Mini-Mini-Splits

When you think of heat pump HVAC systems, you probably picture large, permanent units - like a furnace in the attic or a mini-split system with refrigerant lines snaking around the house. At one time, computers were massive machines that took up entire rooms. Today, we do all our computing from a device that fits in our hand. Could the same shift happen with heat pumps?

Let’s explore that idea. What if heat pumps were less like big, permanent installations and more like portable devices?

Heat Pumps are Better Space Heaters

A limitation of traditional resistive electric space heaters is that a typical household circuit is 15 to 20 amps. This means the wiring, breaker, and panel restrict how much power a heater can supply. The National Electric Code restricts loads to 80% of a circuit's total capacity, which translates to about 1500 watts for space heaters. Between that and issues around fire risks and safety, space heaters are usually temporary solutions.

But the magic of a heat pump is that it lets you magnify the amount of heat you can pump with the same power input. Because they move heat rather than creating it, they can have efficiencies of 300% or more. This means that instead of 1500 watts, you can effectively pump 4500 watts of heat with a heat pump on the same household circuit. That’s a significant difference - it means you could more effectively heat (or cool) your house with a portable device that plugs into a standard outlet.

HVAC equipment is typically sized in units of BTU/hr, and a typical 1500 square foot California home may require around 36,000 BTU/hr of heating for the coldest days of winter. 1 BTU/hr corresponds to roughly 0.3 watts, which means that the demand of a typical home could be served by just 2 or 3 portable heat pump systems, plugged into a standard 15 amp wall outlet.

A heat pump in every window?

Is there a world where we could shift our expectations of what heating and cooling systems look like? Are small, easy to install heat pumps a magic bullet?

Gradient is already pushing this boundary with their window heat pump. It looks similar to a standard window AC but does both heating and cooling, using an inverter compressor to run quietly and avoid the ‘window shaker’ reputation. Its saddle design blocks less window space, a common complaint with traditional window ACs.

Other manufacturers, like Midea, have also caught on and now offer their own versions of packaged window heat pumps that sit below the window sill. The value proposition of these systems is that they can be easily installed without specialized labor.

Both the Midea and Gradient systems have gained traction through a New York City program aimed to provide clean heating for apartment buildings. In total, they’ve been contracted to supply 30,000 units for the New York City Housing Authority, and have teamed up with entities like BlocPower to install these systems.

Window units aren’t a silver bullet

Window units come with their own set of problems. There remains a stigma around window air conditioning units as “cheap” options, especially in higher-end homes. Are cost benefits alone sufficient to overcome this perception?

The cost benefits are murky, too. While a traditional window AC may cost a few hundred dollars, Gradient’s system sells for $3,800 while Midea is targeting a $3,000 price tag for their unit. At this price point, they very quickly lose any cost advantage over more traditional central or mini-split heat pump systems if more than a few units are required.

Another concern is security. Windows never fully close or latch with a window AC, so if you're on a ground floor it can leave your home vulnerable. This may be a bigger issue in lower-income communities which might benefit the most from lower cost heat pumps, but where security could be a greater concern.

There’s also the option of portable heat pump units with flexible hoses. Although these can be more affordable than saddle style window heat pumps, they’re generally less efficient due to heat loss through uninsulated hoses.

Another consideration is that portable and window heat pumps aren’t as easily controlled from a single location like a central heat pump. Most have simple controls and don't communicate with each other. However, third party IR-based thermostats like Flair, Sensibo and Mysa enable multiple units to be controlled from a single interface.

Other easier-to-install systems

Window and portable heat pump systems are options that can both be installed and removed easily. They’re one end of the spectrum, but there are also options between a “temporary” system and a traditional heat pump installation.

Packaged unitary through-the-wall heat pumps from companies like Ephoca and Olimpia Splendid are one option. Unlike window mounted systems, these require a more challenging installation process with large holes drilled into the wall for air intake and exhaust. However, they avoid the need for speciality skills like refrigerant handling and electrical work necessary in a traditional heat pump installation. They provide an interesting middle ground between portable units and full installation.

Even when looking at more standard mini-split systems, there are opportunities to simplify the installation process. In much of the world, HVAC systems just plug into a wall outlet without dedicated wiring. However, In the US, HVAC equipment generally requires a dedicated circuit. Perhaps we could make specific carve-outs in the building code to allow heat pumps to plug into normal outlets? That could drive down installation costs for some mini split systems because you wouldn’t need to pull a dedicated circuit - you could just plug it in.

Ultimately, the challenge is figuring out where on the spectrum - from no installation to full installation - we can find a solution that fits the needs of most people. It’s likely that each of these options will work together, filling the needs of a particular segment of the market.

The role of Unlicensed labor

A new bill called AB 2622 was recently signed into law in California. This little discussed ruling raised the maximum value for projects completed by unlicensed contractors from $500 to $1,000, inclusive of all parts and labor.

Professional licensing plays an important role in ensuring quality and protecting homeowners from risk and liability. Some requirements to obtain a license include years of experience in the field, holding bonds and insurance policies in good standing, attestations from prior supervisors on work experience, testing that covers both the subject matter and contracting law, and fingerprinting and background checks. Much of HVAC work today requires specialized skillsets, so the barrier to entry is a good thing.

However, there are plenty of competent handymen with good general-purpose technical skills whose expertise could be applied towards electrifying our homes. If we can keep project scope sufficiently simple and small, then this unlocks a much larger labor pool to deploy heat pumps at scale.

There are a few restrictions in AB 2622 that somewhat limit the applicability of unlicensed labor - it can’t be used for projects that require a permit, and larger projects can’t be broken down into a bunch of smaller projects completed over time to manipulate the $1,000 limit.

New business models?

The limitations around permitting and project cost prevent unlicensed technicians from doing a full, traditional HVAC install. But there are opportunities around new systems that can be installed without permits.

While the options from Gradient, Midea, Ephoca and Olimpia are too expensive to fit into the $1,000 project limits, the equipment could be supplied by the homeowner with an unlicensed handyman doing the installation. While supplying your own equipment is generally a bad idea, in this particular case it makes sense.

We might even see more models like RentAnAC, who provide rental window air conditioners with installation services in the northeast. It’s not unreasonable that a $3,800 heat pump unit could rent out for under $1,000 for a season.

Thinking inside the box

Most homeowners still prefer professionally installed central or mini-split heat pump systems for their home, and alternate types of heat pump systems remain fairly niche. However, they do offer benefits and are one tool that could help accelerate heat pump adoption in the US.

What do you think - would you consider a portable window heat pump for your home?

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