If your current ductwork can handle the airflow required of an air conditioner matched to your home's needs (you NEED a load calculation to determine size requirements), I would consider installing a split air conditioner (not heat pump) and indoor coil to go with your existing furnace. There are variables involved, and ductwork/airflow is especially of importance in this case, especially in older homes (how old is your home?). Higher efficiency furnaces/air conditioners/heat pumps need more airflow than older systems, resulting in problems in retrofit installations with undersized ductwork. As I've said before, ductwork is an often overlooked element of the installation but is extremely important in overall comfort/efficiency. Unfortunately not all contractors are well versed with duct sizing, and with existing ductwork systems in older homes, it's often impracticle to change the ductwork. But with a load calculation and envelope improvements, oftentimes a knowledgable contractor can provide a good solution. Another possible option would be ductless minisplit systems such as Mitsubishi's Mr. Slim system. They work very well and I believe in the product, but if you have existing ductwork I would try to go with central a/c.

Have you gotten any estimates yet?

What is the model/information of your current furnace? Full model number preferred -- should tell us your blower/heat capacity.

This post was edited by ryanhughes on Thu, Feb 14, 13 at 13:50

So to be clear, you have boiler not a forced air gas furnace?

You might think about mini splits. They don't require a ductwork system. Not exactly esthetically pleasing to the eye. If not mini splits or window units, then you would be faced with installing a ductwork system.

Post back to clarify method you heat.

IMO

Looks like tiger is right and I missed the part about not having air ducts. By high efficiency furnace the OP likely meant condensing boiler. If that's the case, I agree with the recommendation of mini-splits or a high-velocity ducted system, which would allow for smaller duct sizes (if feasible).

Where in MA are you, coastal or inland? You used "window unit" as in one. You have cooling in one room? Are you happy with the performance of the window unit(s)? Would you like to cool a larger proportion of your home?

Mini splits are a big performance and appearance (especially sound) improvement over window units. Some people think that the high wall mounted indoor units are not pretty, but there are alternatives, ceiling mounted "cassettes" among them. Though less efficient, they are plenty efficient, but a bit more costly. Look at the Sanyo, Mitsubishi and Toshiba web sites to learn a little and then post back with your questions.

Just about any heat pump system (central or mini) can be installed with only cooling or with heat too. You might want to run some numbers with your gas and electricity rates to see if a heat pump will work for you in the money department. Often the increased cost for adding heat is not significant and you are left with the differential between the fuel costs.

Our furnace is a high efficiency gas fired furnace with hot water baseboard heat. We are interested in a separate cooling system ....if ducts are small we are not adverse to installing them. . Can do that through closets from attic, etc.
Salbwil

Looks like OP does not know the difference between a boiler or hot air gas furnace.

Probably should consider mini splits and depending on gas and electric rates, might even take a look at HP mini splits for redundantcy and use in mild weather/shoulder mths. Just a thought.

IMO

Whether high velocity (smaller ducts), conventional, or mini splits are best will depend on your home's lay-out and your needs.

Will look into all these and thank you !