I would like to add AC and possibly heat to my garage so that I can work there. There seems to be two choices: (1) add a portable unit, or (2) extend the duct system from my house. I still need to be able to open and close the garage door so the garage is not energy efficient. Does anyone have any recommendations? I am assuming that my HVAC system can accommodate the additional 400 square feet (depending on the answers I receive I will investigate that further). If I add a portable unit, can I keep a car in the garage as well? I was concerned with electric arcing (is that the proper term?) and gasoline. My gas hot water heater is also in the garage so would that be a problem? If you recommend a portable system, any suggestions as to model/brand? Any help would be appreciated. Thanks in advance.

Unless there are some unusual obstacles, extending the existing duct work should be much cheap-er. We are talking occasional use, weekends and evenings? Would it work if you had to forgo using it in the very hottest or coldest weather? Surely your HVAC system has some reserve. Add 400 sq. ft to a 2000 sq. ft house, and you add 20% Even in weather where the system runs 40% of the time, the 20% increase would mean 48%. You would lose all the heat or cool when you opened the garage door, but if left closed while you were working, the system should recover.

As for adding a system, I hardly see how it would be much more of a hazard than the electrical equipment you may also be using. One note. Gasoline fumes are heavy. When I worked in a paint lab, all the electrical equipment was kept 42'' off the floor. A ceiling or attic mounted unit should be less of a problem.

There are gas hot water heaters specifically designed to be safe in garages. Others are now mounted up on platforms further from the floor.

In our area you are not allowed to install supply vents from the main house into a garage for safety reasons. IF the car is running and the system is not the fumes from the car can drift back into the supply runs toward the air handler and into the house. Another reason not to is---your system is designed to have a certain amount of air going back through the return filters and recirculate through the supply vents. When you install vents in the garage you now are shorting the amount of return air needed for the system to operate properly. This can and will cause a negative pressure on the house and if you have a crawl space you will get air pulled in from the crawl and the attic space through any holes, cracks, crevices etc in order to make up the air shortage caused by the supply vents in the garage. The best thing would be to install a ductless mini-split for the garage----run it when you need it--should run about 1800---2400 depending on size.
Keep the house separated from the garage---you don't want to wake up DEAD!!

Thanks! I had talked to an HVAC person here who told me the same. I opted for a portable a/c unit, 2' off the floor (since I have an old car in the garage - it doesn't run but still has gas in it; no apparent fumes.) It's being hooked up this week.

KO