3 A/C  units,  as long as the

3 A/C  units,  as long as the room is well insulated it does not add much.

I have 3 A/C units in the house in Arizona.   The train room (Window A/C) is well insulated and only has 2 exposed walls and a celling.   But at the same time it shares two inside walls with to other conditions spaces. 

I was surprised that the power bill actually was less when the 2nd A/C unit was installed on the home addition.   The new area of the house was better insulated than the older area of the house,  main A/C unit did not need to work as hard and the new unit just buffered the old exterior walls that are now interior walls, it actually cooled better. 

Your Exterior walls and ceilings need to be well insulated,  We alos have 3 pane insulated windows on the house too.

A/C

Im not sure how well the outside wall is insulated. It is  new home construction so I hope it wont be to bad. Although we do have a guy coming to give us an estimate on solar panels. I also put an insulation kit on the garage door.

Split Units

Split units usually work on 220 voltage. They draw less current than a 120 volt window unit.

Bernd

Garage Walls on the exterior

Garage Walls on the exterior are normally not insulated,   Only walls that are next to a living space are normally insulated.   

So you might end up boring a hole between studs and then filling the space with expandable foam.   People do that out here when insulating their garages.

Split a/c works for me

Just had a 1 ton split unit installed first of may,  and can do a full "Happy" dance.

For me.  Worth the cost.

Boudreaux,  Bayou Crest Express R.R.

So much rain these days,  Think my camel is Vapor locked!

As a home inspector and

As a home inspector and former custom home builder please leave access to your attic hatch and water heater for future repairs. Luckily it looks like the attic hatch is close to the entry door.

One thing to watch out for

One thing to watch out for with mini-splits is maintenance costs. The installation company won't tell you about this because they also usually do maintenance, and for that mini-splits are cash cows.

I had an old home that did not have ducting (hot water heat), so when we went to install A/C, we went with mini-splits. We wound up with seven compressors (outside part) and 12 evaporators (inside part). They worked great for several years, but when we went to set up a maintenance contract for the units, I was flabbergasted at the price.

Maintenance contracts (at least in the eastern half of the country) are generally written based on the number of compressors. If we'd had a single standard A/C system, the cost would have been reasonable - around $150 a year at the time. With seven compressors, the cost was - wait for it - seven times that amount, or about $1,050 a year!! There was no break for the mini-splits, not even for them all being in the same location!

Also, parts for mini-splits seem to be available for only a few years. After that you have to replace the entire system (inside and out) with the latest model, even if just one side has failed. In one case, we had an evaporator fail and were told we'd need to replace the compressor and both evaporators on that system, since the unit was several years old and no longer made (and used units are simply not available. They're destroyed when removed). Newer systems are even worse, since they can have three or four evaporators on one compressor. Manufacturers discontinue old designs and apparently keep few parts for older units in stock.

So check out the potential maintenance and repair costs before you go down that road. It may be better in the long run to extend your main system. Even if you need to upgrade the components, you'll find savings in the higher SEER values available today.

I have a small hunter window

I have a small hunter window unit that cools my entire train room 546sqft.  It is 118' outside and the little window unit can drop the place down to 72' if not cooler.  I can pre cool the room for events etc. it is 12000btu and I installed 18 to 20 years ago.  No issues with it.

On something like a shed or garage with an outside wall.  I would prefer a window type unit,  if anything happens and or it dies,  I can go down to Home Depot and by another one and push it back into the hole in the wall.

The funny part is that little window unit has out lasted 2 main house Heat Pumps during the time I lived in this house

Higher costs for maintenance understandable.

Most if not all home a/c units use hermetically sealed compressors.  That means that refrigerant returning to the suction side of the compressor cools the compressor motor windings.  Evaporator & condenser coils typically don't break unless your they are in a transport unit bouncing down the road.  If you get a leak in your system anywhere the refrigerant leaves, the compressor motor is no longer cooling.  The lifespan of the compressor is now similar to the lifespan of your car engine if you drain the radiator and then try to drive the car without coolant!  The compressor is probably the most expensive part of the system. 

Trucks run multi temp units where a front evaporator is the freezer, a bulkhead insulates the front from the rear compartment, and second evaporator cools the rear refrigerator, both running off one compressor.  Some trailers run three compartments with the front freezer, the center dairy & deli, the rear unit produce.  

If you pay for a maintenance contract on your a/c expect to increase the cost by multiplying the cost if you had one compressor by the number of compressors in the system.  A much better system would be one that uses one large capacity compressor with multiple evaporators on common plumbing and solenoid valves to shut off any areas when they are not needed to be cooled.

