MrCool 3rd Gen VS 4th Gen DIY: SEER, HSPF Comparison

In June 2022, MrCool presented their newest 4th Gen DIY mini splits. Effectively, it made the beloved MrCool 3rd Gen mini splits an older version of mini splits. Let’s look at how the new MrCool 4th Gen units differ from the now older MrCool 3rd Gen.

mrcool 3rd gen 24k outdoor unit on a lawn
This is the MrCool 3rd Gen 24k outdoor unit (that does all the important heavy lifting). Seems pretty OK, works great, but the new 4th Gen units are even better.

Obviously, we are going to do this based on specs + features.  If you open the specs, you can see that there are 4 key differences between MrCool 3rd Gen and 4th Gen:

  1. SEER Ratings (Cooling Efficiency). This is the most important difference; the MrCool 4th Gen have higher SEER ratings, making them more efficient and cheaper to run.
  2. HSPF Ratings (Heating Efficiency). This is especially important for heating; the MrCool 4th Gen units have higher HSPF ratings, and thus provide cheaper heating. HSPF is often overlooked; but it’s arguable even more important than SEER rating since heating is often much more expensive than cooling.
  3. MrCool DIYPro MC Cable. MrCool 4th Gen includes this communication cable between the indoor air handler and the outdoor condenser. This eliminates much of the electrician’s work you needed with the 3rd Gen; it’s frankly a very convenient addition for DIY installation.
  4. Price. The 4th Gen is the newer model and thus obviously a bit more expensive. Example: If we compare the basic 12,000 BTU mini split models, the 3rd Gen cost was about $1,400. You can check the current 12k 4th Gen cost here; it should be about $1,700. So, we see that there is about a $300 cost difference between the 4th and 3rd Gen MrCool 12k mini split (that’s a good +20% price difference).

Quick Note: When checking the SEER and HSPF increases (cooling/heating efficiency), we can arguably say that the 18k unit (4th Gen) got the highest energy efficiency increases. For everybody thinking about buying the 4th Gen MrCool DIY mini split, the 18k unit does have the highest SEER and HSPF ratings, they really did a great job with that unit.

mrcool 4th gen outdoor unit produces more efficient cooling and heating
As with all mini splits, the outdoor unit (condenser) is responsible for cooling and heating efficiency (measured by SEER/HSPF ratings)

All other things are the same:

  • Same good warranties.
  • Same sizes (12k, 18k, 24k, 36k) as well as multi-zone units (up to 5-zone mini splits).
  • Same low noise levels (4th Gen units might be a bit quieter; the difference is only 1 dB or 2 dB only).
  • Same somewhat lacking customer support? That’s the one bad thing to point out with MrCool mini splits, hope they will improve that with the 4th Gen.
mrcool 18k 3rd gen diy unit label on outdoor unit
Specs on the outdoor unit label like max fuse, use of R-410A refrigerant, design pressures, min. ampacity and so on are almost exactly the same as well. This is an 18k 3rd Gen unit. Both 3rd and 4th Gen units are made in China, no difference there.

Alright, let’s check the SEER and HSPF rating differences for the 3rd vs 4th Gen unit. We will also look at how much less it costs to run the new more energy-efficient 4th Gen mini split heat pumps (to see if the 20% cost hike pays for itself with efficiency):

MrCool 4th Gen Has Higher SEER Ratings Than 3rd Gen (Cooling Efficiency)

Now, comparing 3rd Gen SEER with 4th Gen SEER is not as simple as it used to be (it’s not SEER vs SEER, it’s actually SEER vs SEER2). Namely, the DOE started using a new SEER2 rating (you can read more about this new AC cooling efficiency rating here). In simple terms, a 14 SEER rated unit now has a 13.4 SEER2 rating.

Example: 24k MrCool 3rd Gen unit has a 20 SEER rating. The new 24k MrCool 4th Gen unit has a 20.5 SEER2 rating. You can see why this might be confusing.

To completely un-cofuse it for everybody, we will use this SEER2 to SEER conversion. We see that the 20.5 SEER2 rating is about equal to the 21.5 SEER rating. Now we can see that the new 4th Gen 24k unit (21.5 SEER) is 7.5% more energy efficient than the old 3rd Gen 24k unit (20 SEER).

Here is the head-to-head SEER rating comparison between MrCool 3rd and 4th Gen units, with 4th Gen SEER2 converted to SEER rating:

MrCool Mini Split Capacity: 3rd Gen SEER Rating: 4th Gen SEER Rating: Percentage Diff.:
12k Unit 22 SEER 23.6 SEER (22.5 SEER2) 7.3%
18k Unit 20 SEER 23.8 SEER (22.7 SEER2) 19.0%
24k Unit 20 SEER 21.5 SEER (20.5 SEER2) 7.5%
36k Unit 16 SEER 19.1 SEER (18.3 SEER2) 19.4%

Note: All the data here are from MrCool 3rd Gen DIY brochure here and MrCool 4th Gen DIY brochure here.

As we can see, the 4th Gen unit have a noticeably higher SEER rating. It’s especially nice to see that the 36k unit – which was only 16 SEER and we advised against it, based this rating – has gained almost 20% in cooling efficiency (with new 19.1 SEER rating, quite good).

The 4th Gen 18k unit also gained a lot of efficiency.

