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Minisplit placement and upstairs bedrooms

1910duplex | Posted in General Questions on

1011 Jackson St NEHi all,
From reading these boards over the last year or so, I’m pretty sure I want to install Daikin Quaternity, because in my 4a climate, it’s not the heat, it’s the humidity that makes sleeping uncomfortable. 

Background — I live in an old duplex with plaster walls and ceilings and radiator heat. We have lived without any air conditioning 97% of the time in the first two summers in the house, only resorting to sleeping in a room with a window unit (not our bedroom) when the forecasted low is in the high 70s or 80, so three to five days a summer.

My memory is that the temperature is often 84 degrees upstairs in the evening? It is frequently hotter in the bedrooms with the windows open and box fans going than it is outside at that time of night.

[Normal highs are 87 to 89 June 24-Aug. 18; normal lows around 70/71 same period; average dew point 67-68 in July & Aug.]

The smallest Quaternity is 9,000 for cooling, which I know from reading the boards here is considered too big even our largest 172-sq ft bedroom. (Second bedroom, which we also want cooled, is 145 sq ft.) Third bedroom is very small, under 90 sq ft, but is also attached to a former sleeping porch, now enclosed, but not heated, which is 54 sq ft)

Our bedroom is the front one on the second level diagram above, the largest; at times we will have foster kids in the second bedroom. Third bedroom is a home office, and last summer, we put a window a/c in the sleeping porch to cool that, but barely used it, because our desire not to add to global warming is stronger than our need not to sweat.

So, here’s the question: is it better to put a minisplit on the wall between the two major bedrooms and do some kind of short duct arrangement to have them both cooled by it? And then put a Midea modulating window unit in the sleeping porch to serve the home office? Or is the noise transfer between two rooms too disruptive to kids trying to sleep if we’re talking in bed?

According to earlier Q&A on Midea window unit, its 8,000 BTU window unit modulates down to 2,000 BTU, but usually runs a little above that and uses 147 watts.

I don’t know what size the GE window unit is that we currently have in the sleeping porch window, but I know 5,000 BTU is the smallest on the market. Is a too-big window a/c with an inverter better on power use than a smaller ‘normal’ window unit?

There is an extra deep closet in the second bedroom, whose back wall is shared with the third bedroom, which is 37 inches wide. Daikin unit is 35 inches wide. 

So should the solution be a minisplit in that closet to serve both those bedrooms, since noise is not an issue between them, and then put another unit in the main bedroom, even though 9,000 BTUs is overkill?

Is it a lot more expensive to run the coolant lines from interior walls out to the exterior wall? We are in a duplex, and the exterior wall is the left (East) side of the drawing above. If we did one unit to serve the master bedroom, it would go on the exterior wall. If it was serving the two bedrooms, the unit and/or vent would be directly above beds in both rooms.

Our attic is insulated at the roof line, and only runs a few degrees hotter than the second floor in the summer, however, it is fully floored, so I’m guessing ducting up there isn’t that practical? 

I don’t think putting one unit in the hall to serve the three bedrooms would be feasible, because the backside of the wall facing the door of the second bedroom is the staircase to the attic; moreover, I don’t think there’s even a way to run the coolant lines in that scenario, given that the exterior wall is on the opposite side of the duplex.

Not to mention that the fact that we won’t be cooling the downstairs at all seems like it doesn’t make sense to have the cooling in the hall, where it would mix more with the hot air rising from the first floor…

From writing this question, it seems the answer is there is no ideal solution, maybe just a least bad one!

For what it’s worth, we would probably find a 78 degree setting comfortable if the humidity was brought down to non-muggy levels.

Mara

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