Since I worked in transport and not home or commercial air, I don't know if such a system is even available.

Actually it is the

Actually it is the electronics that make the new units run in the variable speed economy modes that cost.  The last unit cooled fine the issue was the electronics that ran it and the computer controls to make it run and start in the multiple economy modes.  It was not like the old Heat pump with just some contactors being on and off.  The controller failed and it is only replaced as an entire module,  you just can not by the replacement board etc. you need to buy the entire module and for our unit is was almost $2000 to get a new one ordered and replaced.   it was just a better option to replace the 10 year old unit with a newer one at that point

RedP.  Is that a single car

RedP.  Is that a single car garage?  Dimensions?

single car

Yes, it is a single car garage. I think it is a good size for the layout I plan to build.

Thank you everyone for the comments. Window A/C is out of the question because there isnt a window. As far the attic hatch goes, thats where the furnace is. I know its weird, but the builder tells me thats how they are building homes now. I guess the unit is pretty small.

Down here in Florida we are more concerned with the A/C than the furnace.

-Scott

Don’t need no stinking window!

Scott,

Just frame a rough opening for the housing/sleeve. The unit should come with dimensions, if not you can measure it your self. 
     There are DIY mini splits,,the line set is pre-charged with the refrigerant. You tube it. In my central Texas garage  I thought about using a PTAC, those are the units they use in hotels/motels. It does get toasty in the garage. I sweat for my job,,I do not want to sweat for my hobby. 
 

Greg

No window?

You don't need no stinckin window. Just call chainsaw man:

Dimensions?

Dimensions?

@Jim

I think its 12x24

Thanks.  I would guess the

Thanks.  I would guess the best layout that could be fit in a 12x24 would be an around the walls layout with a peninsula.  The Peninsula could be as wide as 5.5 feet and allow minimum radius of nearly 32"R.  That would create two pinch points of 24 inches each with benchwork of 12 inches narrow on one side and 18 inches on the other side.  You could play with those numbers a bit but probably at the expense of minimum radius.  A lift out would be needed at the doorway if you went with an around the walls format.

I don't particularly like mini-splits...

...since I own one and it is not what we should have been sold as a whole house solution.

However, this is pretty much the situation they are ideal for.

Unless you need it for vehicular access, I recommend insulating the garage door.

Mini-Split HVAC

If you are talking about a mini-split HVAC, I have had one (Mitsubishi) in my train outbuilding since 2012. Mine uses a 110V-20 amp circuit and it does not use much power at all. During the summer here in central Texas, it keeps my 15 x 25 train room portion of the outbuilding very comfortable and does the same during our usually mild winters. It worked great even during our "Snowmageddon" during February 2021 (when we had power). 

The only thing that you would need to look out for is that the company installing the system is fully trained and knows how these systems are supposed to be installed and maintained.

Awesome I have one too!

My new room is a casita with wall mounted AC. In the Desert. The unit is wall mounted on the left hand side with remote control. When I am there in August will take picture of that. 

AC Units

I have seen ads for the last year or so on some mini AC units good for a room. Developed for the military for desert use. They are suppose to be pretty efficient. 

Try these searches. Blast AC, and Rapid Advanced Cooling Systems.

I have no idea how efficient they are or how long they last. My thought for home use would be to get one and turn the HIVAC system off and try one in what would be the warmest room in the house. If it works and they seem to have a good lifespan then to put one in each room and 2 in the kitchen/living room. And 2 more in the basement, maybe 3.

Advertise cost is suppose to be 140-600 dollars. Way cheaper the a new HIVAC system. We have 2 electric heaters in the basement that get use on coldest days to help out the HIVAC. Not sure how well they would do in a kitchen -living room combo though.

A possibility maybe,   Jack

Try these searches. Blast AC,

It is a swamp cooler aka a scam,  do not buy it.   You can not plop a A/C unit into a room with out an exterior component to remove the heat.   The heat energy removed needs to go someplace and putting it back into the same space does not work.  Those are a scam and run of the mill evaporative coolers aka swamp coolers.

For a proper A/C or refrigeration system to work you need a sealed Box aka a refrigerator / House / Car etc.   You remove the heat from the sealed space and push it outside the sealed box,   opposite if you are trying to heat a space aka heat pump.

An A/C - Heat Pump etc. will not work  if the condenser and the evaporator are in the same air space.  

mini splits

I did get a garage door insulation kit from Lowes. So im thinking with the Split A/C the room will be comfortable.

-Scott

Update

I actually accomplished something. The split A/C unit has been installed and it is working beautifully. In this Florida heat, im impressed. Now on to the next  step in this journey. let the games begin.