers, but more and more, utility-sponsored rebates are available to offset the cost differential. Owners may also save on installation. Heat pump dryers do not require venting ductwork, which makes them simpler and less expensive to install. Homeowners can install the dryers nearly anywhere, provided the condensed water is allowed to collect or drain along with the washer.

Of course, you’ll also see major savings on your monthly energy bill.

Finally, the Inflation Reduction Act (IRA) will provide additional rebates and tax credits for homeowners looking to make energy-efficient home upgrades. (This savings calculator can help you estimate how much money you can save on a heat pump dryer through the IRA.)

Note: European households use an average of 3,700 kWh of electricity each year, just a third of what Americans use. Not coincidentally, while most of the world saves big money and energy by hanging clothes outside to dry, the practice is restricted or completely banned by many communities across the United States!

ENERGY STAR’s 5 Most Efficient Dryers

ENERGY STAR, run by the US Environmental Protection Agency, has overseen testing and labeling of quality, energy-efficient products for more than 30 years. The blue ENERGY STAR label signifies brands and models that are leaders in energy efficiency.

ENERGY STAR ranks dryers based on their Combined Energy Factor (CEF), a measure of energy efficiency. The higher a dryer’s CEF, the more energy efficient it is.

ENERGY STAR’s five most energy-efficient clothes dryers (unpaired units) are all heat pump dryers (as of January 1, 2024).

Blomberg – DHP24404W 

  • Combined Energy Factor (CEF): 11.0
  • Estimated Annual Energy Use: 217 kWh/yr
  • Estimated Energy Test Cycle Time: 67 minutes
  • Additional Features: Sanitization cycle, Filter cleaning indicator, Steam cycle, Drum light, Time remaining display

Beko – HPD24414W 

  • Combined Energy Factor (CEF): 11.0
  • Estimated Annual Energy Use: 217 kWh/yr
  • Estimated Energy Test Cycle Time: 67 minutes
  • Additional Features: Sanitization cycle, Filter cleaning indicator, Steam cycle, Drum light, Time remaining display

Miele – PDR908 HP

  • Combined Energy Factor (CEF): 9.75
  • Estimated Annual Energy Use: 245 kWh/yr
  • Estimated Energy Test Cycle Time: 53 minutes
  • Additional features: Filter cleaning indicator, Drum light, Wrinkle prevention option, Time remaining display

Asko – T411HS.W.U

  • Combined Energy Factor (CEF): 9.1
  • Estimated Annual Energy Use: 263 kWh/yr
  • Estimated Energy Test Cycle Time: 80 minutes
  • Additional features: Filter cleaning indicator, Drum light, Wrinkle prevention option, Time remaining display

LG – DLHC5502*

  • Combined Energy Factor (CEF): 9.0
  • Estimated Annual Energy Use: 266 kWh/yr
  • Estimated Energy Test Cycle Time: 68 minutes
  • Additional features: Wrinkle prevention option, time remaining display, drum capacity 7.8 cu-ft

This article springs from Electrify Now’s webinar on Heat Pump Dryers. Their followup, Heat Pump Dryers – Update on Brands and Options, compares units from Bosch, Miele, GE, and LG:

The author:

Catherine Poslusny is a freelance writer and content marketing specialist based out of Norman, OK. You can find her at catherinerosewrites.com.

Reference

We Are the Rare, Repeat Heat Pump Water Heater Customers
CategoriesSustainable News Zero Energy Homes

We Are the Rare, Repeat Heat Pump Water Heater Customers

By Zarkon Group,

The word is now out, and sales of heat pump water heaters (HPWHs) are taking off. New rebates, mandates, and tax credits will likely drive sales through the roof by the end of this decade. Heat pump water heaters use a fraction of the energy of legacy technologies, with great performance, which means lower utility bills along with reduced carbon emissions. We’ve embraced the technology on our journey to electrify two different properties, and we were among the first in the US to buy and install a 120V plug-in heat pump water heater at our family home in Ohio.

Why do we sing their praises?

Cost!

