Help Please

[Char-Gar]

In the next couple of months I will begin the process of remodeling my garage into a shop. I live in deep South Texas and need a window air conditoner. It will probably be used 300 days a year in a high humidity environment. The garage is 20 X 20 feet. I need to know what size of unit to buy. How many btus and what kind of wiring. Any help will be appreciated. Thanks

[dragonrider]

Assuming you will insulating the garage, I would go with a 220V unit, at least 18,000 btu. Be sure to get a unit that will turn itself on and off as needed.

[Buckshot]

..............I'd ask Mt Gianni as he's in that business. However what I did when specing a unit for our 24x20 master bedroom addition was just to go online to the various manuafcturers and took a look at what they had. Plus there are places online wiht FAQ's and Q&A sections and e-mail Q&A. We'll be using a heat pump.

I'm sure you'll be looking at a 220 V system. Also efficiency costs money as does warrenty length and coverage. You need to balance your electricity costs against performance, but buying the most efficient you can afford along with the warrenty would never be a big mistake.

My daughter had her 2 story Queen Ann cottage (built in 1894) setup with forced heat and air. She had to go with 2 seperate systems (upstairs and downstairs) due to ducting issues. She had 3-4 contractors give her bids and they ranged from $8800 to $23,000. California has a minimum SEER requirement, which is a measure of efficiency. As is probably common, she went with a system that cost about mid-point at $14,400.

It was a few SEER points over the state minimum but most comforting to her was the fact that it had a 20 year parts and labor warrenty for the entire system.

................Buckshot

[felix]

Charles, your killer down there will be condensation. This means everything will rust if kept in the garage if you do not maintain the cool round'the'clock. The implication is that you will need insulation to keep the power bill down, and have minimum air leak to the outside. Allow venting to come through the house, which is also air conditioned, if garage is attatched. Water elimination will come off of cold coils as you know. If everything is Kosher in terms of this, then 18000 BTU will be fine. If garage is detatched and doors opened often, or there is an intentional leak to get air into the area for casting exhaust, then you'd best get a dual range machine, like 18000 BTU in combo with another at 12000 BTU for overload conditions. The gadget will operate based upon demand like normal. Ideally, you want the "total" machine to not run more than about 20 minutes per hour to keep the humidity at 35-45 percent. Remember, you have salt air in your area, and that will increase the corrosiveness of any condensation. ... felix

[S.R.Custom]

Will you be keeping guns, safes, etc. in this garage? If so...

A garage is a slab-on grade proposition, and unless measures were taken at the time of construction, you will have moisture migration from the ground up through the slab. That coupled with the high humidity in the air will more than likely require a means to remove humidity from the air those 65 days where cooling is not desired. (This is all roundy-round architect-speak for the fact that you'll probably need a dehumidifier, too.)

[Morgan Astorbilt]

Don't go overboard on the BTU's. You want the unit to run long enough to also remove the moisture. Too high a BTU rating will cool the area and turn off, before the moisture is pulled out by condensation.
Morgan

[MT Gianni]

What Morgan says is right. My area is much more into heating than AC as it's been 30 years or more since we have owned AC. We just live where you can keep the windows open the 45 days or so that you need it.
Furnaces are tested for efficiency by AGA after running for 1 hour. This is the number they get to put on the side showing the EER % that the customer will see. To get to max. effiency your unit needs to run at least 3-5 minutes per compressor cycle. {not fan time disregard what the fan is doing}. Insulate with all you can fit in the walls R11 or 19 depending on their thickness, use a tyvex blanket wrap if you can and take the square footage and area measurements to where you buy your window unit. They should be able to do a heat loss calculation or heat gain in your case and explain to you the results. I would not go with an oversize figure of more than 15-20%. What I mean is, if your heat loss is 15,000 BTH per hour [btuh] then it will need +15% to keep up on the hottest day of the year. A factor of 10% to 25% is then added to cool it from that max temp. If the power was out and garage temps were at 90 you would want to drop temp not solely maintain them. Too much will cool faster but at the cost of everyday effiency.
Look at a small air to air heat exchanger as an efficient way of removing moisture when you are not cooling. Factor in how often you will use a walk-in door and how long it will take to recover from having the roll up doors open and closed.
Most of all enjoy your hobbies and upcoming retirement. Gianni

[MT Gianni]

If you go with a contractor installed rather than a window unit for warranty reasons I would consider who you want in your shop as a bigger factor than price. There may be somethings in it that you would not want as public knowledge. Gianni

[454PB]

When I built my shop/reloading room, I had the partitioned area for the loading room super insulated. This room is 12 feet by 24 feet, so about 70% of the same size you mention. My issue is cold, not heat. Since you're going to be running air conditioning that much, $1500 worth of insulation will be saved rather quickly in electricity costs.

Believe it or not, Montana gets up around 100 degrees for about 30 days or so in the summer. I've never seen the temperature in my loading room get over 85 degrees with no air conditioning, and even at -20 it seldom falls below freezing in there with no heat. When I'm going to be in there for the day, I turn on a 3000 watt electiric heater and I can run it up to 70 degrees within a couple of hours.

[timkelley]

Easiest way to size it is to go to Lowe's or HD and look at the end of the AC box. There is a chart giving square foot for each BTU size, pick the size of your room then go up One AC size. The manufacturers try to get a little too much from each unit so if you stick to the chart you will get one that will run a little too much. Also get a 220V unit if available and pay extra if you must for an Energy-Star approved unit. The chart is sized for an eight foot ceiling, if your ceiling will be higher plan accordingly.

Finally found somthin I know a little bit about on this site.:-D

[Char-Gar]

heating just in not an issue. The climate is tropical with parrots, bananas and such as that. We don't need heat in the house more than ten days a year. Even so a very cold day might be 50 degrees. A simple electric space heater to knock the chill is plenty.

Cost is an issue, so I can go with a contractor installed unit, just a plain jane window unit. I will have it placed before I bring in the gun safes and build work benches.

I take seriously the notion that a unit that is too large will not take out the water. I have heard that before.

I grew up down here and had guns and loading equipment all along. In any kind of air conditoned enviroment rust is not a big issue. I am far enough away from the Gulf of Mexico (25 miles) not to have much salt in the air.

I think the suggestion about going one size up from what is recommended for the area sounds like a good idea. Are teir any brands that are better than others or ones to be avoided?

[Buckshot]

Are teir any brands that are better than others or ones to be avoided?

.............You can check the various consumer reporting places on the web, home improvement websites and the like. They have reports and comparisons, etc.

Very possibly already required in your area, but if not explore the use and application of radiant barriers, 2x6 wall studs for insulation thickness, and finally 1 to 1.5" of styrofoam panel application under the final exterior finish. Neither the radiant barrier film nor the styrofoam panels are very expensive.

Consider the thickness of your common throwaway styrofoam ice chest and it's performance, and the value of it's insulation capabilities become evident.

.................Buckshot

[twotrees]

Ron/ Rareagle smiths double rifles and has sources none of the rest of us do. If you see a post from him, he will give you gospel.

Good Shooting,

TwoTrees

[Shotgun Luckey]

I would also consider a dehumidifier. I use one in the basement of the house when the AC is on, because eventhough it is cool in there, there is a lot of moisture coming up though the concrete. I don't know if one of those epoxy floor coatings whould help with the dampness coming through the concrete or not.

And don't forget to close of the space above the rafters, insulate the ceiling and make sure you have plenty of ventilation in the "attic"