Skinny Wall mount single room Air Conditioners

[rfsmith48]

Hey,

Thanks to all for the guidance on my Mini-Split questions.

Does anyone know of a small thru-the-wall unit that will fit between the existing wall studs? Implies an installed unit width of 14.25" (Max)

Thanks,

Rog

[Dana]

Most are designed to be installed in windows, and as such have window type widths. Any that would fit between studs would be 5000BTU/hr or less since a very narrow cabinet limits the size of the evaporator coil.

Mini-split solutions only make a ~3" diameter hole in the wall and are generally quieter, and start at 9000BTU/hr for the smaller units. Lesser-name 13SEER units run ~$750, but you can get high SEER high HSPF cooling and heating 9000BTU heat pumps like a Fujitsu Halcyon or Mitsubishi H2i for less than 2x that. If you're up for a DIY installation it's not rocket science, but it's good to have qualified tech test & fully commission it.

[rfsmith48]

Folks,

Thanks to all for the previous help and advice.

It looks like I will be installing a thru-the-wall conventional 115VAC unit in the master bedroom. (11 x 12 feet) Existing power circuitry is OK, I expect to add a dedicated branch power circuit. Wall is 2x4 stud wall with hardboard siding and drywall.

Questions: I have polled the LG, GE and Fridge websites, and none of them recommend a height position on the wall. Any thoughts? 5 feet or higher off the floor seems best.

Likewise, no recommendations as to the lateral positioning. I am thinking left of center, not directly over the bed. Comments?

Once again, thanks to all the commenters on this GREAT site.

Rog Smith

[jimbo]

For appearance and convenience sake, most are found mounted LOW, like below a window. For optimum COOLING performance, a higher mount is better. GE specifically make "high-mount" units, which has the controls in a LOWER corner, so you can reach them. These are in their tried and true AJ...series. There will be an "M" in 4th digit, indicating "mount". eg AJCM12... or AJEM12.... etc.

[rfsmith48]

Folks,

So I purchased a GE thru-the-wall unit and the Ge Case, RAB47A.

The installation instructions for the case do not talk about painting the case and (Obviously) do not recommend a paint spec.

Does anyone have any knowledge/experience with painting one of these cases? Are standard house paint products OK?

Thanks,

Rog Smith

[rfsmith48]

Folks,

Thanks to all for the guidance so far.

I installed the GE wall sleeve and tested it for drainage. (It drains OK)

The AC unit installed easily and we have been using it for about a week.

No water seems to be draining off the wall sleeve. The air in the room is cool and clammy. I bought a humidity gage (cheapy) from the local hardware store. It confirms that the AC unit is adding humidity to the room. Weatherunderground says that the external humidity is about 30%. Gauge agrees with that. Gauge says that internal humidity is about 50%.

I can't find anything in the GE User/installation manual to help diagnose this (Apparent) problem.

Any help is appreciated.

Rog

[Dana]

It's a physical impossibility for an air conditioner to add moisture to the air, but it can fail to dehumidify the air if it's cooling coils aren't running cool enough (below the dew point of the room air.)

When comparing weather data to interior air don't look at relative humidity, look at the dew point. Relative humidity is a meaningless number without the associate temperature it's relative to- it's simply a measure of how close the air is to saturation. But the saturation level varies with the temperature of the air. The absolute humidity or moisture content is measured by the dew point.

Say the outdoor air is 90F and 30% RH outside, the outside dew point is ~55F- cool that same 55F dew point air (without removing or adding moisture) to 75F and it's relative humidity becomes ~50% without any change in the moisture content. Cool that same air down to 55% and it's at 100% relative humidity. Same air, only the temperature changes.

You can get this info off a psychrometric chart, or use an online psychrometric calculator.

But since the cooling coils on the AC unit SHOULD be well below 55F, water should be condensing on them, drying out the air. At it's lowest blower speed, try to measure the output air temp with a bulb thermometer. If it's putting out air no colder than 60-65F air at low speed it's likely the refrigerant charge or volume control is off. At lowest blower speed the coil runs cooler, which condenses more water out of the air, but some high SEER models at high speed don't do much drying at high fan speed.

FWIW: 50% RH @ 75F is a perfectly healthy indoor humidity, but above 60% it's less comfortable, and fungus/mold risks begin to rise. Those with dust mite allergies are advised to keep it at 50% or lower, since dust mites can't reproduce at that humidity level, but most people are just fine up to 60%.

[jadnashua]

Having too large of a capcity a/c unit can limit how much dehumidifcation it can do since it doesn't run long. Ideally, you want one that can run constantly to continually run the air over the cold coils and draw moisture out. An excessively large one only runs a short time, then shuts off, not giving enough of the room air a chance to run across the coils and have moisture extracted. This is why you are better off with a slightly small unit verses a bigger unit than needed, so that it can dehumidify. Nothing worse (to me anyway) than being cold and clammy. That shouldn't happen if 'right-sizes', or it is slightly small. It can with one too big. Now if you lived in the desert, you might not care as much as if you lived in someplace like Tampa, FL.

[Dana]

Outdoor dew points in CO are pretty low compared to the eastern US, so I wasn't thinking a small through wall AC unit would ever be so oversized as to not keep up with the latent load, but maybe.

If this is the tightest house in CO moisture buildup from interior sources could be an issue.

In my house the sensible load is rarely enough for the AC to dry the house out, so I run a dehumidifier, but in MA the latent loads are substantial compared to CO.

[rfsmith48]

Guys,

Thanks for all the good info. I gotta admit that I am a Mech. Engr, (PE as well) but thermodynamics is not a strong suit...(Grin)

My unit has a "fresh air" vent, that I am currently running open. The GE manual does not recommend either setting for this vent. Can someone comment on the positives/negatives of either setting?

Thanks,

Rog

[jadnashua]

Fresh air mixed in will increse your costs a lot, and, if the humidity is high (may not happen in CO), you'd constantly be adding that hot humid air to the mix, then try to cool it and remove that moisture.

[Dana]

What Jim said, to which I'll add:

In vent mode the indoor air's humidity will track that of the outdoor air, but when unvented running the AC will lower the indoor humidity, which is generally better for comfort.

Using a wall-mount or window-mount AC as a "ventilation system" is a mediocre way to get ventilation air at best, and unless you have a lot of stinky-sock or cigarette smell to purge from the room you're better off closing it to get lower indoor humidity, lower indoor pollen count, and lower operating cost.

[jacobsond]

I dont think I saw what size unit you bought.Like previously stated to large of a unit will get you a cold humid room.The GE RAB shell will hold different sizes of ACs.The AC only dehumidifies when the compressor is running.Looking at your room size I would guess an 8000btu would be about right.Dont worry about it not dripping on the outside most window air units hold about an inch of water in the pan.Then the condenser fan blade slings the water up onto the condenser coil.That helps efficiency.Leave the vent closed that just brings in warm moist air.

[rfsmith48]

Unit is 8300 BTU's.

I closed the vent.

Thanks, guys.