Here’s a quick example of why these 4th Gen higher SEER ratings matter:

Let’s say you need a 36k unit. For cooling, you will run it for 1,000 hours per year, and let’s say the price of electricity is $0.15/kWh. Here are the numbers for 3rd vs 4th Gen 36k unit (this is the difference higher SEER makes):

  • 3rd Gen 36k unit will consume about 2.25 kWh every hour of cooling. That’s 2,250 kWh per season with a $337.50/year cooling cost. In 10 years, that’s $3,375. In 20 years, that’s $6,750.
  • 4th Gen 36k unit will consume about 1.885 kWh every hour of cooling (less electricity usage due to the higher SEER rating). That’s 1,885 kWh per season with a $282.75/year cooling cost. In 10 years, that’s $2,827.50. In 20 years, that’s $5,655.

As we can see, the new 4th Gen 36k unit will produce the same amount of cooling as the 3rd Gen 36k unit, but the cooling bill will be about $54.75/year lower (due to the higher SEER rating 4th Gen units have). That’s about $500 in savings in the next 10 years, and about $1,000 in electricity savings in the next 20 years.

Knowing that the running cost is a bit lower does justify that 20% hike in price, all things considered (and, of course, there’s the inflation as well).

We looked at the SEER rating that concerns the cooling part. Let’s do the same for the heating part by looking at the HSPF ratings:

4th Gen Units Also Have Higher Heating Efficiency (Higher HSPF Ratings)

All MrCool mini split heat pumps can both cool and heat. What SEER rating is for cooling efficiency, HSPF rating is for heating efficiency. You can read more about HSPF or Heating Seasonal Performance Factor here.

Now, let’s start with an example to illustrate that we will also face the HSPF vs HSPF2 rating here (it’s not an apples-to-apples comparison).

Example: 3rd Gen 12k unit has a 10 HSPF rating. 4th Gen 12k unit has a 9 HSPF2 rating. You can already see that we have this HSPF vs HSPF2 confusion.

We will need to convert the new HSPF2 rating (adopted by the DOE is 2023) to the old and familiar HSPF rating. The easiest way to do that is just to use a 15% rule of thumb (if you add 15% to HSPF2, you get the old HSPF rating). We have done the analysis for this conversion here.

That means that the 9 HSPF2 rating is about equal to the 10.4 HSPF rating. We see a 4% increase in heating efficiency in favor of the 4th Gen 12k unit. Here is the full 3rd vs 4th Gen head-to-head heating efficiency comparison for all unit capacities:

MrCool Mini Split Capacity: 3rd Gen HSPF Rating: 4th Gen HSPF Rating: Percentage Diff.:
12k Unit 10 HSPF 10.4 HSPF (9 HSPF2) 4.0%
18k Unit 10 HSPF 11.3 HSPF (9.8 HSPF2) 11.3%
24k Unit 10 HSPF 10.6 HSPF (9.2 HSPF2) 6.0%
36k Unit 8.9 HSPF 9.2 HSPF (8 HSPF2) 3.4%

We got this data from the same 2 brochures we quoted earlier.

Again, we see that the 18k 4th Gen unit got a big 11.3% increase. That’s quite a lot in terms of heating efficiency. All 4th Gen unit sizes have a higher energy efficiency; this is great to see.

Alright, let’s illustrate how this superb 18k 4th Gen unit compares to the 18k 3rd Gen unit in terms of electricity usage and cost with an example.

Say that we are looking for an 18,000 BTU heat pump for heating. We will run it for 1,000 hours per year, and the cost of electricity is $0.15/kWh. Here are the average electricity usage and running cost numbers for 3rd Gen vs 4th Gen mini split heat pumps:

  • 3rd Gen 18k unit will consume about 1.8 kWh every hour of heating. That’s 1,800 kWh per season with a $270/year heating cost. In 10 years, that’s $2,700. In 20 years, that’s $5,400.
  • 4th Gen 18k unit will consume about 1.593 kWh every hour of heating (less electricity due to a higher HSPF rating). That’s 1,593 kWh per season with a $238.95/year heating cost. In 10 years, that’s $2,389.50. In 20 years, that’s $4,779.

We can see that the 4th Gen 18k unit will produce the same amount of heat as the 3rd Gen counterpart, but our heating bill will be about $30 per year lower. That’s $300 in 10-year savings and about $600 in 20-year savings.


You know how the iPhone 15 is just almost the same as iPhone 14 with a tiny better battery, a bit slimmer, a bit better camera, but quite more expensive? Yeah, this is not the deal with the 4th Gen vs 3th Gen MrCool mini splits.

The 4th Gen does provide serious improvements. The key improvements are higher cooling efficiencies (SEER rating up to 20% higher; thus up to 20% lower cooling expenses) and higher heating efficiencies (HSPF rating for 18k unit is increased by 11.3%; quite a lot for heating efficiency).

The nice-to-have improvement the 4th Gen units have is the MrCool DIYPro Cable. This is a communications cable between the air handler (indoor) and condenser (outdoor) that goes through the wall. A lot of DIY people will love this, especially those who hate playing around with electrical wiring.

The price increase from 3rd to 4th Gen is about 20%. Yes, that’s substantial, but inflation obviously has a role to play here as well. The key thing is that with our spec-by-spec analysis, you see you are not just buying a repackaged 3rd Gen unit with a 20% price hike just because MrCool can do that.

The 4th Gen units are actually notably more energy efficient. This will lower the electricity usage (compared to 3rd Gen units), lower your cooling/heating bills, and after about 10 years, the price hike pays for itself due to these higher cooling and heating efficiencies 4th Gen has.

Hope this was helpful, and thank you.

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