The heat pump water heater is among the most affordable climate-saving technologies available. While solar panels and electric cars are vital tools for climate warriors, a heat pump water heater saves the energy equivalent of seven solar panels while costing only one-sixth the price. They run approximately $1600 for the appliance, plus $1000 to $3000 for installation, depending on the fuel your current water heater uses. This cost is higher than traditional gas or electric-resistance water heaters, but many utilities offer rebates to bring down the price. And then add the 30% tax credit from the Inflation Reduction Act, if the property is your primary residence.

If your current water heater is gas, you may need to run a 240V electrical line, unless you get a new 120V plug-in model (for more info on this option, read about our fourth install below). If your current water heater is electric-resistance, it should already have a 240V line running to it, likely allowing a simple swap.

Efficiency

Hot water accounts for a substantial share of energy use in buildings—17% in single family homes and up to 32% in multi-family—hundreds of dollars a year. Heat pumps move heat rather than create it. So heat pump water heaters are three to five times more efficient than standard water heaters. They look just like a legacy water heater, but a bit taller because the heat pump sits on top of the water tank.

They cost very little to operate: $100 to $150 a year for a family of four, saving $550 compared to an electric resistance water heater and $200 less than a gas water heater. A new heat pump water heater can pay for its higher upfront cost in just a few years. And then it’s saving you money each year after that.

Graphical image depicting carbon savings of heat pump water heater; text reads "A heat pump water heater saves 1 ton of CO2 per year. That's like planting 17 trees"; imagery includes trees and water heater plus logo of Advanced Water Heating Initiative

Source: Advanced Water Heating Initiative.

Carbon

Sure heat pump water heaters are super energy efficient, but they also run on electricity, which means they can use renewable electricity. Replacing a single gas water heater with a heat pump unit will save around 1 ton of CO2 annually.

And the word is out. While heat pump water heaters currently account for only less than 2% of new water heater sales, they jumped 26% in 2022 as sales of natural gas water heaters fell. Heat pump water heaters could increase to half of all water heater sales by 2030.

Propelling electrification

Electricity is the only widely-available, scalable fuel option that is quickly decarbonizing. So reducing climate change involves converting everything to highly efficient, clean electricity. A common critique of the electrification movement is that the electrical grid can’t handle the additional loads to replace fossil fuels used in buildings and transportation. Enter heat pumps. Widespread deployment of heat pumps in HVAC and hot water production will save tremendous energy: enough to power new electrical loads, like electric cars (EVs), on the existing grid.

Graphic showing electricity required for home EV charging can be net-zero due to energy saved by installing heat pump water heater

Heat pump water heaters (HPWH) will likely save nearly all the electricity a household needs to operate an EV.

As Americans transition to EVs over the next decade, heat pump water heaters alone will likely save nearly all the electricity that a household needs to operate an EV. This statistic shows how much energy we currently waste in heating our water. And this EV electrical load is replacing carbon-intensive gasoline and diesel fuels.

About half of the US currently has electric resistance water heaters, so as those homes switch to heat pump water heaters, we won’t have to worry about finding more electricity for EVs. Their utility bills will likely stay constant, saving them all the money they currently spend at the gas pump.

The other half of homes heats water with fossil fuels, so we will need to find added clean electricity for those water heaters and vehicles. (But transitioning electric-resistance space heaters and clothes dryers to heat pump units produces savings similar to switching out water heaters.) Most heat pump water heaters run on 240V (the same as conventional electric water heaters and dryers), but if your old water heater runs on gas, you may have to install a new power line from the panel. But a 120V plug-in model is the newest option. If your current water heater is electric, it will likely be an easy swap: no need for an electrical panel upgrade or service upsize from the utility.

heat pump water heater installed in residential closet surrounded by various tools and clothing items - photo

2017: HPWH replacing an aging water heater

Our old gas water heater was nearing its end of life, and Joe was excited about the technological advance of heat pumps for water heating. Though we still had questions about installation and performance.

It’s easiest to install a heat pump water heater in a basement or garage, because they exhaust cool air. But our heat pump water heater resides in a coat closet in the middle of our living space, venting into the attic. There it draws the warmest air in our house and exhausts to an unconditioned space. (Note that there are lots of options for locating heat pump water heaters in living spaces without ducting.)

