Rob,
First, your compressor is NOT 5 hp; that is the "BS rating" they put on it when they determine how many watts it will take to burn up the motor (1 hp = 746 watts). In what I regard as consumer fraud, marketers (started by Sears BTW) list this useless information as "peak horsepower" to make people think they're buying more than they actually are. "FIVE HORSEPOWER" sounds like big-time power to those who don't understand the difference. Many manufacturers have now been forced to also list the real hp number as "run horsepower". Your 25 gal. Husky unit puts out 5.8 CFM at 90 PSI and runs on 115 volt, 15 amp circuit, so it might be 1.8 hp actually. If you'd like to know what you actually have, look at the amp-rating on the label of your machine's motor and apply the following formula: (Voltage) times (Amp-draw) times (Power-factor [.8 for 80% efficiency]) divided by 746. Example: 115v x 15amps x .8 ./. 746 = 1.85 hp.
BTW, most people would have trouble even lifting a real 5 hp electric motor.
Okay, "Rant Off."
At 5.8 cfm, your compressor will do just fine for inflations, blow-off air, nailers, a small die grinder, an impact wrench, and light (1/4 or 3/8") air-drive drills. You will have trouble with most sanders as they usually call for air volume (CFM-cubic feet per minute) well above what your unit will put out. If you're going to be spray finishing, you're about at the minimum point for CFM's required for a good HVLP conversion gun set-up, but you would do well to increase your storage capacity to smooth out "compressor pulse" in the airflow if you're spraying product while the compressor is actually running. There are two ways to do this. First, you can convert your piping system to storage by using larger diameter pipe (copper or steel only - see above thread). However, going from say 1/2" or 3/4" pipe to 1"or 1-1/4" pipe doesn't give you very much in the way of increased 'gallonage.' It will, however, increase your pipe and fitting cost substantially, and it's harder to solder properly for good joint seals. I find it much more cost efficient to install a supplementary tank in the system. They are easily available and a 20 gal tank rated at 125psi is not too pricey. Since you only need it for spray finishing, you can place the tank in your spray room (put the compressor outside the room for noise damping) and only pressurize the extra tank to 90psi (way more than enough for spraying) through a regulator when you are using the sprayer; the extra storage is not needed for either your shop or the garage. If, on the other hand, you want to make it integral for the whole system, you really should have a ASME rated tank that matches or exceeds your compressor's rating. That gets pricey, however, as a 20 gal tank that's ASME-rated at 140psi is likely to cost you about $250-300 which is almost what your compressor cost.
Based on your drawing, I'd suggest 2 distribution pipe sizes. From your compressor location on the shorter runs to the garage, the outside spud, and into the finish room, 1/2" type "L" copper should do fine (Don't forget your flexible jumper hose from the unit to the fixed piping). For the long run to the shop, you'll be happier with 3/4" type "L" copper, but you will have to be careful to pitch your piping so that the increased condensate you'll get in the larger diameter will drain properly. You won't enjoy the result if, when using your air, you wind up spraying oily water on whatever you're doing. The different area temperatures you mention will effect condensation in your lines, but the drains you install at the end of each run will handle that so long as you actually use them. Takes 2 seconds to open and close a ball valve to empty the collected water. Real easy.
Note on compressor oil. I strongly recommend that you use only 100% synthetic compressor oil, and change it once a year. You should be able to find it at Home Depot in the compressor section, and many compressor warrantees actually require it. The only down-side to it is that many filter/regulator units (you will need one in the spray room and the shop, optional but good in the garage), have polycarbonate collection bowls that will degrade from contact with any synthetic oil mist/condensate. You should therefore look for filter/regulator units with metal or glass bowls.
Hope this helps. If you have further questions, feel free to e-mail me or drop a PM through the board
Mark
PS: Since your compressor is on wheels, you need to do something to lock it in place. If you take the wheels off and mount it on a frame fixed to the floor, you won't have to worry about it being bumped or "walking" from vibration.
M
