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Ive learned a lot about Mini Splits. But I still would appreciate some expert advice please. Ive narrowed my choice down. But I don't know which is better: single zone or dual zone.

A few specs for my house: I'm in Arizona, elevation 6,500 ft. Low temp -3 F High Temp +/- 100 F. The house was built in 1934 and is 683 sq ft. (It's tiny). There is no duct work or system of any kind for cooling. Heat is propane space heater from the 70's. I'm looking to put 2 wall mounted units in Rooms the size of: bathroom/ office 11 x 9 & LivRm/ kitchen 24 x 14.

Does it make more sense to go with a multi-zone unit (single outside compressor) or two separate units (one for each room)? Which one is cheaper to run long-term?

One last question: Where could I find an estimated cost increase to my electric bill post install? Just to give me an idea what to expect when the bill arrives..Thanx for the help

  • Presumably a single dual zone would be cheaper than two single zones since there would be only one condensing unit. Are you finding this true? But there would be more protection from failure with two independent condensing units. How many air handlers are you going to have--two or more than that? How are you going to pipe away the condensed water? Are the air handlers all going to be on an outside wall? What is the electric power/current requirement for these 120 V units? Will you have to add circuits to power them? Will the condensing units be on the ground or on the wall. – Jim Stewart Jun 26 '17 at 17:08
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    To keep this away from product recommendation, I re-worded the bulk of the question to focus on multi vs two separate units, and removed product links. – gregmac Jun 26 '17 at 19:48
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This skates awfully close to a shopping question - but. What I have observed in my consideration of the same question is that the most efficient units are essentially always single-zone. This makes a degree of sense, as an outdoor unit that can run 2 (or more) inside units will be oversized when less than the full number of units are calling for service at the same time.

That is treating the running cost as a prime motivator (which I do) - purchase cost can be and is all over the map, but is more often in favor of a multi-zone system.

The factor of not having a single point of failure for the entire system is also a consideration, as @Jim Stewart points out in a comment. Systems do fail or require maintenance, and there's a big difference between everything not working and half of things not working when that happens.

If you have no A/C now, your electric bill is hard to predict, considering no information about insulation (probably bad at that era unless it's been upgraded) and sun exposure. If you use window units now, very probably the cost will go down, so long as the mini-splits are more efficient (higher SEER) than the window units.

I note that only one of your brands expresses a SEER number as you're presented them to us. You should find out what the other one's SEER rating is, as that greatly influences the cost of operation.

Relative cost of heating with the mini-splits .vs. propane will depend on the price of each fuel and efficiencies.

  • My apologies for unintentionally straying outside the sites guidelines. And my thanks for not deleting my question entirely. As the leftover portion was my main goal. Not the product recommendations. – AzTrifecta Jun 30 '17 at 19:43
  • To answer Gregmac's questions: There would be two airhandler units. Both placed on outside walls. The condensed water runoff would be up to the installer (im not sure). I believe I have a 220 circuit available already to utilize. The condensing unit would be on concrete slab on the ground in mostly non direct sun. – AzTrifecta Jun 30 '17 at 19:50
  • To Ecnerwal: thank you for all the helpful information you provided. The two single units have SEER's of 17 & 17.5. The dual unit SEER is 20.5 for the condenser. The airhandlers are 22 & 23 SEER. Are these differences significant enough to make a large difference in the running cost? Would that outweigh the single point of failure factor? And yes you are correct about the insulation. The attic has insulation, but walls have literally none. The sun exposure is minimized by pine trees & 6800 elevation. Thanks again for the helpful info, it's greatly appreciated :) – AzTrifecta Jun 30 '17 at 20:07
  • Unimpressive numbers for single-zone units. Shop around more. For those pathetic numbers the dual unit is about 18% more efficient (will use that much less electricity for the same cooling.) But you have to consider the up-front cost and your electricity cost (though you should also look into any electric company rebates for getting a more efficient unit, and you should definitely consider insulation, as going from "none" to "any" pays back quite fast.) – Ecnerwal Jul 1 '17 at 2:12

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