Of course there were no local installers familiar with heat pumps back then, but after watching YouTube, Joe felt OK working with a trusted handyman. Even though it was a gas conversion, an existing 240V electrical line made things much easier. Ever since, this unit has consistently provided our family plus an Airbnb with plentiful hot water.

2019: HPWH replacing a functioning gas hot water heater

We did not get the full life out of the existing gas hot water heater in the accessory dwelling unit on our property. We chose to replace a perfectly good appliance (only 7 years old) with a heat pump water heater powered by clean solar energy. Our goal was to eliminate fossil fuels from our home. We used the same attic-ducting technique as the water heater in the main house, locating the unit in a closet. This mighty unit provides plenty of hot water for the tenant and runs the radiant floor heating system as well. (We don’t recommend heat pump water heaters for floor heating, as it is not a proven or scalable application.)

2020: HPWH replacing a decrepit gas water heater

During COVID, we undertook an interiors and sustainability renovation of a duplex in Cleveland, OH, that has been in our family for 75 years. In transitioning to all-electric, we replaced an almost 30-year-old basement water heater with our favorite heat pump. In addition to reducing our energy bill by $200 a year, it provides great dehumidification: about 2–4 quarts of water per day. If you currently run one or more dehumidifiers in your damp, Midwestern basement, you may save hundreds more.

The plumber added a new 240V power line, and ran the condensate tube to the floor drain. The basement maintains about 60 °F all winter, and we’ve never needed to engage the less-efficient backup electric-resistance heating elements.

Plumber works to install 120 V heat pump water heater - photo

2023: The new 120V heat pump water heater

This past summer, we replaced the other 30-year-old gas water heater in the basement of the Cleveland duplex. This just-arrived-on-the-market 120V unit eliminated the need to run 240V power from the panel. As heat pump enthusiasts, we were excited to test the latest tech. Perhaps the most difficult step was placing the custom order with Home Depot. Though now it’s readily available!

The installation was the easiest part. It took the plumber (who had never heard of a heat pump water heater) only 2.5 hours to complete the job, about the same as a standard gas water heater. The 120V heat pump water heater plugs right into a standard outlet. But he did have to run the condensate tube into the floor drain nearby and cap the gas line.

The 120V unit has been humming along for months—it’s very quiet—using a mere 65 kWh in the first month of operation. We monitor its performance through the manufacturer’s app, so we know it remains ridiculously efficient and almost always completely full of hot water. At a total of $3,258 installed and estimated savings of $208 a year. The 120V  models usually eliminate the backup electric-resistance heating elements by using a larger tank with more hot water stored, or by storing water at higher temperatures and then mixing in cold water to avoid scalding. Our 120V unit uses the latter strategy; see it in action.

If this were our primary residence, we might have taken advantage of the 30% tax credits for heat pump water heaters, lowering our cost to $2,281. That comes so close to the $2,000 average installed cost of a standard gas or electric water heater. And you’re still saving hundreds of dollars a year on energy costs. This proves that almost any of the 60 million US homes with a gas water heaters can easily and cheaply move towards a cleaner, decarbonized home that is less expensive to operate.

We’re big fans of making a long-term decarbonization plan, so you’re not rushing to replace broken equipment and being forced to install new circuit breakers or even a new panel or expensive electrical service upgrade. So before checking the cost of a heat pump water heater, understand your home’s installation requirements and identify a contractor or two. Then when the time, and rebates and tax credits, are right, you’re ready to switch. Because they save so much on utility bills, proactively replacing a functioning, but inefficient, water heater with a heat pump water heater may make sense—for the sake of our changing climate.

Decarbonize your life logo

This article springs from several posts by Naomi Cole and Joe Wachunas, first published in CleanTechnica. Their “Decarbonize Your Life” series shares their experience, lessons learned, and recommendations for how to reduce household emissions.

The authors:

Joe Wachunas and Naomi Cole both work professionally to address climate change—Naomi in urban sustainability and energy efficiency and Joe in the electrification of buildings and transportation. A passion for debarbonization, and their commitment to walk the walk, has led them to ductless heat pumps, heat pump water heaters, induction cooking, solar in multiple forms, hang-drying laundry (including cloth diapers), no cars to electric cars and charging without a garage or driveway, a reforestation grant from the US Department of Agriculture, and more. They live in Portland, OR, with two young children.

