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I'm in the high desert of Southern California. We're in a 2300 sq foot home, 2 stories with 3 bedrooms and 1 master bedroom on second story. The house is cooled by 2 central air systems, manufactured in 1990. The second story is cooled a Rheem Classic X Rahe-030jas, with the tag in the picture below. Supposedly its 208/230 Volts, 18 Amp single phase. Google says its SEER rating is 10. I'm thinking of putting Honeywell a portable mn10cesww, 10000 BTU (ASHRAE-128 Standard) / 5500 BTU (DOE+ 2017 Standard), in the master bedroom, and two bedrooms, and not running the central air at all this summer. I care only about cooling those 3 rooms. Plus I already have a small window unit in the a 4th bedroom/office, that's rarely used. The central a/c also cools the hallway and bathroom on the second story.

Will running the portables in each room at night be more efficient than running the older central air at night, especially considering that they won't be running when nobody is in the room?

Also as far as the first story goes, we never run the central air. We only cool it with a 14000 BTU portable unit.Current unit Honeywell unit under consideration

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    Have you considered having the central system redone, and/or having the house air-sealed and/or insulated? (Also, check your attic: if the indoor unit and ducts are up there, then that's a big chunk of why your central A/C is terrible)
    – ThreePhaseEel
    Commented May 26, 2019 at 23:29

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My guess is that the three portables would use less electric power than the single old central unit. But the central unit is cooling and drying out the bathroom and you might have moisture problems without it blowing dry air into the bathroom.

So you want to put in three 10 kBTU/h portables, one in each bedroom, for a total of 30 kBTU/h, and you want to know if this would be more efficient that the existing old central unit which cools the second story. It is a 30 kBTU/h R-22 unit manufactured in 1990 and was rated at 10 SEER when new.

(1) What is the SEER of the portable unit? Presumably much high than 10, but you need to know what it is. The portable runs on 120 V, right? Do you know what the running current is?

(2) Is the portable a one hose or a two hose unit? If the unit is only one hose, then there would be a net pumping of air from inside to outside. This would result in air infiltration from outside to replace the air pumped out. Two hose units are better because they get the condenser cooling air from outside.

EDIT

What is EER rating for AC units? The air conditioner EER is its British thermal units (BTU) rating over its wattage. For example, if a 10,000-BTU air conditioner consumes 1,200 watts, its rating is 8.3 (10,000 BTU/1,200 watts). The higher the rating is, the more efficient the air conditioning unit is.May 1, 2019

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  • Efficentcy on the portable is 9.5 EER. 9.5 Amps --> 1050 Watts. This seems less effient than the almost 30 year old central air unit by RHeem. However reeding the Rheem manual at mail.rimsupply.com/pdf/a11_147.pdf it says 30,000 BTU/HR [8.79 kW] and 208-230 Volts -1-60. The rating for this unit is SEER but I'm not sure how that relates to EER. Seems like the old Rheem would by 30000/8790 = 3.3 EER but that just doesn't seem right.
    – Frank
    Commented May 27, 2019 at 3:13
  • The sticker on the central unit says the compressor draws 13.9 A at 240 V so 3.34 kW. The EER would be 30 kBTU/h / 3.34 kW = 9.0 . I don't know if the EER is supposed to take into account the energy consumption of the cooling fan in the condensing unit and the air handler inside.
    – Jim Stewart
    Commented May 27, 2019 at 12:05
  • So it's kind of seeming "iffy" whether or not the 3 1050 Watt portable units will be more cost effective than the 30 year old central a/c. This is disappointing. I'd expected it to be much better.
    – Frank
    Commented May 27, 2019 at 18:09
  • What about using window units? Are your windows vertical moving (single or double hung) or are they horizontal sliding? In some cases window units are prohibited by HOA regs. They can block egress in case of a fire. They can be a target of theft.
    – Jim Stewart
    Commented May 27, 2019 at 20:05
  • I believe the ultimate in efficiency is the "mini-split". Some of these are advertised as 20 to 30 SEER. All that it takes is a 3 inch diameter hole in a wall. The installation is not DIY however, unless one is very capable. Some require 240 V but others work on 120 V.
    – Jim Stewart
    Commented May 27, 2019 at 20:10
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I can't provide product specs, but can share that when my central AC died last summer in a heat wave I bought a couple of very small (I could lift and install by myself) window units. $tressed about fixing central - until my electric bill came in at a fraction. Similar, only need to cool a couple rooms to be comfortable

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  • I have investigated this too for a relative whose old central unit died. I think cooling a house with modern window units is much cheaper than a central unit. The current draw of modern window units is amazingly low. These do block windows and don't fit easily in side sliding windows.
    – Jim Stewart
    Commented May 27, 2019 at 12:09
  • I would consider window units, but my wife is dead set against them. Just looking, it doesn't seem that the portable units are as efficient as the window units.
    – Frank
    Commented May 27, 2019 at 18:29

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