We are in the process of converting what has been an unheated storage space above our garage into a finished area with 2 bedrooms and bath. It's about 500 sq ft of living space. We are planning on installing a central heating/AC unit in an adjacent portion of the attic that is unheated, and run air ducts and returns into the living area. The house is located in northern NJ, and we expect to be using these BRs primarily for family visits at Thanksgiving or Christmas time, but may also be used weekends in the summer. So my questions are:

A. Natural gas or electric? The main house uses gas, but to plumb a gas line up to the attic area may be difficult.

B. I know gas is less expensive to operate than electric heat pumps, but it is more expensive to buy and install the equipment. Given that the area will be heated for perhaps 10-15 days/year, with the rest of the time set to 50 degrees F, can the extra up-front expense of gas be justified?

C. If we go with gas, are there any issues around having a gas-fired furnace in an unfinished attic area? For example will I need to put up plywood to cover exposed roof joists?

Thanks.

Is this an attached garage or a detached garage?

Attached.

Trying to cover all the bases I can think of so everyone that might answer gets a better visualization of the place. The entry would be from outside and not from a current living space. (meaning heat from your current living space won't find its way there when its not in use.)

I live in a more temperate location and wouldn't consider electric where I am. Heat pump would be pricey and occupy space for the evaporator, electric baseboard heat cheap to install, ungodly expensive to run...and you'd have to maintain it when temps hover near freezing.

Personally, I preffer the natural gas route, Wall mounted infrared or blue flame heaters are cheap to buy and cheap to run. The major expense being running the gas to that area (not knowing your house its impossible to guess how hard or easy that would be). But those don't cover the air conditioning needs. If it was a single room a window unit could do that inexpensively.


How much of the work can you do yourself and how much do you have to farm out?

No - entry is up a stairway from our laundry area. Years ago we added a laundry room, office and 3-car garage to the house. We anticipated that some day we would finish off the area above the garage, so we built in stairs that go up from the laundry room and installed rough plumbing for the bath. Since then it's been unheated, unfinished storage space. So it's a pretty easy project - just some walls insulation, bath fixtures and tile, a bit of electric work, plus HVAC. Hope this helps clarify the project.

I've done some of this, but its not my main line of work, did my own, and did some on the side. Labor on any of them is going to play a large part.

They have ductless heat pump systems now that won't be intrusive in a space that small... provide heating and cooling both... but I have no idea what their costs are. But they eliminate some of the problems the others present. And might end up with the lowest labor charges. Something worth looking into if you haven't yet... The conventional ducted heat pump systems would be a huge job to install.

Here is a link to ONE manufacturers ductless units....
http://www.carrier.com/homecomfort/e...tless-systems/

At 500 ft. sq. you are looking at about a 1 ton unit for AC and a pretty small heater. With flex gas line, it is not much harder then pulling electric wire. Lots of time they go outside the house and run a small pipe chase. You might look at trying to extend the ductwork from the second floor if you have capacity. You could possibly bump up the fan speed to increase volume. You could supplement heating with small baseboard heat. If you go with the unit in an attic, there is no issue in unfinished spaces. They usually put them on a plywood deck and put a thin insulated rubber pad under the housing for the air handler. However, you may have to use X rated drywall to fire protection. A lot depends on your location and North NJ is probably a code specific area-I used to live in Cherry Hill.
Considering the time frame of usage, I would consider installing a subpanel for electric, use baseboard heat and window AC or set the small units in the walls. A low temp heat pump would also be possible but you are going to have to pull wire and probably use a sub panel too.