 

Reference

Heat Pump Dryers: Low-Impact Laundry
CategoriesSustainable News Zero Energy Homes

Heat Pump Dryers: Low-Impact Laundry

By Zarkon Group,

If you’re interested in shaving off perhaps 10% of your household energy use (and your electric bill) with a single purchase, it’s time to look into heat pump dryers. “An electric dryer can use anywhere from 700 to 1000 kilowatt-hours of electricity each year. That’s about a tenth of the average American’s electricity usage,” said Joe Wachunas, electrification advocate for Electrify Now and Project Manager at New Buildings Institute. “You can cut that by 75% or more using heat pump dryers.”

With options on the market that use as little as 200 kWh of energy in a year, it’s not hard to see why their market share is increasing. “Heat pump technology is critical here in America, especially,” Wachunas says. “And heat pump dryers are an exciting, relatively new technology.”

Traditional vented dryers

Vented dryers can be either gas or electric, and they require venting to the outside of the home through ducts. A heating element heats the air in the drum, evaporating the moisture from clothes. Then as the dryer runs, the hot, moist air is vented outside and replaced with air pulled in from your laundry room, basement, or wherever it’s located. This influx of fresh air must be heated to continue drying the clothes.

Ga-Young Park,  Residential Appliances Manager at ENERGY STAR, pointed out another inefficiency. “Because vented dryers pull in cooled or heated air from your home and vent it outdoors, your air conditioner or heater has to work even harder to maintain the indoor temperature.” Also, vented dryer drums get very hot during operation, which—aside from the fire risk—can overdry clothes and potentially damage fabrics.

Heat pump dryers

Electric-powered heat pump dryers (aka ventless or condensation dryers) dry clothes without using a heating element or vent. Instead, heat pump technology pulls air into a condenser, heats it, and sends it into the drum, where it absorbs moisture from the wet clothes. Then, the air cycles to an evaporator, where it’s cooled. As the air gets colder, it loses moisture, which is either drained or collected in a removable tray.

That same air is then pulled from the evaporator into the condenser to be reheated while it’s still warm. In other words, heat pump dryers recycle warm air instead of venting it to the outdoors. Not having to heat fresh, cold air leads to big energy savings. Park added, “Heat pump models dry laundry at lower temperatures, which is much gentler on clothes. And unlike vented dryers, there’s basically no fire risk.”

Hybrid heat pump dryers

Hybrid heat pump dryers combine the heat pump cycle with the heating element of a vented dryer. This pairing helps the dryer drum get hotter, so clothes dry faster. Hybrid heat pump dryers are much more efficient than vented dryers, but because of the heating element, they’re less efficient than pure heat pump dryers.

Bosch heat pump dryer in butler's pantry setting; white tile and gray cabinets

Bosch WTG86403UC 300 Series 24 Inch Smart Electric Dryer, ventless. Images courtesy Amazon.

Size, price, and dry time

“People often think heat pump dryers take way longer to dry clothes because they use lower temperatures,” said Park. In reality, heat pump models can have dry times comparable to many vented dryers on the market today. All models with the ENERGY STAR label meet an 80 minute maximum dry time for a “typical” cycle, and some newer models demonstrate dry times as low as 50 to 35 minutes.

Historically, heat pump dryers have been compact in size, smaller than typical US household dyers. Things are changing, though. Park reported only ten options for standard-size dryers with heat pump technology, but expects that more standard-size heat pump dryers will continue to come on the market, particularly as hybrid models become more available.

Heat pump dryers are definitely more expensive than traditional vented dryers, but more and more, utility-sponsored rebates are available to offset the cost differential. Owners may also save on installation. Heat pump dryers do not require venting ductwork, which makes them simpler and less expensive to install. Homeowners can install the dryers nearly anywhere, provided the condensed water is allowed to collect or drain along with the washer.

Of course, you’ll also see major savings on your monthly energy bill.

