Window A/C size question

[Gene4]

I have a 20'x28' 2-car detached garage with 9 foot high ceilings on a concrete slab. Walls are 2'x4' and the joists are 2'x10's, all on 16" centers. There is one window installed. I am in N. AL.

The walls will be insulated with R-13 faced bats and I'm looking at R-30 for the joists. Will also put something on the garage door. Not planning at this time to cover the insulation.

I am wanting to install a window A/C unit to keep this space at ~80 degrees during the spring/summer/fall months. The garage will be used for storage, no "work" will be done, so no extra heat load.

Would a 12,000 BTU unit be enough to handle this, or will I need to go up to the 15,000 BTU unit? My primary concern is dehumification.

Thanks for any advice!

 

[General Lee]

12,000 btu "might" be enough, it'll be close and it will probably run non stop. I have a 28x28 w/10' foot ceilings and run a 14,000 btu 120v. It does pretty good IMO.

 

[Richard Cranium]

go with the 14,000 110volt model or the 13,500 220 model any smaller you will freeze up the condenser and burn the unit up. A ceiling fan will help also.

 

[pattenp]

Getting an A/C unit too big is just as bad as getting one that's too small. A unit that's too large will cycle on and off too often and will not do a good job of reducing the humidity. Point is, bigger is not better. 13000 to 14000 btu would be about the right size for your garage.

See this link: http://www.energystar.gov/index.cfm?c=roomac.pr_properly_sized

 

[Gene4]

Lowe's doesn't give too many options. Only a 12000 or a 15100 BTU window unit in this size range.

 

[pattenp]

If those are your choices I'd lean more to the 12000 to make sure you get the most humidity reduction. Where there's a Lowes there's always a Home Depot. What do they have?

Lowe's doesn't give too many options. Only a 12000 or a 15100 BTU window unit in this size range.

 

[Gene4]

HD has a LG 14,500 and a GE 14,000 BTU unit in that 14k range. Both limited 1 year warranty. Couldn't find any reviews on them at HD site

Lowe's are Fridigaire with 5 year warranties standard. Seems to have reviewed very well. Sounds like the 12k unit is the way to go?

 

[Cobra6]

Do you have any interest in heat at all - or think you might?

I am in your neck of the woods with the same insulation in a 24' x 36' and I went with a combo AC/heater - Amana unit here - they have some other deals and free shipping.
http://www.appliancewarehousecenter.com/Amana_AHK18J_Electronic_18_000_BTU_Window_p/ahk18j.htm

They have pretty good pricing on other units. This one is a through-the-wall (TTW) unit but you can also installit as a window unit - something to consider. It is a little large for what you need, but they have around 14000 BTU
http://www.appliancewarehousecenter.com/Arctic_King_14_000_BTU_Thru_The_Wall_p/mww14crn1bi4.htm
(I think their pricing is messed up on this one)

There are a lot of options on the HD and Lowes web site

 

[Gene4]

Not really any need for heat(but good to ask about). However I will run a Dehumidifier during the winter months(when not needing the AC unit) to control the RH in the space.

 

[Tarheelgarage]

I just purchased a LG 1212 ER 12000 BTU window unit from HD for use in a family members house.

It uses a slide in seperate cabinet, has a remote, timer, etc. Also uses R410a gas. It is a 120v unit.

It is cooling a very large living room very well this hot weekend in NC.

 

[phbsales]

I did a rough load calculation for the OP. I don't know how many windows, exposures to sunlight, etc, but I'm coming up with about 16,440 btu output for cooling and humidity control.

Keep in mind, that the ratings on these window shakers are btu INPUT, not OUTPUT, so a 15,000 btu model might give you 13,900 btu output.

The OP also mentioned that he wanted to keep the space at 80*, so the 15,000 btu model might just be enough for the humidity control, due to the longer run cycle. The longer the cycle, the more humidity removal.

Anything larger than 15,000 btu will most likely be a 220 volt model.

 

[Gene4]

Thanks for the load calculation, very helpful! Here are some more details:

The garage has 1 standard sized double-pane vinyl window on the North side, and a door on the South side. The 2-car garage door(single unit) faces to the East. It is partially/mostly shaded in the late afternoon by a large Gumball/Sweetgum Tree directly to the West.

As you mentioned, the key is the humidity control. So it sounds like perhaps the 12,000 BTU may not be enough, and may just run overtime/constantly. Where-as the 15,000 BTU may be the better option? I am looking to stay with units running on 120 volts.

Are there any advantages to the 220 volt systems, or for that matter disadvantages with the 120 systems?

 

[phbsales]

Are there any advantages to the 220 volt systems, or for that matter disadvantages with the 120 systems?

Not really a whole lot of difference other than electrical supply requirements. Amp draws are a little less with the 220 volt units but is negligible. 120 volt unit should work fine.

 

[pattenp]

The 12000 BTU Frigidaire window AC that the OP was looking at is listed as having 12000 BTU’s of cooling. So how is that an input BTU rating?

I did a rough load calculation for the OP. I don't know how many windows, exposures to sunlight, etc, but I'm coming up with about 16,440 btu output for cooling and humidity control.

Keep in mind, that the ratings on these window shakers are btu INPUT, not OUTPUT, so a 15,000 btu model might give you 13,900 btu output.

The OP also mentioned that he wanted to keep the space at 80*, so the 15,000 btu model might just be enough for the humidity control, due to the longer run cycle. The longer the cycle, the more humidity removal.

Anything larger than 15,000 btu will most likely be a 220 volt model.

 

[phbsales]

The 12000 BTU Frigidaire window AC that the OP was looking at is listed as having 12000 BTU’s of cooling. So how is that an input BTU rating?

All manufacturers list their equipment based on input btu/h. Equipment is not 100% efficient so some btu's will be lost due to air infiltration, energy efficiency of the structure, equipment, etc.

 

[Falcon67]

Having used a 12K unit in my old 20x24 insulated in a very dry climate, you need at least 15K BTU, 18K would be better because of your humidity load.

 

[sirsloop]

I ran a 12K in my 24x24 last year (NJ) and it barely put a dent in the heat. The problem is most of the day I'm at work, the AC in the garage is off, and the entire area and all object in it get heat soaked. It takes A LOT of muscle to drop the temp down in a heat soaked room. Usually you get home and want to start a project right away. You don't wanna wait an hour for the AC to drop the temps in there from 100 down to 85, 75, whatever.

This year I added another unit giving me 24kbtu... and it seems to be cutting mustard. I would also like to install a ceiling fan to help move some of the air around.

My answer, MORE IS BETTER. 24Kbtu, plus ceiling fans. Get in, quickly knock the temps down with tons of AC, turn one of the units off, and maintain your working temperature.



If you want a single larger unit it will most likely run on 220V. My main floor AC unit is an 18.5k 220V Friedrich. Its a BEASSTTTTT!! Only difference with 220 is less amperage draw on the line. More volts = less amps. Not many people have 30A+ 110V circuits in their home, so the larger units use 220 to prevent someone from trying to run it on a 15A 110V circuit.

 

[Gene4]

I think I will go with the 15,000 BTU unit. I'm having a new 10-3 ga 30A line run out to the garage(to replace current 12-2 ga 20A line) so 1 phase will be dedicated to the A/C unit, and the other for the lights/power outlets. I don't need 220, as I'm not really doing any work out there. This unit will be running all the time, so it will only have to hold the preset temp I choose, rather than having to fight to get a hot room cooled down.

Thanks to everyone for this discussion.