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Heating & Air Conditioning

Ductless A/C and heater question

5 years ago

My house is in San Francisco bay area. My living room (262 sq. ft.), dining room (192 sq. ft.), family room (128 sq. ft.), and kitchen (138 sq. ft.) are connected without doors. More specifically, the dining room and family room are next to each other in a rectangular shape. The family room has a narrow entry (about 40") to dining room. I plan to install two indoor units, one in the living room and the other in the family room. For such space, I wonder if 9,000 BTU each would be enough. Or, I should go with 12,000 BTU each and use a 24,000 BTU outdoor unit?

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Comments (5)

ionized_gw
5 years ago
You need a complete load calculation to say for sure. The quality of the air sealing, how much insulation and the nature and number of your windows can all have a large effect on equipment sizing.

When it comes to deciding if you want one or two outdoor units, check cost both ways. Having two adds redundancy, but could also add repair costs. For variable speed systems, the 1:1 will allow you to run at lower capacity than one large one when you are running one indoor unit. Putting it another way, running one indoor unit at times of low demand will result in cycling on and off more with one large outdoor unit rather than two. Constant running at low speed yields better humidity control than snapping on and off.
Thomas Tzeng thanked ionized_gw
mike_home
5 years ago
The summer design temperature for San Francisco is about 75 degrees. The area to be cooled is about 720 sq. feet. I would think one ton of cooling would be plenty.

You could save yourself a lot of money and install two 8,000 BTU window units.
Thomas Tzeng thanked mike_home
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ionized_gw
5 years ago
Maybe you have already done this, but rereading the comments, it jumps right out at me now. I am combining mike-home's suggestion of window units with the need to determine the capacity that you need. Sometimes load estimates are very good and sometimes they are way off. Sometimes they are way off because it is impossible to get a good number for how good insulation and are sealing are, or some other parameter. I suggest that, if you can pull it off, run with a couple of window units for a time with heavy demand. Get data for a few weeks, at least. Pay attention to, or somehow meter, how much the units are running. That way you can have the best possible estimate given the capacity of the window units is accurate.
weedmeister
5 years ago
With the Bay area, you have micro-climates. It might be 75f in one area, and 95f in another.
Thomas Tzeng thanked weedmeister
Thomas Tzeng
Original Author
5 years ago
I live in south bay, San Jose. I feel A/C is not a concern for me. Here, the weather is so good that we only turn on A/C in a few days. Heater is my main focus. I got an estimate from one company. It suggests a 6-to-1 system for the whole house about 1,600 sq. ft. The out door unit is 48,000 BTU. The two wall mount units in family room and living room are 9,000 BTU each. My own calculation based on online load calculator, living, dining, kitchen, and family room need about 20,000 BTU heating load.

Another question in my mind is that for ductless minisplit system, is it enough to cover the hall bathroom and master bathroom by using indoor units in the living room and the master?

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