Ductless Minisplits vs Mr. Cool Universal
Hi everyone,
I feel like iterations of this question have been asked dozens of times on this forum, but I am seeking clarity on some of the nuances of my particular decision.
I am building a small (1305 square foot) 3 bedroom 2 bath 1.5 story house in zone 6 to code (Nominal R-49 sloped ceiling, R-23 walls, R-15 Crawlspace walls hopefully under 1. ACH @ 50 pa). I would like to provide heating AND cooling. Heat pumps are attractive as they are the only efficient option since I don’t want to connect to gas (not morally opposed, just trying to limit utilities if possible). I am also enticed by the potential to install either the air handler or ductless version of a Mr. Cool unit by myself. In terms of fresh air, I am pretty set on the three pairs of Lunos HRVs or something conceptually similar because for such a small home it seems adequate. Adding an HRV/ERV to existing ductwork seems like whatever efficiency one gains by the heat exchange is lost by relying on the blower fan to distribute the fresh air every hour.
So, here are my choices:
Option 1: Mr. Cool 24k btu with 10kw heat strip in the crawlspace with ducts. This system provides dust filtration, and ducts are what most people do (which makes me feel obliged to do the same), but the ductwork design, even though it appears well-designed, is the opposite of elegant. Since I plan on doing this myself, anything that looks like a lot of tedium gives me pause.
Option 2: Mr. Cool 2-zone 12k heads, one on each floor, with baseboard back-up heaters. I would probably supplement this with a stand-alone dehumidifier and air filter. Summer evenings are generally cool, but humid, and I want to somewhat compensate for the lack of a furnace filter in the absence of a furnace. A little convoluted in terms of the accessory appliances, and backup heaters, but less so (in my opinion) than snaking ductwork.
Which would you do? Or should I consider a third mystery option? My ultimate goals are unsurprisingly comfort, affordability of operation, and general efficiency. Any resources to suggest or approaches to consider are welcome.
Thanks!
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Option 1 provides cooling to every room and option 2 doesn't. Replacement will be easier, it provides filtration, and it provides dehumidification. It's the clear better solution imo. You might look at splitting it by floor if the ductwork to get to the top floor is too challenging.
What's the heat loss here? If you're on 100 amp service, dedicating 10kw to resistance is a pretty big deal and seems large for a house this size and insulation.
Thanks! I think our design load was around 34k btu/hr. and 24k cooling. Both seemed over the top to me, but what do I know?
I’d sort that out first! 2 tons cooling in zone 6 for that size home is extremely suspicious.
The lower the heat load is, the smaller your ducts have to be, so it’s important to get that right.
More mechanical units, more maintenance. Each of the mini-split heads has to be cleaned separately. I don't mean cleaning the filters, although those are a pain as well (wash off every 2 weeks?) I mean chemical cleaning with the big bags trying not to get wet cleaning fluid/dust on everything. People in Austin are charging $200 a unit for those cleanings and (for us) they were needed every 18 months.
More units mean more opportunities for fans to break, dust to build up and unbalance the units. There is also a lot more creaking from the refrigerant lines than many people expect. It's also more opportunities for refrigerant lines to leak. Drains clog too.
If the 2-zone units are misbalanced (overheat/overcooling from spillovers from the other units operation) there is very little you can do, unlike ducts where you can use dampers to re-balance simply.
Food for thought :)
The cleaning and maintenance were not things I had given much thought to. Thanks!
Multi-splits have a bad rep here because they have limited turndown ratios (usually ~50%), leading to more energy consumption than advertised and worse comfort. You would be better served with 2 single-zone mini-splits. It will have vastly superior turndown, zoning, and efficiency.
Zone 6 is cold so you likely need a bigger load on the ground floor vs the second floor, instead of equal-sized units. Ducting has lots of advantages: you can tie in ERV, dehumidification, filtration, and circulation. Given that these are concerns for you it seems like a clear winner to me.
If you have a relatively open ground floor, I would suggest having 2 systems: a slightly undersized whole house ducted unit for all the air management, while having an 18k ductless single-head mini-split in the ground floor that will handle the bulk of the load. Two systems also provides redundancy, extra capacity, and I don't think heat strips or electric baseboard would be needed.
This. 2 high efficiency single zones is the way to go.
I have a 12k Gree Sapphire single-zone connected to an Emporia Vue and have verified the performance numbers in the attachment.
My neighbor has the exact same house as mine and I consistently use 50-60% less electricity than his 4 zone multisplit.
These high efficiency single zones can turn down low and only use 100-200 watts while delivering stunning COP's.. No multi split or ducted unit comes even close to that kind of efficiency at minimum capacity.
Thanks! This is an interesting idea I had not really considered. What climate zone are you in? Heat pumps beat baseboard heaters handily, but, as you probably know, at very low temps they just turn off.
"Heat pumps beat baseboard heaters handily, but, as you probably know, at very low temps they just turn off."
How "low" are you talking about for it to "just turn off"? If you are posting on this forum I assume you already know this, but many people do not -- low temp heat pumps these days can do pretty well all the way down to well below 0 degrees F. If you didn't know that, look up Mitsubishi Hyperheat and Fujitsu's competitor product (can't remember the name off the top of my head).
My heat pump doesn't turn off at low temperatures, it supplements with resistance strips.
Zone 6 in New England. The other benefit of these high efficiency single zones is they have some of the best cold weather performance.
Both my single zones are rated 79% capacity to -22. I've been through many subzero nights with them with zero issues.
Attached is the performance chart to -22.
BFW577: I've never heard of Gree. How did you come to choose them?
(After looking it up, an Emporia Vue is a whole home energy monitor).
Rocksteadily: Are you considering any type of supplemental heat for bathrooms, like maybe an electric heat matt under tile floors?
It was one of the most efficient single zone mini splits in the AHRI directory. The 9k version of my unit is rated 38 SEER 15.5 HSPF. Midea/Carrier have the most efficient unit available at 42 SEER.