Finally, the Inflation Reduction Act (IRA) will provide additional rebates and tax credits for homeowners looking to make energy-efficient home upgrades. (This savings calculator can help you estimate how much money you can save on a heat pump dryer through the IRA.)

Note: European households use an average of 3,700 kWh of electricity each year, just a third of what Americans use. Not coincidentally, while most of the world saves big money and energy by hanging clothes outside to dry, the practice is restricted or completely banned by many communities across the United States!

ENERGY STAR’s 6 Most Efficient Dryers

ENERGY STAR, run by the US Environmental Protection Agency, has overseen testing and labeling of quality, energy-efficient products for more than 30 years. The blue ENERGY STAR label signifies brands and models that are leaders in energy efficiency.

ENERGY STAR ranks dryers based on their Combined Energy Factor (CEF), a measure of energy efficiency. The higher a dryer’s CEF, the more energy efficient it is.

ENERGY STAR’s six most energy-efficient clothes dryers are all heat pump dryers (as of January 1, 2023).

Blomberg – DHP24404W 

  • Combined Energy Factor (CEF): 11.0
  • Estimated Annual Energy Use: 217 kWh/yr
  • Estimated Energy Test Cycle Time: 67 minutes
  • Additional Features: Sanitization cycle, Filter cleaning indicator, Steam cycle, Drum light, Time remaining display

Beko – HPD24414W 

  • Combined Energy Factor (CEF): 11.0
  • Estimated Annual Energy Use: 217 kWh/yr
  • Estimated Energy Test Cycle Time: 67 minutes
  • Additional Features: Sanitization cycle, Filter cleaning indicator, Steam cycle, Drum light, Time remaining display

Miele – PDR908 HP

  • Combined Energy Factor (CEF): 9.75
  • Estimated Annual Energy Use: 245 kWh/yr
  • Estimated Energy Test Cycle Time: 53 minutes
  • Additional features: Filter cleaning indicator, Drum light, Wrinkle prevention option, Time remaining display

Asko – T411HS.W.U

  • Combined Energy Factor (CEF): 9.1
  • Estimated Annual Energy Use: 263 kWh/yr
  • Estimated Energy Test Cycle Time: 80 minutes
  • Additional features: Filter cleaning indicator, Drum light, Wrinkle prevention option, Time remaining display

Samsung – DV53BB89**H*

  • Combined Energy Factor (CEF): 8.5
  • Estimated Annual Energy Use: 281 kWh/yr
  • Estimated Energy Test Cycle Time: 69 minutes
  • Additional features: Sanitation cyle, drum capacity 7.8 cu-ft

LG – WKHC202H*A 

  • Combined Energy Factor (CEF): 8.0
  • Estimated Annual Energy Use: 299 kWh/yr
  • Estimated Energy Test Cycle Time: 72 minutes
  • Additional features: Wrinkle prevention option, time remaining display, drum capacity 7.2 cu-ft

This article springs from Electrify Now’s webinar on Heat Pump Dryers. For more strategies and technologies to electrify your home, visit their YouTube Channel.

By Catherine Polslusny

Reference

What Is a Mini-Split Heat Pump?
CategoriesSustainable News Zero Energy Homes

What Is a Mini-Split Heat Pump?

By Zarkon Group,

By Allison A. Bailes III, PhD

Ah, mini-splits. They’re all the rage in the world of high-performance HVAC. But what exactly is a mini-split heat pump? Unfortunately, the terminology around this technology is confusing because it’s used so inconsistently. Let’s start at the beginning.  Well, OK, not all the way at the beginning.  I’m not going to explain what a heat pump is, but here’s a primer on how they work for heating.

The Basic Meaning of Mini-Split

The term “mini-split” originally referred to a split system heat pump, used for heating or cooling or both, with a smaller capacity than conventional systems. In that sense, a mini-split is just what its name says:  a small split system heat pump.  It gets confusing in the different ways manufacturers make these lower-capacity, split-system heat pumps.

A mini-split, for example, can have a conventional fixed-capacity compressor or an inverter-driven variable-capacity compressor. So, a mini-split could be a conventional heat pump that’s just smaller. Or, it could be a smaller heat pump with variable capacity. The former type is rare, though, so when you hear the term “mini-split,” you should think of the type with the inverter-driven compressor with variable capacity.

