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Now, there are lots of good reasons to consider a mini split in your home… zoned control, easy installation, high efficiencies, spot heating and cooling in an addition and so on, but one of the most important reasons to install a mini split is often overlooked…
But before we say what that is, let’s define a mini split:
Fujitsu General describes a mini split this way: “Mini-splits are heating and cooling systems that allow you to control the temperatures in individual rooms or spaces. Mini-split systems have two main components — an outdoor compressor/condenser and an indoor air-handling unit(s) (evaporator).”
Unfortunately, that definition could apply to almost any conventional system too. After a solid search of the interweb, I found that Fujitsu isn’t the only one to have difficulty defining the genre. So, here is my attempt:
“A mini split is a split system using modulating or variable speed technology that is designed to heat and cool smaller spaces and can be zoned to condition multiple smaller spaces too.” Still a bit unsatisfying, but like a lot of things, you will know it when you see it!
When thinking of mini splits, many think of ductless units (which was not in my definition, on purpose). And while many mini split units are indeed ductless, that is no longer exclusively the case. All told, mini split options include: wall mounted, floor mounted, ceiling (or cassette) mounted, mini-ducted (or pancake) units, and conventional air handlers.
Here’s an example from an Airbnb I recently stayed it This system had two indoor wall-mounted heads and one outdoor unit. It did a great job.
So… while many people know that mini splits can be incredibly efficient with very high SEER ratings, what they don’t often look at is how well mini splits do in heating mode – even with very cold outdoor temperatures. Many mini splits boast very high HSPF (Heating Seasonal Performance Factor) ratings, which is a number that tries to capture how efficient the system is at taking one form of energy (electricity) and converting it to another form of energy (heat), with the higher the number the better. In fact, many mini split heat pumps boast ratings of 10.0 or higher! (In contrast, most conventional heat pumps have ratings from 7.5-9.0.)
But here is the real issue. Heat pump heating ratings are taken at an outdoor temperature of 45-47 degrees F. While we still need the heat to work at 45 degrees, how about 25 degrees? Or even 15 degrees and lower?
Let’s look at a performance chart.
The blue line is for a Trane XV18 heat pump. Not taking away from this unit as its performance is really impressive, but as you can see, when the temperatures fall, so does its heat output. As a 2.0 Ton unit, it should be making about 24,000 BTUs. But at 12 degrees, it is making only 15,000 BTUs (62.5%). Performance falls from there and it’s not even rated below 2 degrees.
When the outside temperature is really low and your heat pump falls in performance, it simply kicks on the emergency heat to make up the difference. Emergency heat is electric resistance heat and costs 3X more to run than the heat pump! In fact, if you were to convert the performance of electric resistance heat to HSPF, it would be 3.4. Effective, but expensive.
Now let’s look at a mini split – the red line in the picture. This Mitsubishi Hyper Heat wall-mount model is rated at 21,420. Look at this flat line. Wow. At 5 degrees F it still puts out 100% rated capacity. At zero degrees, it puts out about 92% of its capacity. That is about 19,620 BTUs! Some models from Mitsubishi do even better. Be careful too… other models are not rated for low temperature heat performance.
I have a similar Mitsubishi unit in my bonus room. It works flawlessly and has never left me wanting for more heat. Even during a serious cold snap for Eastern TN when it was 3 degrees outside, it was toasty warm inside. The rest of my house, with a conventional, high-end heat pump was forced to run the emergency for the entire week of really cold weather we had. My electric bill doubled that month!
So here it is… with the right mini split(s) in your home, your system may never need to rely upon emergency heat and your heating bills will thank you! A lot!
