What is the best way to bring heating and cooling to an attached garage? Our HVAC is being replaced, and our large family needs the garage for living space. Wed be going from 1500 sq feet, to 1900 about... Its HOT here in summer, and COLD in winter. Portable, wall, and window AC and heating units don't cut it. The walls have drywall, but no insulation. I have a roll up door with no insulation, and a slopped roof with no insulation. We have contractors coming out to talk to us about replacing the HVAC and I want to ask what they can do to the garage. If my children have to use it for bedrooms as they get older, I want the AC/Heat to work just as well as the house. Any suggestions?
Converting a garage to a living space means applying all the features that you'd normally expect in a living space:
- Remove the rollup door and frame in the opening (or frame a new wall with an offset to create an externally-accessible storage space, as Ed Beal suggests). Install an insulated service door or window if desired.
- Insulate the walls and ceiling and apply vapor barrier.
- Run supply and return ductwork from the new HVAC system.
- Consider framing a floating, insulated floor over the slab
I think that you knew this was the answer but were looking for shortcuts. You've eliminated the shortcuts in your question by saying that window units don't do the job. I'm not surprised, and I'd be wary of the energy bills even if that was a workable solution.
Two long for a comment: Depending on the type of system you choose there can be many options. In the last few years I have been working more with split heat pump systems. These are easy compared to running new ducts and each zone can be adjusted. If a room is not in use the thermostat in that area can be set to a more energy efficient temperature. 2 copper tubes run to each unit from the compressor and on most of the residential 120v for the blower and valve are needed. Also a drain tube for the condensation . If upgrading your system some states have tax credits for these systems and the utility company in my area is also providing cash to the customer with the appropriate paperwork from the utility. A small split system for 2 bedrooms in the garage may be the least expensive route. It all comes down to the type of system you currently have and the location and size of the existing ductwork. Your HVAC contractor should give you at least several options.
There are two common methods:
Run HVAC main branch under floor. Most of the time the garage sits below the house flooring level (at least in areas I do work). So we would try to level the garage floor to the house level as best as we can. The extra work doing this pays off two-fold because not only does the garage seem to be more integrated with the house but you can also run electric there and sometimes plumbing.
The easier method is get a main branch up to your attic and then disperse from there. This is easier but I don't like suggesting putting duct work in an attic in a climate with severe temp swings. You will pay a lot of extra money in the long run and be asking why the air in this section of the house isn't cooling or heating as well as it could.
There is a third option and that is going right under the concrete slab in the garage but this should never been done for a variety of reasons. Mike Holmes would run the ducts under a subfloor. If that wasn't an option he would run it in bulkhead on the first floor. If you had a layout of your house, duct runs, and where everything is in comparison to basement walls (if there are any)/HVAC/framing I could give you a more exact answer.