But it gets worse.  This heating and cooling system has outgrown its name…at least the “mini” part.  Yes, you can still get them down to a half-ton of capacity (6,000 BTU per hour), with smaller capacities on the way.  But you can also get mini-splits that have a capacity of 4 tons (48,000 BTU per hour), which is far from “mini.”

Is It a Mini-Split…or a Multi-Split?

Another confusing area is that with this type of heat pump, the outdoor unit can be connected to one indoor unit (referred to as one-to-one), or it could be connected to multiple indoor units. Some people distinguish these two types by using the term “mini-split” only for the one-to-one configuration.  They say that when you have more than one indoor unit on a single outdoor unit, that’s a multi-split heat pump.

The wall-mounted ductless mini-split heat pump in my sunroom. This is the only indoor unit connected to the outdoor unit, making it a one-to-one setup.

If we go with that dividing line, I have both a mini-split and a multi-split in my house.  The central part of the house is heated and cooled with one outdoor unit connected to two indoor ducted air handlers.  That would make it a multi-split.  I use a one-to-one ductless system for my sunroom (above).

Are All Mini-Splits Ductless?

And then there’s the issue of the type of indoor unit. Some are ductless, and they come in different flavors: wall-mounted, ceiling cassettes, and floor-mounted. Others are ducted, and they come in horizontal ducted or multi-position types. Some people use the term “mini-split” only for indoor ductless units. Others refer to any split system with smaller capacity as a mini-split, whether the indoor unit is ducted or ductless.

One of the ducted air handlers for the mini-split heat pump being installed in my house in 2019

I use the term “mini-split” for all of the above. Since mini-splits with fixed-capacity compressors are rare, you don’t need to worry about that confusion. If you’re talking to someone about mini-splits, you should be able to tell from the context how they use the term. If not, ask them to clarify.

Inverter-Driven Mini-Split Heat Pumps

Inverter-driven mini-split heat pumps are the future for high-performance homes. I’ve got them in my home, and it’s what we specify in most of our HVAC design jobs at Energy Vanguard. Their high efficiency and variable capacity that can ramp down to very low values are perfect for superinsulated, airtight homes, such as zero energy homes or passive homes.  And they work well in less efficient homes, too.

They give you a couple of other benefits. Their lower capacity means you can zone your heating and cooling with separate pieces of equipment. And using separate pieces of equipment provides resilience. If one heat pump stops working, you can still heat or cool the parts of the house that have operable equipment.

One final point here concerns the one-to-one configuration. If you want the highest efficiency, the best zone-to-zone control, and the most resilience, use only one indoor unit on each outdoor unit. Multi-split systems can work fine, but they’re just not as good as one-to-one setups.

Can You Oversize Heat Pumps?

One of the great advantages of using mini-splits is their variable capacity, but by oversizing them, you can lose that advantage completely.  That 6,000 BTU per hour mini-split in a room with 1,500 BTU per hour of cooling load doesn’t act at all like it has variable capacity because it’s always running at the lowest capacity.

So, yes, you absolutely can oversize a mini-split.  And when you do, you end up with some of the same problems from oversizing conventional systems:  poor humidity control, short cycling, and wasted money.

When a contractor proposes seven indoor ductless units for a 2,100 square foot house without a load calculation, there’s close to a 100% chance that the systems will be oversized.  And this problem happens with new homes that get load calculations, too, unless the load calculations are done correctly. You’ve got to look at the specifications for any mini-split heat pump in conjunction with the heating and cooling loads of the home and put in one that will take full advantage of the variable capacity.

Heat Pumps Are the Future of HVAC

Whether you live in frigid  Minnesota or hot and humid Georgia, as I do, going with a heat pump is a great idea, especially if you’re replacing a gas heating system.  Unlike fossil gas, electricity is getting cleaner, and mini-split heat pumps are the most efficient way to use clean energy for heating and cooling.

Allison A. Bailes III, Ph.D., is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and writes the Energy Vanguard Blog. He is also writing a book on building science. You can follow him on Twitter at @EnergyVanguard.



Reference