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If you've found a heat pump that's the right size for your house, with the right performance for your local climate, you're in great shape, especially with an inverter heat pump.
Beyond those fundamental specs, the best way to make yourself more comfortable and save energy is to make sure your home meets some common-sense standards for insulation and air sealing. If you're using a ducted heat pump, you need decent ductwork, too. Seriously, take care of this stuff! These steps can slash your energy use by 30 percent or more in some cases, enough to cover the cost of the work through utility savings in just a couple of years.
It's also crucial to work with an installer who knows what they&#;re doing. Even if you're sure that you have a good system design, the attention to detail and craftsmanship that goes into the actual hands-on installation is also very important.
A handful of other specs can affect performance.
Turndown ratio / Minimum speed
In most parts of the US, you'll have no trouble finding at least a handful of heat pumps that'll meet your home's needs on the coldest or hottest days of the year. It's the performance on milder days that can make some heat pumps stand out.
The secret to the best performance here is having a low minimum capacity, relative to the maximum output. Sometimes this spec is called the turndown ratio. The wider the gap between the lowest and highest capacities, the more leeway the system has to work well across the widest range of temperatures. Remember, inverter heat pumps want to run as often as possible at the lowest, steadiest setting they can manage. This is how they hold steady temperatures, and it helps them eke out better efficiency. No heat pump will run 100 percent of the time, but the closer you get, the better.
A turndown ratio of 4 to 1 (the minimum capacity is 25% of the maximum) is pretty common and should work well for most systems in most homes. Some popular models only have a turndown of roughly 3 to 1 (33-35% of the capacity). That extra turndown is especially helpful in two situations.
Cold climates: The biggest beneficiaries are people who live in cold parts of the country (climate zones 5 and up), where there's a huge potential swing in temps throughout the winter and where the heating load tends to be much higher than the cooling load.
I'll use a real house and some real heating loads as an example: A pretty-good Manual J assessment done in CoolCalc (free load calculation software) says that a single-family bungalow near Boston needs 36,700 BTU of heat, at the local design temperature of 6 degrees F. At 40 degrees F (closer to the average temperature throughout the cold season) the heating load is only 17,500 BTU. And at 55 degrees F, it&#;s only 9,000 BTU.
So a 36,000 BTU cold-climate heat pump with a 4:1 turndown ratio (minimum speed 9,000 BTU, or 25% of the rated load) is pretty close to perfect for that house. It could run steadily and efficiently for almost the entire heating season. It'd likely still cycle on and off a bit during the mildest parts of the heating season (high 50s / low 60s outdoors). Would you notice any difference in comfort? Probably not with such fair weather. You could chase a wider turndown ratio, but it'd be a small payoff.
Multi-zone mini-splits: The other case where turndown ratio can make a big difference is with multi-zone systems&#;multiple indoor air handlers attached to a single outdoor unit. This is usually the most practical way to set up an entire house with ductless mini-splits, for example. But it poses a unique design challenge directly related to turndown ratios.
"A big turndown is incredibly important for mini-splits," says Peter Freedman, an HVAC designer from Massachusetts who has worked with these systems since the mid-s. A wider turndown range can help offset (or cover up) some of the compromises and shortcuts that almost always happen in a multi-zone mini-split design.
An ideal multi-zone system is one where the outdoor unit is the right size for the load of the entire building, and then each individual indoor unit is the right size for its room, and the total capacity across the indoor and outdoor units aligns perfectly. In the real world, that's hard to pull off because indoor units only come in so many sizes.
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A little bit of oversizing is usually inevitable in most rooms, and it can sometimes mean that the outdoor unit ends up being a little bit oversized as well. On a room-by-room basis, it's not such a big deal. But across multiple zones, the combined effect of that oversizing can add up, as Freedman described it to us.
The system's minimum and maximum capacity are dictated by the outdoor unit. So if all the indoor units combined ask for less heating or cooling than the outdoor unit's minimum setting, the outdoor unit will force extra capacity through the indoor heads anyway, which leads to shorter cycles&#;and shorter cycles make your home feel less comfortable while using more energy. A wider turndown ratio can smooth over these awkward compromises, in a wider range of conditions.
Turndown isn't the only important spec, and you should weigh it against other factors. The actual efficiency (best measured by the coefficient of performance, aka COP) matters more than the general rule of thumb that low turndown equals energy savings. Some models with big turndown ratios aren't especially efficient at their low settings, it turns out. Better reliability could also be worth more than a higher turndown ratio, though that's tough to gauge, as we'll cover shortly.
Dehumidification
The conventional wisdom is that inverter heat pumps are excellent for dehumidification because they run constantly, even when it's not super hot outside. As long as they're turned on, they usually pull some moisture out of the air (as long as your home isn't too dry already).
The truth is a little more nuanced than that, and it has to do with the speed of dehumidification. With a typical single-stage heat pump or central AC unit, about 25% of the energy used in a cooling cycle goes toward dehumidifying the air (known in the industry as latent heat), and the other 75% goes toward cooling the air (sensible heat). That's plenty of dehumidification even for a humid climate. After about 15 minutes, it'll bring the humidity down to a comfortable level. The downside is that once the system shuts off, the humidity will often rise faster than the air temperatures, so you're left feeling a little clammy in between cooling cycles.
Some inverter heat pumps remove moisture much more slowly, with only 10% or 5% or in extreme cases only 1% of the total energy working toward dehumidification. This happens because the indoor coil in an inverter model usually doesn't get as cold as the coil in a single-speed model&#;so when the fan blows air across the coil to cool it off, the humidity in the air doesn't condense into water as readily. It's the same reason why a cold can of soda "sweats" on a hot day, while a can at room temperature does not.
You probably don't need to worry about this, though. As long as the heat pump is the right size for your house, most models will knock the humidity down to a comfortable level during the summer. Once it gets going, it's actually better at keeping the humidity under control better than a traditional heat pump or AC. And the warm coil saves a bunch of energy, too.
During the spring and fall, when it can be humid but not very hot, all kinds of heat pumps (and ACs) can struggle to keep humidity under control.
One potential workaround: Look for a heat pump with a Dry mode, which dehumidifies the air without dropping the room temps. Plenty of mini-splits have one. If you live somewhere with a relatively short humid-but-not-hot season, this can come in handy.
Or you could look into a separate dehumidifier. That could be as simple as a portable dehumidifier (preferably with the Energy Star badge and a pump so that you don't need to remember to empty the water bucket). Or it could be a whole-house dehumidifier of some kind.
What about SEER and HSPF for efficiency?
These are the industry-standard specs that measure a heat pump's energy efficiency. SEER is for cooling, and HSPF is for heating. (The industry actually switched to SEER2 and HSPF2 as of , which are purported to reflect real-world conditions better&#;we're using the terms interchangeably here.)
Higher SEER and HSPF ratings generally lead to lower energy costs, but most industry insiders we've talked to think that they're not an accurate rating scheme for inverter heat pumps, particularly cold-climate heat pumps. The testing methodology was developed decades ago for single-speed equipment and hasn't changed enough to capture the efficiency of efficient inverter-driven models.
It's probably not worth getting too caught up in minor differences in SEER and HSPF. All inverter heat pumps are very efficient compared to whatever HVAC system you're replacing, says Edward Louie, a Building Energy Efficiency Research Engineer at the Department of Energy's Pacific Northwest National Laboratory. "It's like asking, 'Should I buy the old Prius that gets 45 miles to the gallon, or the new Prius that gets 53 miles to the gallon?' That's a measurable difference. But if your current vehicle gets 10 miles to the gallon, then it doesn't matter what you choose, it's going to be way better."
What about reliability?
A heat pump is usually a five-figure investment and protects your family and home from extreme weather, so of course you'd want one that's reliable. Unfortunately, there's not a ton of great data out there on what the most reliable heat pump brands actually are.
Consumer Reports has the best reliability info (paywalled), based on an extensive and long-running annual survey of their subscribers. It's highly trustworthy, and there's info about some major manufacturers of inverter heat pumps. But the data is incomplete. Several major brands are excluded from the rankings, and (as I learned during a stint working there) the share of data collected from people who live in cold-weather states was statistically insignificant up through .
So what can you do? You could listen to your contractor. Pros avoid working with equipment prone to repairs (at least early in the equipment's lifespan) because they're on the hook for the work under warranty. That said, they're still making decisions based on their personal experiences, which in the grand scheme of things is still a pretty limited view.
You could also look at the manufacturer's warranties as a sign of how much the installer stands behind their product. Most brands cover most parts for at least 7 years, but others extend the coverage out to 10 or even 12 years, and some will cover the cost of labor on certain parts.
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